naujametė fizikos konferencija pranešimų tezėsltf2015.ftmc.lt/ltf2015 abstracts.pdf ·...

Naujametė fizikos konferencija

Pranešimų tezės

LT

2015 m. sausio 2-3 d. Vilniaus Universitetas, Fizikos fakultetas

Organizatoriai

Institucijos

Žmonės

Audrius Alkauskas | Fizinių ir technologijos mokslų centras Kęstutis Aidas | Vilniaus universitetas Ramūnas Augulis | Fizinių ir technologijos mokslų centras Deividas Sabonis | Miuncheno technikos universitetas Julius Janušonis | Groningeno universitetas Vytautas Butkus | Vilniaus universitetas Jonas Berzinš | Vilniaus universitetas

Rėmėjai

© Fizinių ir technologijos mokslų centras

FIZINIŲ IR TECHNOLOGIJOS MOKSLŲ

LIGHT

CONVERSION

3

Konferencijos programa

SAUSIO 2 D., PENKTADIENIS 9:00 Vidmantas Gulbinas, TBA (FTMC) 9:50 Julija Sabataitytė,Podoktorantūros stažuotės Lietuvoje ir kiti ES struktūrinės paramos instrumentai

nuo 2015 m. (LMT) 10:20 Karolis Misiūnas, Brownian Dimers in Narrow Channels (Cambridge University)

— kavos pertrauka — 11:20 Žilvinas Rinkevičius, A hybrid QM/CMM approach for (non)linear optical properties of molecules in

heterogeneous environments (KTH Royal Institute of Technology) 11:50 Bronė Lenkevičiūtė, Investigation of Electroluminescence Features of Vacuum Deposited Organic

Materials TPD, Ir(Fppy)3, AlQ3 and Spin-coated CdSxSe1-x/ZnS Quantum Dots Layers (VU) 12:20 Julius Janušonis, Frequency tunable surface magnetoelastic waves (University of Groningen)

— pietų pertrauka — 14:00 Gintaras Valušis, Saulėtekio Slėnis (FTMC) 14:30 Aleksejus Kononovičius, Complexity and statistical physics of herding behavior (VU)

— kavos pertrauka — 15:30 Saulius Valatka, Towards the solution of N = 4 super Yang-Mills (King’s College London) 16:00 Dominyka Dapkutė, Accumulation, distribution and elimination of quantum dots in different types of

human breast cancer cells (Nacionalinis Vėžio Institutas) 16:30-18:30 STENDINIŲ PRANEŠIMŲ SESIJA 19:30 KONFERENCIJOS VAKARIENĖ

SAUSIO 3 D., ŠEŠTADIENIS 9:00 Ramūnas Valiokas, Medžiagų ir gyvybės sandūros (FTMC) 9:45 Giedrius Laukaitis, Bronė Narkevičienė, Fizika KTU (KTU) 10:20 Gediminas Kiršanskas, Spin induced sub-gap states in superconductor/quantum dot/

superconductor junctions (Niels Bohr Institute) — kavos pertrauka —

11.20 Mindaugas Karčiauskas, Cosmological Inflation and the Origin of Structure in the Universe (Helsinki Institute of Physics)

11:50 Andrius Melninkaitis, Time-Resolved Digital Holographic Imaging of Laser-Induced Damage in Thin Films (VU)

12:20 Laura Paulina Šinkūnaitė, Jet substructure for LHC Run 2 (University of Glasgow) — pietų pertrauka —

14:00 Mikas Vengris, Ultrafast processes explored by multi-pulse transient absorption spectroscopy (VU) 14:45 Aloyzas Šiušys, Magnetic core-shell (Ga,Mn)As nanowires (Polish Academy of Sciences)

— kavos pertrauka — 15:45 Maksym Ivanov, Broadband optical vortex (Taurida National V.I.Vernadsky University) 16:15 Evaldas Balčiūnas, Novel materials for tissue engineering via direct laser writing (Institute for

Electronic Structure and Laser, Heraklion) 16:45 Vytautas Balevičius, Relaxation dynamics within carotenoids via high frequency stretching modes

(VU)

4

Kviestiniai pranešėjai

Vidmantas Gulbinas Fizinių ir technologijos mokslų

centras

Julija Sabataitytė Lietuvos mokslo taryba

Gintaras Valušis Fizinių ir technologijos

mokslų centras

Giedrius Laukaitis Bronė Narkevičienė

Kauno technologijos universitetas

Ramūnas Valiokas Mikas Vengris

Fizinių ir technologijos mokslų centras

Vilniaus universitetas

5

Stendiniai pranešimai

1. Kęstutis Aidas, Photoabsorption of acridine yellow and proflavin bound to human serum albumin studied by means of quantum mechanics/molecular dynamics

2. Audrius Alkauskas, First-principles theory of nonradiative carrier capture via multiphonon emission 3. Giedre Marija Archipovaitė, Generation and parametric amplification of broadband pulses at 2 μm 4. Jogundas Armaitis, Collective modes of binary Bose mixtures 5. Vytautas Astromskas, Comparison of Spectroscopic and Imaging Performance of Schottky CdTe Medipix3RX and HEXITEC

Pixelated Detectors 6. Tomas Babelis, Study of the initial state in the relativistic heavy-ion collisions 7. Laura Baliulytė, Quantum mechanical study of the proline molecule fragmentation by low energy electrons 8. Tadas Bartulevičius, Investigation of Ultrashort Pulse All-in-fiber Oscillator Using Different Dispersion Chirped Fiber Bragg

Gratings 9. Gintarė Batavičiūtė, Damage probability analysis as a tool to identify defects within individual layers of thin film coated optics 10. Violeta Bėčytė, Study of magnetic and structural properties of cobalt-manganese ferrite nanoparticles obtained by

mechanochemical synthesis 11. Vytautas Butkus, Vibronic coherence in photosynthetic molecular complexes 12. Eglė Daugėlaitė, Magnetic resonance imaging of superparamagnetic iron oxide nanoparticles distribution in vivo 13. Jevgenij Garankin, Thermal neutron detection using thin PEN film with layer of FeB micropatricles 14. Andrius Garbaras, Yeast cell encapsulation with the polypyrrole 15. Nail Garejev, Generation of Third, Fifth and Seventh Harmonics in Bulk Solids with Intense Mid-Infrared Pulses 16. Ieva Gražulevičiūtė, Self-reconstructing, carrier envelope phase-stable spatiotemporal light bullets 17. Simonas Grubinskas, AdS/CMT correspondence and field theory interpretations 18. Greta Jarockytė, Cellular uptake and cytotoxicity of photoluminescent Au-BSA nanoclusters in breast cancer cells 19. Karolis Jurkus, Output beam power dependence on crystal temperature in a doubly resonant optical parametric oscillator 20. Agnė Kalnaitytė, Photostability and toxicity of CdSe hydrophilic quantum dots in media with freshwater algae 21. Rytis Kazakevičius, Lévy flights in non-homogeneous media and 1/f noise 22. Gabija Kiršanskė, Photoluminescence study of excitonic Mott transition in coupled InGaAs quantum wells 23. Vilius Kripas, Search for tt resonances with the CMS-detector 24. Kasparas Krivas, Influence of interface roughness in quantum cascade lasers 25. Svetlana Malickaja, Study of Artificial Light Harvesting Antennae by Quantum Chemical Methods 26. Tomas Marčiulionis, Simulation of exciton evolution in a single light-harvesting complex LH2 27. Aidas Matijošius, Multicolour optical vortices formation by radial polarization S-wave plate converter 28. Paulius Mikulskis, Performance of alchemical free energy methods in ligand-binding simulations 29. Martynas Miškinis, White light continuum seeded picosecond OPA 30. Karolis Parfeniukas, Nanofocusing x-ray optics for synchrotrons 31. Domantas Peckus, Ultrafast relaxation dynamics of excited plasmons in diamond like carbon:Cu and Ag nanocomposite films 32. Evelina Pozingytė, Temperature-dependent Photoreflectance and Photoluminescence Spectroscopy of InAs Quantum Dots-in-

a-Well Structures 33. Kipras Radeckas, Femtosecond stimulated Raman scattering: theory, apparatus and applications 34. Tomas Rindzevičius, Wafer-scale leaning Ag and Au nanopillar structures for surface-enhanced Raman scattering

applications 35. Augustinas Ruibys, Simulation of electrical properties in femtosecond-laser sulfur hyperdoped silicon solar cells 36. Deividas Sabonis, Investigation of Ultrashort Pulse All-in-fiber Oscillator Using Different Dispersion Chirped Fiber Bragg

Gratings 37. Linas Šimatonis, Combined Micro-fabrication Employing Lloyd’s Mirror Interferometer and Direct Laser Writing systems 38. Milda Skeivytė, Supercontinuum generation in solid-state dielectric media with picosecond laser pulses 39. Akvilė Šlėkaitė, Gold nanoclusters for X-ray and fluorescence bioimaging 40. Marius Stalnionis, Magnetic resonance imaging of superparamagnetic iron oxide nanoparticles distribution in vivo 41. Paulius Stanislovaitis, Improvement of temporal coherence of down-converted waves in optical parametric amplifier with

incoherent pump 42. Paulius Stanislovaitis, Formation of optical vortices with topological charge |l| = 2 using the radial polarization converter 43. Simona Streckaitė, Influence of Silver Nanoparticles on Optical Properties of Organic Dyes 44. Linas Šimatonis, Combined Micro-fabrication Employing Lloyd’s Mirror Interferometer and Direct Laser Writing systems 45. Giedrius Tušinskis, Energy transfer of an EM field scattered by a finite composite set of cylinders 46. Monika Venčiauskaitė, A study of the fluctuating initial states for relativistic hydrodynamics applied for the heavy ion

collisions at LHC energies 47. Vladislava Voiciuk, Redefining the established understanding of excitation dynamics of photochromic oxazines

ŽODINIAI PRANEŠIMAI

7

Naujametė fizikos konferencija LTΦ 2015

sausio 2-3 d. | Vilniaus universitetasLTŽodinis pranešimas

Brownian Dimers in Narrow Channels

Karolis Misiunas, Stefano Pagliara, Ulrich F. Keyser

Cavendish Laboratory, University of Cambridge, UK

Diffusion inside channels relates to a wide range of phenomena in nature. For instance, biological cells have protein channels that mediate transport of molecules into and from the cell. The industrial applications include filtration and diffusion through porous materials. For this reason we studied Brownian particle interactions inside the channels. Previously the hydrodynamics was often assumed to have a negligible effect on the interaction. We show the opposite

8



A hybrid QM/CMM approach for (non-)linear optical properties of molecules in heterogeneous environments

Žilvinas Rinkevičius1

1 Division of Theoretical Chemistry & Biology, School of Biotechnology, KTH Royal Institute of Technology, Roslagstullsbacken 15, Albanova University Center, Stockholm,

Sweden

We have developed a novel hybrid density functional theory/molecular mechanics (QM/CMM) approach for modeling of linear and non-linear properties of molecules in heterogeneous environments consisting from organic/inorganic and metallic parts. The organics/inorganic part of heterogeneous environment is described by conventional non-polarizable force field, and metallic part of heterogeneous environment is described by capacitance-polarization model, which allows for free redistribution of charges in the metallic part of the environment influenced by remaining parts of the system (QM region and non-metallic MM region). We have successfully applied our developed QM/CMM approach to study UV/Vis absorption [1], electronic circular dichroism [2], second harmonic generation [3] and two-photon absorption of molecules absorbed on various gold surfaces. Apart presenting obtained results we also discuss future development of QM/CMM approach and its potential applications in modeling plasmonic interaction between metal nanoparticles and molecules.

Literature [1] Z. Rinkevicius, X. Li, J. A. R. Sandberg, K. V. Mikkelsen, and H. Ågren, J. Chem. Theory Comput. 10, 989 (2014). [2] X. Li, Z. Rinkevicius, and H. Ågren, J. Phys. Chem. C 118, 5833 (2014). [3] Z. Rinkevicius, X. Li, J. A. R. Sandberg, and H. Ågren, Phys. Chem. Chem. Phys. 16, 8981 (2014).

9



Investigation of Electroluminescence Features of Vacuum Deposited Organic Materials TPD, Ir(Fppy)3, AlQ3 and Spin-

coated CdSxSe1-x/ZnS Quantum Dots Layers Brone Lenkeviciute1, Mantas Vitkus1, Giedrius Juska1, Kestutis Arlauskas1

1 Department of Solid State Electronics, Vilnius University, Sauletekio av. 9, III building, 2040 Vilnius, Lithuania

The multiple organic material layers were vacuum deposited and quantum dots (RQD) were spin-coated onto by ITO covered glass substrate and their electrical and electroluminescence (EL) features were investigated.

There were made 3 samples with structure ITO/TPD/Ir(Fppy)3/RQD/AlQ3/LiF/Al/Ag The concentration of spin coated quantum dots in solution was changed from 20mg/mL to 5mg/mL.

The family of Volt-Ampere Characteristic (j-V) of hybrid material layers was measured. It is demonstrated that smaller RQD concentration creates bigger injection of electrons from AlQ3 into Ir(Fppy)3 and RQD emission layers.

The EL of ITO/TPD/Ir(Fppy)3/RQD (20mg/mL)/AlQ3/LiF/Al/Ag was observed at 17 V threshold voltage while the EL of ITO/TPD/Ir(Fppy)3/RQD (10mg/mL)/AlQ3/LiF/Al/Ag

was observed at 6,2V threshold voltage. And the best EL result was given of ITO/TPD/Ir(Fppy)3/RQD (5mg/mL)/AlQ3/LiF/Al/Ag. Investigation showed that EL in 450 nm to 750 nm wavelength range with comparatively small threshold voltage can be obtained from the structure formed of only two sequent emissive layers of organic material Ir(Fppy)3 and CdSxSe1-x/ZnS quantum dots.

10



Frequency tunable surface magnetoelastic waves

Julius Janušonis, Chia-Lin Chang, Ra‘anan I. Tobey

Zernike Institute for Advanced Materials, University of Groningen, Groningen, Netherlands

An important goal of materials science is the discovery and manipulation of material properties which affect their functionality. In recent years ultrafast strain engineering came into consideration enabling access to a wide range of phenomena - altering onset of the multiferroic properties in transition metal oxides and modification of the electrical and optical properties of semiconductors to name a few. On the intersection with the field of ultrafast magnetism ultrashort acoustic pulses were used for driving the magnetic response in ferromagnets [1], dilute magnetic semiconductors [2], a method has been proposed to achieve magnetization reversal in high magnetostrictive materials [3] thus potentially leading to non-volatile memory applications.

Here we demonstrate a feasible way to generate propagating spin resonances using pulsed laser excitation. It has been shown that in a transient grating geometry a narrowband, widely tunable strain wave is launched in a thin film ferromagnet, subsequently coupling to a magnetic degree of freedom and resonantly driving propagating spin waves.

Planar propagation facilitates control of the spin wave and long propagation distance (>20μm) enables it to act on remote spin ensembles. Spin imbalances created via remote spin pumping, focusing, guiding with phononic structures and location specific modifications of magnetic properties using elastic wave are envisaged as possible applications.

Literature [1] J. W. Kim, M. Vomir, J.Y. Bigot. PRL 109, 166601 (2012). [2] A.V. Scherbakov et. al. PRL 105, 117204 (2010). [3] O. Kovalenko, T. Pezeril, V. V. Temnov. PRL 110, 266602 (2013).

11



Complexity and statistical physics of herding behavior

Aleksejus Kononovičius1, Vygintas Gontis1 and Julius Ruseckas1

1 Institute of Theoretical Physics and Astronomy, Vilnius University, Lithuania

Foundations of statistical physics were laid down 150 years ago by the works of Maxwell, Boltzmann and numerous other physicists, who strived to provide theoretical explanation for the laws of thermodynamics, which at that time we known only from the experiments. The main idea behind Maxwell’s and Boltzmann’s, assumption of molecular chaos, approach was borrowed from the works of their contemporaries, such as Quetelet, Comte and Mill, who studied demographical data [1]. At that time social sciences provided new ideas and tools for physics. Since then physicists were able to make significant progress – these tools were not only used to solve classical problems, but they were also improved to tackle other, more complex, problems.

Since the 1950s physicists started to think about the dynamics of open systems and the observed self-organization phenomena [2]. The importance of non-linearity and complexity was embraced. In the last 20 years building upon this foundation new interdisciplinary field of econophysics started to emerge [3]. The main aim of this new field was to understand the complexity behind socio-economic systems by using the experience, ideas, tools and frameworks nurtured by physics.

We contribute to the developments in econophysics by studying herding behaviour and its applications to the modelling of complex socio-economic systems. By using enhanced implementations of simple mathematical herding model proposed by Kirman, we were able to reproduce various stylized facts observed in real socio-economic systems. Namely we were able to reproduce such general features of many complex systems as 1/f spectra, power-law distribution and multifractality [4]. We have also directly related the size of the modelled system to its non-extensivity [5]. Furthermore we were able to precisely reproduce empirical distribution and spectral density of high-frequency absolute returns in the financial markets [6].

Literature [1] P. Ball, Physica A 314, 1-14 (2002). [2] H. Haken, Synergetics, an Introduction (Springer-Verlag, New York, 1983). [3] B. M. Roehner, Science and culture 76, 305-314 (2010). [4] A. Kononovicius, V. Gontis, Physica A 391, 1309-1314 (2012). [5] A. Kononovicius, J. Ruseckas, EPJ B 87, 169 (2014). [6] V. Gontis, A. Kononovicius, PLoS ONE 9, e102201 (2014).

12



Towards the solution of N = 4 super Yang-Mills

Saulius Valatka

King’s College London, Department of Mathematics, The Strand, London WC2R 2LS, United Kingdom

While the Standard Model of particle physics is being continuously tested experimentally to unprecedented accuracy in the LHC, attempts at calculating quantities such as the mass of the proton analytically are still far beyond our reach. Naturally, when faced with a problem that seems intractable, we go back and start with something similar yet simpler. The N = 4 super Yang-Mills theory is often called the harmonic oscillator of quantum field theories, yet it is similar enough to Quantum Chromodynamics that we can actually learn something useful by studying it.

In this talk I will be addressing the N = 4 super Yang-Mills theory and the most recent advances towards solving it. I will briefly walk through some of the amazing features this theory exhibits, the most famous undoubtedly being the AdS/CFT duality – the statement that this 4 dimensional QFT is dual to an 11 dimensional string theory. Furthermore, this dual system turns out to be integrable, I will briefly explain how this implies that it can roughly be decomposed into an infinite set of harmonic oscillators. Ultimately I will review some of the most recent work in this area [1, 2], which makes a big step towards solving the spectral problem in N = 4 super Yang-Mills exactly.

Literature [1] N. Gromov, F. Levkovich-Maslyuk, G. Sizov and S. Valatka, JHEP 1407, 156 (2014) [2] N. Gromov, V. Kazakov, S. Leurent and D. Volin, arXiv:1405.4857 [hep-th] (2014)

13



Accumulation, distribution and elimination of quantum dots in different types of human breast cancer cells

Dominyka Dapkutė1,2, Simona Steponkienė1

1Biomedical Physics Laboratory, National Cancer Institute, Lithuania; 2Faculty of Natural Sciences, Vilnius University, Lithuania;

A few decades ago it was noticed that cancerous tissue is hierarchically organized and contains a small subpopulation of cancer stem cells (CSCs) that are associated with tumour initiation, regeneration, metastasis, multi-drug resistance [1]. Therefore it is very important to target and eliminate these aggressive tumorigenic cells. Quantum dots (QDs) are semiconductor fluorescent nanoparticles. They can serve as a platform for biologically active compounds such as antibodies and/or drugs and due to their unique optical properties QDs can be used as diagnostic agents [2]. However, knowledge about their both non-specific and specific accumulation, distribution and elimination in different types of cancer cells is still limited. In our study we used two human breast cancer cell lines – MCF-7 and MDA-MB-231. To determine the stem-like properties of cells, we used colony formation, resistance to chemotherapeutic drugs and immunophenotyping assays. Flow cytometric analysis and spectroscopy showed the quantitative accumulation and elimination kinetics of the carboxyl-coated Invitrogen 625NC QDs in cancer stem-like cells and cancer non-stem cells. Distribution of QDs study by Nikon C1si laser scanning confocal microscope revealed their colocalization with different cellular compartments – after endocytosis they are localized in early endosomes and after 24 hours they are found in both late endosomes and lysosomes. ACKNOWLEDGEMENTS. This study was supported by the project „Mesenchymal stem cell and cancer stem-like cell response to nanoparticle treatment“(TAP LLT 13-016) funded by Joint Lithuanian–Latvian–Taiwanese Research Program.

Literature [1] T. Reya, S. Morrison, M. Clarke et al., Nature 414, 105-111 (2001). [2] M. A. Walling, J. A. Novak, J. R. E. Shepard, Int. J. Mol. Sci. 10, 441-491 (2009).

14



Spin induced sub-gap states in superconductor/quantum dot/superconductor junctions

Gediminas Kiršanskas1,2, Moshe Goldstein3, Karsten Flensberg1, Leonid I. Glazman4, and Jens Paaske1

1 Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark

2 Mathematical Physics and Nanometer Structure Consortium (nmC@LU), Lund University, Box 118, 221 00 Lund, Sweden

3 Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel

4 Department of Physics, Yale University, New Haven, CT 06520, USA

We examine the emergence of sub-gap states in a junction consisting of two superconducting leads coupled to spinful Coulomb blockaded quantum dot. Such bound states have recently been observed in several experiments [1-3]. The system is modeled by an effective Kondo model, which gives rise to so-called Yu-Shiba-Rusinov states inside the gap [4]. The bound states and their energy is found using the Yosida's wavefunction ansatz approach [5,6]. We determine the dispersion of these states with an applied phase difference across the junction and study their dependence on an applied magnetic field. Also the effects of coupling asymmetry to the leads and deviation from the particle-hole symmetric point are addressed.

Literature [1] R.S. Deacon et al., Phys. Rev. Lett. 104, 076805 (2010).

[2] W. Chang et al., Phys. Rev. Lett. 110, 217005 (2013).

[3] E. Lee et al., Nat. Nanotechnol. 9, 79 (2014).

[4] L. Yu, Acta Phys. Sin. 21, 75 (1965); H. Shiba, Prog. Theor. Phys. 40, 435 (1968); A.I. Rusinov, Zh. Eksp. Teor. Fiz. 56, 2047 (1969).

[5] K. Yosida, Phys. Rev. 147, 223 (1966).

[6] T. Soda et al., Prog. Theor. Phys. 38, 551 (1967).

15



Cosmological Inflation and the Origin of Structure in the Universe

Mindaugas Karciauskas Physics Department and Helsinki Institute of Physics, PO Box 64, FIN-00014 University

of Helsinki

The standard Hot Big Bang cosmological model proved to be very successful in explaining the evolution of the Universe right from when it was only 1 second old up to relatively recent times. Despite its successes, however, it cannot account for the current evolution of the Universe as well as for its very peculiar initial conditions. The Hot Big Bang model is also mute about the origin of the seed density perturbation which kickstarted the growth of structure, such as galaxies and clusters of galaxies. Many questions of initial conditions, on the other hand, are successfully addressed by the model of cosmological inflation. In my talk I will introduce some of the basic principles of inflation and discuss its current observational status. Recently, the results of the Planck satellite and BICEP2 observations received a lot of media attention. I will mention some of these results and what they can teach us about inflation.

16



Time-Resolved Digital Holographic Imaging of Laser-Induced Damage in Thin Films

Nerijus Šiaulys, Andrius Melninkaitis

Laser Research Center, Vilnius University, Saulėtekio al 10, 10223 Vilnius, Lithuania

Thin film technology allows integration of desired spectral properties into single optical component and thus is essential for laser applications. Furthermore vast majority of ultra-short (fs) lasers require coatings that operate at extremely high peak- or average- powers, close to so called laser-induced damage threshold (LIDT) limit. Due to low absorption and better LIDT performance dielectrics are preferred materials for coatings layers. Although dielectric layers are transparent at low or moderate optical intensity they become strongly absorbing once the certain intensity level is exceeded. At this point dielectric material develops a metal-like behaviour and possesses strong linear absorption of the laser energy: a runaway process can take place leading to the thermal and mechanical damage which is considered as a permanent change of optical characteristics. As the generated carriers have a limited lifetime, a sufficiently high optical energy must be provided within a short time thus making direct observation of damage process rather complicated. The understanding and characterization of these effects were two main objectives of this work. While seeking to investigate the fundamental aspects of interaction between femtosecond laser irradiation and optical coating we performed series of time-resolved digital holographic microscopy[1] observations of femtosecond laser damage initiation. The transient processes were directly observed in single layer dielectric Ta2O5 thin films of different thicknesses. The femtosecond (λ=1030nm, τ=300fs) pump fluence was varied within the range below and slightly above the damage threshold while capturing optical response of irradiated site in transmission mode with visible pulses of 25 fs duration. Kerr effect and laser-induced free-electron gas generation were captured during the pump pulse propagation as well as the early material modification dynamics after exposure. The fundamental time constants and values that drive the damage processes were extracted by changing the time delay between the pump and probe pulses. Based on these results the amplitude and phase information is traced back to the permittivity and hence electronic density[2] in the films.

Literature [1] T. Balčiūnas et al. Opt. Lett. 33(1), 58 (2008) [2] N. Šiaulys et al. Opt. Lett. 39(7), 2164 (2014)

17



Jet substructure for LHC Run 2 Laura Paulina Šinkūnaitė1,2

1 University of Glasgow, Glasgow, United Kingdom 2 DESY, Zeuthen, Germany

This work presents a number of methods performed on jet substructure for top-quark tagging. Three different functions are studied: angular correlation function (ACF) [1], angular structure function (ASF) [2], and energy correlation function (ECF) [3]. Physics of boosted objects is reviewed in general and a brief introduction to the theoretical motivations for jet substructure analysis is given. A novice idea of using ACF to extract angular and mass scales within a jet without referencing to a clustering algorithm, i.e. an alternative algorithm for top-quark tagging, is tested.

Literature [1] M. Jankowiak and A. J. Larkoski, Jet Substructure Without Trees, arXiv:1104.1646v4 [hep-ph] (30 Jun 2011) [2] M. Jankowiak and A. J. Larkoski, Angular Scaling in Jets, arXiv:1201.2688v2 [hep-ph] (6 Apr 2012) [3] A. J. Larkoski, G. P. Salam and J. Thaler, Energy Correlation Functions for Jet Substructure, arXiv:1305.0007v3 [hep-ph] (10 Jul 2013)

18



Magnetic core-shell (Ga,Mn)As nanowires Aloyzas Šiušys, J. Sadowski, S. Kret, T. Wojciechowski, K. Gas, T. Story, and

M. Sawicki

1 1Institute of Physics, Polish Academy of Sciences, Warszawa, Poland 2MAX-IV -Laboratory, Lund University, Lund, Sweden

After almost two decades of extensive research activity focused on (Ga,Mn)As dilute ferromagnetic semiconductor, there are still some areas of investigations of this material which are open for further research [1-3]. One of them is the fabrication and study of low dimensional structures (or nano-structures following the modern nomenclature) based on (Ga,Mn)As. Usually in the “nanoworld” the objects are fabricated following one of the two different approaches: a top-down – which is based on application of subtle nano-litographical procedures (typically a combination of e-beam litography and optical lithography), or a bottom-up approach involving elaborate procedures of epitaxial growth. The latter is extremely difficult to apply for (Ga,Mn)As, due to the specific conditions necessary to crystallize this ternary alloy with the Mn content high enough to provide the ferromagnetic phase transition (above 1 at.% of Mn). I will show how it is possible to get around this limitation; i.e. how the self-assembled one dimensional structures based on (Ga,Mn)As can be obtained by a bottom-up approach. I will focus mainly on the 1-D case, i.e. I will present the fabrication methods and selected properties of 1-dimensional-like nanostructures (nanowires) comprising (Ga,Mn)As. In particular I will show how it is possible to obtain (Ga,Mn)As in a wurtzite phase, impossible to obtain neither in 2D (very thin films) nor quasi-3-D (thick epitaxial layers) geometries; and how the properties of wurtzite (Ga,Mn)As differ from those of this compound occurring in its “native” zinc-blende phase [4].

Literature [1] T. Dietl, H. Ohno, Rev. Mod. Phys. 86, 187 (2014). [2] H. Ohno, et. al. Appl. Phys. Lett. 69, 363 (1996). [3] T. Dietl, Nature Mat. 9, 965 (2010). [4] A. Šiušys, J. Sadowski, M. Sawicki, S. Kret, T. Wojciechowski, K. Gas, W.

Szuszkiewicz, A. Kaminska, and T. Story, Nano Lett. 14, 4263 (2014).

19



Broadband optical vortex

M. Gecevicius1, M. Ivanov2 and V. Smilgevicius3

1University of Southampton, UK 2Taurida National University, Ukraine

3Vilnius University, Lithuania

We have theoretically and experimentally showed the simple and effective way of generation of optical vortices by use of S-wave plate (plate, fabricated by femtosecond laser writing in silica glass) and polarization filtering. This method allows generation of optical vortex at broad range of wavelength (more than 2 octaves). Light passing after S-wave plate, fabricated for certain wavelength, and polarization filter converts into two parts: optical vortex and noise. Form and weight of noise part depends on wavelength. We showed efficiency of vortex-noise conversion at the range of wave lengths 250-1200 nm.

20



Novel materials for tissue engineering via direct laser writing

Evaldas Balčiūnas1,2, Rashid Nazir3, Daniel T. Gryko3,4, Anthi Ranella1 and Maria Farsari1

1 Institute for Electronic Structure and Laser, Foundation for Research and Technology – Hellas, Heraklion, Greece.

2Institute of Biochemistry, Vilnius University, Vilnius, Lithuania. 3 Faculty of Chemistry, Warsaw University of Technology, Warsaw, Poland.

4 Institute of Organic Chemistry, Polish Academy of Sciences, Warsaw, Poland.

In this work we have studied the polymerization thresholds of three novel groups of photoinitiators, used for laser multiphoton polymerization – D-π-A-π-D ketone-based compounds, thioxanthen-9-one compounds and anthracene-based compounds. Some of these materials show comparable or even better structuring quality than commercially available photoinitiators, like 4,4’-bis(diethylamino)benzophenone [1].

Also, a new hybrid organic-inorganic Al-containing material has been synthesized. Sub- 200 nm resolution could be achieved using this material. Biocompatibility and chemical characterization of the material are presented.

Literature [1] R. Nazir, F. Bourquard, E. Balčiūnas, S. Pisarek, D. Gray, N. V. Tkachenko, M. Farsari and D. T. Gryko. Π-expanded α, β-unsaturated ketones – synthesis, optical properties and two-photon induced polymerization. Chem. Phys. Chem. 2014.

21



Relaxation dynamics within carotenoids via high frequency stretching modes

Vytautas Balevičius Jr.1, Leonas Valkunas1,2 and Darius Abramavicius1

1 Vilnius University, Sauletekio av. 9 bld.3., Vilnius, Lithuania 2 Center for Physical Sciences and Technology, Goštauto st. 11. Vilnius, Lithuania

Carotenoids are one of the most abundant species of natural pigment molecules. They serve a number of functions in the photosynthetic systems. First, they act as light harvesters in the blue-green spectral region. Secondly, they ensure the photoprotection, as they quench the triplet excited chlorophylls and singlet oxygen. Despite decades of continuous effort, their photophysics is still not fully understood, largely due to the fact that the absorption takes place not into the lowest-lying dark excited state S1, but to the short-lived higher-lying state S2.

In the transient absorption experiments, a strong signal attributed to the induced absorption from the S1 state is observed in tens of femtoseconds after the excitation of the S2 state. This signal is initially blue-shifting and narrowing, an effect that was attributed to the vibrational cooling of the S1 state [1]. At the same time, direct observation of the population of the carbon-carbon stretching modes (C-C and C=C) has been observed by means of non-linear spectroscopic techniques [2]. Based on these observations we propose a unified description of both the internal conversion between the S2 and S1 states and the subsequent vibrational cooling. The method relies on the secular density matrix theory and the inclusion of the manifold of high-frequency vibrational states into the dynamics. The proposed scheme allows us to obtain relevant transient absorption spectra over several orders of time-scales.

Literature [1] H. H. Billsten, D. Zigmantas, V. Sundström, and T. Polívka Chem. Phys. Lett. 2002, 355, pp. 465-470. [2] T. Buckup, J. Hauer, J. Möhring, and M. Motzkus Arch. Biochem. Biophys. 2009, 483, pp. 219-223.

STENDINIAI PRANEŠIMAI

23


sausio 2-3 d. | Vilniaus universitetasLTStendinis pranešimas

Photoabsorption of acridine yellow and proflavin bound to human serum albumin studied by means of quantum

mechanics/molecular dynamics Kęstutis Aidas1, Jógvan M.H. Olsen2, Jacob Kongsted2 and Hans Ågren3

1 Vilnius University, Lithuania 2 University of Southern Denmark, Odense, Denmark 3 Royal Institute of Technology, Stockholm, Sweden

Attempting to unravel mechanisms in optical probing of proteins, we have performed quantum chemical calculations of two cationic chromophores – acridine yellow and proflavin – bound to different binding sites within human serum albumin [1]. The considered binding sites include the two primary Sudlow's drug binding sites as well as a heme binding site. The computational scheme adopted involves classical molecular dynamics simulations of the ligands bound to the protein and subsequent linear response polarizable embedding density functional theory calculations of the excitation energies. A polarizable embedding potential consisting of point charges fitted to reproduce the electrostatic potential and isotropic atomic polarizabilities computed individually for every residue of the protein was used in the linear response calculations. Comparing the calculated aqueous solution-to-protein shifts of maximum absorption energies to available experimental data [2], we concluded that the cationic proflavin chromophore is likely not to bind albumin at its drug binding site 1 nor at its heme binding site. Although agreement with experimental data could only be obtained in qualitative terms, our results clearly indicate that the difference in optical response of the two probes is due to deprotonation, and not to different binding sites.

Literature [1] K. Aidas, J.M.H. Olsen, J. Kongsted, H. Ågren, J. Phys. Chem. B 117, 2069 (2013). [2] B. Chakraborty, A.S. Roy, S. Dasgupta, S. Basu, J. Phys. Chem. A 114, 13313 (2010).

24



First-principles theory of nonradiative carrier capture via multiphonon emission

Audrius Alkauskas1,2, Qimin Yan2, and Chris G. Van de Walle2

1 Center For Physical Sciences and Technology, Vilnius, Lithuania 2 University of California Santa Barbara, USA

We develop a practical first-principles methodology to determine nonradiative carrier capture coefficients at defects in semiconductors [1]. We consider transitions that occur via multiphonon emission. Parameters in the theory, including electron-phonon coupling matrix elements, are computed consistently using state-of-the-art electronic structure techniques based on hybrid density functional theory. These provide a significantly improved description of bulk band structures, as well as defect geometries and wavefunctions. As a benchmark, we apply our theory to several hole-capturing centers in gallium nitride (GaN) and zinc oxide (ZnO), materials of high technological importance in which the role of defects is being actively investigated. Calculated hole capture coefficients are in an excellent agreement with recent experimental data [2].

Literature [1] A. Alkauskas, Q. Yan, and C. G. Van de Walle, Phys. Rev. B 90, 075202 (2014). [2] M. A. Reshchikov, AIP Conf. Proc. 1583, 127 (2014).

25

Naujametė fi zikos konferencija LTΦ 2015


Generation and parametric amplification of broadband pulses at 2 µm

Giedre Marija Archipovaite, Rytis Butkus

Vilnius University Laser Research Center, Sauletekio al. 10, LT-10223 Vilnius, Lithuania

Ultrashort pulse light sources in the short wave infrared are interesting for different applications such as shorter attosecond pulse generation, ultrafast spectroscopy and explosive or gas detection. Unfortunately, there is no laser gain medium suitable for intense femtosecond pulse generation in this region so the broadband signal shall be generated using nonlinear frequency conversion. Usually three methods of frequency conversion are applied: 1) different frequency generation (DFG) between signal and idler pulses in an optical parametric amplifier (OPA); 2) DFG between different spectral regions of the same broadband pulse; 3) generation of idler pulses in an OPA [1]. The generated broadband signal can later be amplified in an optical parametric chirped pulse amplifier or OPCPA [2].

In this experiment (Fig. 1) parametric amplification and generation of broadband pulses at 2 μm were investigated using OPCPA and DFG methods.

Fig. 1. Generation and parametric amplification of broadband chirped pulses at 2 µm.

Firstly, a parametric chirped pulse amplifier was designed and investigated.

Ti:sapphire oscillator was used to generate femtosecond pulses which were stretched in a bulk SF57 glass up to 10 ps. Pump pulses were generated in two parallel Nd:YAG regenerative amplifiers and a double pass amplifier. The duration of pump pulses was ~50 ps and pulse energy of each channel was ~1,5 mJ. Stretched broadband seed pulses were amplified parametrically in a noncollinear configuration in two subsequent BBO crystals. In order to examine and optimize properties of designed parametric amplifier we measured energy and spectrum of amplified pulses. Pulses were amplified 5·106 times and the efficiency of amplification was 6 %.

26



Broadband pulses at 2 μm were generated in a DFG stage by combining fundamental frequency (FF) of Nd:YAG and pulses amplified in the previously examined parametric amplifier. Pulses at 1,9 – 2,5 μm were achieved and later amplified in a BBO crystal pumped by FF of Nd:YAG double pass amplifier, all the seeded spectra was amplified. At the end we had pulses with spectral bandwidth of ~330 nm, which would result in 22 fs Fourier transform limited pulse and correspond to 3 optical cycles at 2,2 μm. Literature [1] D. Brida, M. Marangoni, C. Manzoni, S. De Silvestri, and G. Cerullo, “Two-optical-cycle pulses in the mid-infrared from an optical parametric amplifier.,” Opt. Lett., 33, 2901–2903 (2008). [2] A. Dubietis, G. Jonusauskas, A.Piskarskas, ”Powerful femtosecond pulse generation by chirped and stretched pulse parametric amplification in BBO crystal”, Opt. Commun., 88, 437 (1992).

27



Collective modes of binary Bose mixtures Jogundas Armaitis, Henk Stoof, Rembert Duine

Utrecht University, Utrecht, The Netherlands

We generalize the Landau-Khalatnikov hydrodynamic theory for uniform binary Bose mixtures at arbitrary temperatures. In particular, we include the spin-drag terms. Therefore, our theory not only describes the usual collective modes of the individual components (e.g., first and second sound), but also results in new collective modes, where all the constituents participate. We study these modes in detail and present their dispersions using thermodynamic quantities obtained from the Bogoliubov theory.

28



Comparison of Spectroscopic and Imaging Performance of Schottky CdTe Medipix3RX and HEXITEC Pixelated Detectors

V. Astromskas1, A. Lohstroh1, E. N. Gimenez2, N. Tartoni2, M. Veale3, P. Sellin1, P. Seller3, M. D. Wilson3

1University of Surrey, Guildford, United Kingdom 2Diamond Light Source, Didcot, United Kingdom

3Rutherford Appleton Laboratory, Didcot, United Kingdom

Many experiments at 3rd generation synchrotron radiation facilities require X-ray detectors that can operate at high frame rates to cope with the high fluxes, > 1x1010 photons s-1. Other experiments require detectors with high energy resolution (< 1 keV) that are able to discriminate between incident, fluorescent and scattered photons. These demanding detector requirements have led to the development of two different small pixel detector systems, HEXITEC and Medipix3RX. In this paper a direct comparison of these two systems will be presented in terms of spectroscopic and imaging performance. The first system was a 0.75mm thick Schottky electron collection CdTe sensor bump-bonded to Medipix3RX ASIC and readout using Merlin readout system that was developed at the Diamond Light Source. The sensor had a 128x128 pixel array with a 110μm pixel pitch. The Medipix3RX ASIC has a 256x256 pixel array with 55μm pitch. The second system to be tested consisted of a 1mm thick Schottky CdTe sensor flip-chip-bonded using a low temperature silver epoxy to the STFC HEXITEC read-out ASIC. The sensor consists of an 80x80 pixel array on a 250μm pitch. Each of the pixels has identical readout circuitry and produces high resolution spectra in each of the 6,400 pixels. The spectroscopic performance of both of the detectors was tested using 241 Am radioactive source. The results showed HEXITEC detector having higher energy resolution of 1.1keV at 59.5keV. The imaging performance was tested using modulation transfer function (MTF). The results showed that Medipix3RX detector has better spatial resolution than HEXITEC detector. Also, results from identification of transition metals using HEXITEC detector are presented.

Study of the initial state in the relativistic heavy-ion collisions

Tomas Babelis1 and Karolis Tamošiūnas1

1Institute of Theoretical Physics and Astronomy, Vilnius University, Goštauto g. 12, 01108 Vilnius, Lithuania

For a first few milliseconds after the Big Bang the universe was incredibly dense plasma, which consisted of free quarks and gluons. This phase of matter is called quark-gluon plasma (QGP). Similar conditions are repeated in the heavy-ion collision experiments at sufficiently high energy. QGP cannot be detected directly, thus its properties must be inferred from the momentum and multiplicity distributions of the formed particles. The purpose of this study is to find the hydrodynamic parameters of the initial state of the heavy-ion collision using experimental data of rapidity distribution of produced particles. Landau hydrodynamics is an approximate and analytic solution of the relativistic hydrodynamics for the evolution of the QGP. The rapidity distribution of produced particles in the center-of-mass system to be [1]:

𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 ∝ 𝑒𝑒𝑒𝑒𝑒𝑒√(𝑑𝑑𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏2 − 𝑑𝑑2)

where 𝑑𝑑𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 = ln(√𝑆𝑆𝑁𝑁𝑁𝑁/𝑚𝑚𝑁𝑁) is the beam rapidity, m-mass of the nucleon, √𝑆𝑆𝑁𝑁𝑁𝑁 - c.m. energy per nucleon. It will be shown, that experimentally known rapidity and transverse angle multiplicity distributions can be direclty connected to the initial longitudinal thickness and initial pressure gradients [2]. Therefore, having Event-by-Event data of particle multiplicities distributions 𝑑𝑑2𝑑𝑑/𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 allows us to find initial state parameters in the relativistic heavy-ion collision.

Literature [1] C.Y. Wong, Phys. Rev. C 78, 054902 (2008) arXiv: 0808.1294 [hep-ph]. [2] K. Tamošiūnas, Longitudinal scaling of elliptic flow in Landau hydrodynamics, arXiv:1106.4839v2, (2011), http://arxiv.org/abs/1106.4839

29



Study of the initial state in the relativistic heavy-ion collisions

Tomas Babelis1 and Karolis Tamošiūnas1

1Institute of Theoretical Physics and Astronomy, Vilnius University, Goštauto g. 12, 01108 Vilnius, Lithuania

For a first few milliseconds after the Big Bang the universe was incredibly dense plasma, which consisted of free quarks and gluons. This phase of matter is called quark-gluon plasma (QGP). Similar conditions are repeated in the heavy-ion collision experiments at sufficiently high energy. QGP cannot be detected directly, thus its properties must be inferred from the momentum and multiplicity distributions of the formed particles. The purpose of this study is to find the hydrodynamic parameters of the initial state of the heavy-ion collision using experimental data of rapidity distribution of produced particles. Landau hydrodynamics is an approximate and analytic solution of the relativistic hydrodynamics for the evolution of the QGP. The rapidity distribution of produced particles in the center-of-mass system to be [1]:

𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 ∝ 𝑒𝑒𝑒𝑒𝑒𝑒√(𝑑𝑑𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏2 − 𝑑𝑑2)

where 𝑑𝑑𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 = ln(√𝑆𝑆𝑁𝑁𝑁𝑁/𝑚𝑚𝑁𝑁) is the beam rapidity, m-mass of the nucleon, √𝑆𝑆𝑁𝑁𝑁𝑁 - c.m. energy per nucleon. It will be shown, that experimentally known rapidity and transverse angle multiplicity distributions can be direclty connected to the initial longitudinal thickness and initial pressure gradients [2]. Therefore, having Event-by-Event data of particle multiplicities distributions 𝑑𝑑2𝑑𝑑/𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 allows us to find initial state parameters in the relativistic heavy-ion collision.

Literature [1] C.Y. Wong, Phys. Rev. C 78, 054902 (2008) arXiv: 0808.1294 [hep-ph]. [2] K. Tamošiūnas, Longitudinal scaling of elliptic flow in Landau hydrodynamics, arXiv:1106.4839v2, (2011), http://arxiv.org/abs/1106.4839

30



Quantum mechanical study of the proline molecule

fragmentation by low energy electrons

Laura Baliulyt1,2, Jelena Tamulien2

1Vilnius University, Faculty of Natural Sciences, M.K. Ciurlionio st. 21/27, LT-03101 Vilnius, Lithuania

2Vilnius University, Institute of Theoretical Physics and Astronomy, A. Gostauto 12, LT-01108 Vilnius, Lithuania

The studies of the amino acid damages resulted from the influence of ionizing radiation

are very important. The majority of the above damages are not usually due to the primary

high-energy radiation but it results from the effect of the secondary low-energy charged

particles produced in the course of ionization [1].

The structure of the most stable conformer of proline, its fragment energies of

appearance and thermodynamic parameters have been studied using density functional

theory (DFT) B3LYP method and cc-pVTZ basis set. In this research experimentally

measured mass-spectrum of proline has been used. Scientists from Institute of Electron

Physics, Ukraine, measured this spectrum. The peaks positive charged ions which m=28, 41,

43, 68 and 70 a.m.v. are the most noticeable in the proline mass-spectrum. The main goal of

our studies was to determine energetically favourable proline fragmentation reactions and

identified fragments obtained. In order to model the fragmentation processes, the possible

fragment cations, anions and fragments with a zero charge both with and without geometry

optimization have been analyzed to predict the dissociation energy on the fragmentation

processes. The fragment identified and calculated appearance energies (in eV) and reaction

rate (s-1) after are listed in Table 1.

Table 1. Calculated appearance energies (in eV) and reaction rate (s-1) for the C2H4,C2H3N,

C2H5N, C4H6N and C4H8N fragments formed from the proline molecule Fragments Fragmentation reactions Appearance energies, eV Reaction rate, s

-1

C2H4 (m=28 a.m.v.) C5H9NO2 + e C2H4

+ + C3H5NO2

0 + 2e 11.99 6.76E+13

C2H3N (m=41 a.m.v.) C5H9NO2 + e C2H3N+

+ C3H6O2- + e 10.13 7.03E+13


+ C3H4O20 + 2e 10.18 6.86E+13


+ CH5O2- + e 11.63 6.39E+13


+ CHO20 + 2e 8.68 6.61E+13

Literature

[1] S. Cristoni, L.R. Bernardi. Mass. Spectr. Rev. 22, 369 (2003).

31



Investigation of Ultrashort Pulse All-in-fiber Oscillator Using Different Dispersion Chirped Fiber Bragg Gratings

Tadas Bartulevičius1*, Saulius Frankinas1,2, Rokas Danilevičius1,2, Nerijus Rusteika1,2

1 EKSPLA, Ltd., Savanoriu Ave. 231, Vilnius, Lithuania 2 Department of Laser Technology, Center for Physical Sciences & Technology, Savanoriu

Ave.231, Vilnius, Lithuania *[email protected]

Fiber lasers are extensively applicable in variety of fields such as medical diagnostics, laser material processing, imaging, spectroscopy and scientific research. High power, high repetition rate ultrashort pulse fiber lasers are usually realized using chirped pulse amplification (FCPA) technique. However, it is necessary to choose system parameters correctly to suppress nonlinear effects which are very significant comparing to solid state laser systems and scale rapidly with higher optical intensities causing spectral distorsions and reduced pulse contrast at the system output. Final pulse duration and spectrum could be strongly affected by the seed source output parameters.

Passively mode-locked all-in-fiber oscillators operating at average soliton pulse regime are simple, stable and reliable seed sources for FCPA. The pulse duration of such source could be easily controlled choosing Chirped Fiber Bragg Grating (CFBG) with correct dispersion value in the laser resonator. In previous work, we demonstrated FCPA system with all-in-fiber seed source which generated 2 ps pulses. This system lacked of pulse contrast at the output without using additional nonlinear phase compensation components. One of the solutions of such system improvement is to generate shorter pulses in fiber oscillator. The purpose of this work was to find the main parameters of CFBGs used in the seed source in order to generate broad spectrum transform-limited sub-picosecond and femtosecond pulses. We have theoretically and experimentally investigated specially designed and manufactured CFBGs with different dispersion values. Detailed calculations compared with experimental results will be presented at the conference.

References [1] S. Frankinas, R. Danilevičius, N. Rusteika, “High Power Femtosecond CPA System With TOD Compensating Chirped Fiber Bragg Grating Stretcher”, 16th International Conference “Laser Optics 2014”.

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Damage probability analysis as a tool to identify defects within individual layers of thin film coated optics

Gintarė Batavičiūtė, Linas Smalakys, Egidijus Pupka and Andrius Melninkaitis1 1Vilnius University, Laser Research Center, Vilnius, Lithuania

Nanosecond laser induced damage on dielectric materials is usually caused by nanometer sized defects, created during manufacturing processes. As a rule of thumb, most of the embedded defects reduce laser-induced damage threshold (LIDT) of produced component. However, minimization of defect density, does not always lead to the improvement of LIDT. Screening factors, such as interference effects, should also be taken into account. So far, there is a lack of scientific tools and techniques that could determine if damage was initiated within the coating or at the coating - substrate interface. Thus, the goal of this study is to present a new metrological approach, capable of identify layers, containing defects with the lowest LIDT in complex multilayer optics.

The role of defects, inherited in optical elements during polishing procedure and deposition of dielectric coatings, is interpreted in terms of laser induced damage probability [1]. Changes of damage threshold behavior are observed in bare fused silica substrate, monolayer thin films (silica and hafnia) and highly reflective multilayer HfO2/SiO2 coating with central wavelength at 355 nm. All samples are irradiated under UV (355 nm, 4.8 ns) nanosecond laser pulses at different angles of incidence (00 and 450) and different polarization (s, p). Then, statistical damage probability models are constructed for experimental data approximation. Effects of light intensification by standing waves within multilayer coatings [2] and localization of the defects (surface, interface and bulk) are considered as key factors within presented study.

Primary results show that manipulation of irradiation conditions combined with theoretical modeling could aid in identifying origin of LIDT limiting defects. Substrate defects were determined as the limiting source in the case of uncoated fused silica sample and both SiO2 and HfO2 thin films. Presented results also imply that damage threshold of highly reflective multilayer HfO2/SiO2 coating with central wavelength at 355 nm might vary for the shallow and deep layers of HfO2 within a mirror. Both assumptions will be discussed in details in the presented poster.

Literature [1] ISO21254-1, “Determination of laser-induced damage threshold of optical surfaces part 1: 1-on-1 test," Determination of laser-induced damage threshold of optical surfaces - Part 1: 1-on-1 test (2011).

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Study of magnetic and structural properties of cobalt-manganese ferrite nanoparticles obtained by

mechanochemical synthesis

V.Bėčytė1, K.Mažeika1, T.Rakickas1

1 Center for Physical Sciences and Technology, Savanoriu 231, LT- 02300, Vilnius, Lithuania.

Nanosized transition metal oxides MFe2O4 (M= Co, Ni, Mn) are widely investigated because of its unique optical, magnetic and sorption properties. Such oxide-based magnetic nanoparticles have a great potential for technological applications: high

density data storage, microwave devices etc.[1] Lately, however, magnetic nanoparticles have been extensively studied because of their possible applications in medicine: cancer therapy by hyperthermia, controlled drug delivery, cell separation and magnetic resonance imaging [2-3].

This study presents the research done on nanoparticles of CoFe2O4 and MnFe2O4 obtained by mechanochemical synthesis using high-energy ball mill, solid metal salts as precursor and sodium chloride NaCl as a growth agent for further biomedical applications.

Mössbauer spectroscopy (Fig.1), magnetization studies, atomic force microscopy (AFM) and X-ray studies were used to determine the properties of the nanoparticles depending on the conditions of the synthesis. It was found that it is possible to control particle size which varied from 4 nm up to ~10 nm without and with addition of growth agent respectively.

Literature [1] Faquan Yu, Lei Zhang, Yongzhuo Huang,Kai Sun, Allan E. David, Victor C.Yang, Biomaterials 31,5842 (2010) [2] M. Wang, M. Thanou, Pharmacological Research 62, 90 (2010) [3] Eduardo Ruiz-Hernandez, Alejandro Baeza, Maria Vallet- Regi, ACSnano 5,1259 (2010).

Fig. 1. The Mössbauer spectra a) CoFe2O4 synthesized without growth agent; b) CoFe2O4 synthesized with growth agent; c) MnFe2O4 synthesized without growth agent

34



Vibronic coherence in photosynthetic molecular complexes

Vytautas Butkus1,2, Andrius Gelzinis1,2, Franklin D. Fuller3, Jennifer P. Ogilvie3, Leonas Valkunas1,2 and Darius Abramavicius1

1 Faculty of Physics, Vilnius University, Vilnius, Lithuania 2 Center for Physical Sciences and Technology, Vilnius, Lithuania

3 Department of Physics and Biophysics, University of Michigan, Ann Arbor, Michigan, USA

Coupling between electronic excitations and intramolecular vibrations in molecular systems known as vibronic coupling is responsible for a host of phenomena, observed by linear and nonlinear spectroscopic techniques. For example, these include vibrational wave-packet motion, long-lived coherences, vibrational anisotropy beats or polaron formation. For many of those, exciton-vibrational resonances, most conveniently seen by the 2D electronic spectroscopy, are very important.

In this work, we report the observation of vibronic coherence in the reaction center of Photosystem II and show, that presence of quantum-mechanically mixed coherences of electronic-vibrational nature may play a functional role in enhancing energy transfer, i.e. increasing the rate of charge transfer event in photosynthetic membrane [1,2]. From supporting theoretical calculations, we are also able to discuss the general properties of exciton-vibrational interference in molecular complexes: (i) classify and define the typical spectroscopic features of vibronically coupled molecules, (ii) separate the cases, when the long-lived coherences should be expected, (iii) define when the complete exciton-vibrational mixing occurs and (iv) when separation of purely excitonic and vibrational coherences is possible [3].

Literature [1] F. D. Fuller, J. Pan, A. Gelzinis, V. Butkus, S. S. Senlik, D. E. Wilcox, C. F. Yocum, L. Valkunas, D. Abramavicius, J. P. Ogilvie, Nature Chem. 6, 706-711 (2014) [2] E. Romero, R. Augulis, V. I. Novoderezhkin, M. Ferretti, J. Thieme, D. Zigmantas, R. van Grondelle, Nature Phys. 10, 676-682 (2014) [3] V. Butkus, L. Valkunas, D. Abramavicius. J. Chem. Phys. 140, 034306 (2014)

35



Magnetic resonance imaging of superparamagnetic iron oxide nanoparticles distribution in vivo

Eglė Daugėlaitė1,2, Marius Stalnionis1,2

1Laboratory of Biomedical Physics, National Cancer Institute, LT-08406 Vilnius, Lithuania

2Laser Research Center, Vilnius University, LT-10223 Vilnius, Lithuania

Fe3O4 superparamagnetic iron oxide nanoparticles (SPIONs) represent a novel class of negative contrast magnetic resonance imaging (MRI) agents, that produce significant reduce in T2-weighted signal [1]. These nanoparticles are very promising non-invasive tool in biomedical imaging and clinical diagnosis [2]. An animal model can be studied in order to evaluate migration and accumulation of magnetic nanoparticles in vivo and to optimize imaging properties. In this study, MRI images were taken over 3 weeks after intravenous or intramuscular administration of SPIONs to Wistar rats. Later, the images were analyzed for the distribution. The uptake and clearance results suggest that Fe3O4 could be used as contrast agent for MRI and also used as a platform for designing more specific imaging tracer..

Literature [1] J. Haegele, R.L. Duschka, M. Graeser, C. Schaecke, N. Panagiotopoulos, K. Ludtke – Buzug, T.M. Buzug, J. Barkhausen, F.M. Vogt. Magnetic particle imaging: kinetics of the intravascular signal in vivo, International Journal of Nanomedicine 9 4203-4209 (2014). [2] Z.R. Stephen, F.M. Kievit, M. Zhang. Magnetite nanoparticles for medical MR imaging, Materials today 14(7-8) 330-338 (2011)

36



Thermal neutron detection using thin PEN film with layer of FeB micropatricles

Jevgenij Garankin, Artūras Plukis, Elena Lagzdina

Center for Physical Sciences and Technology Savanorių pr. 231, LT-02300 Vilnius, Lithuania

Poly(ethylene 2,6-naphthalate) (PEN) is promising as the new plastic scintillator [1]. In this study thin PEN film and FeB microparticles were used for thermal neutron detection. 10B isotope has a neutron capture cross section of 3835 barns and exists in a natural abundance of approximately 20%. FeB microparticles were used to create 1.5 MeV α particles from B(n,α) reaction. α particles from B(n,α) reaction were detected by scintillation in PEN and PMT pulses were collected and analyzed. It was found, that a small quantity of 1.5 MeV α particles from thermal neutron reaction can be detected in strong background of neutron, gamma rays and recoil protons.

References [1] N. Nakamura, Y. Shirakawa, etc. Evidence of deep-blue photon emission at high efficiency by common plastic Europhysics Letters Vol. 95 2011: 22001.

37



Yeast cell encapsulation with the polypyrrole

Andrius Garbaras1, Eivydas Andriukonis1, Vidmantas Remeikis2 ir Arūnas Ramavaičius1

1 Laboratory of NanoBioTechnology, Institute of Semiconductor Physics, State Research Institute Centre for Physical and Technological Sciences, A. Gostauto g. 11,

LT-01108 Vilnius, Lithuania 2 Laboratory of Mass Spectrometry, Institute of Physics, State Research Institute Centre

for Physical and Technological Sciences, Savanoriu av. 231, LT – 02300 Vilnius, Lithuania

Baker's yeast cells (Saccharomyces cerevisiae) before and after encapsulation with the polypyrrole were measured by the isotope ratio mass spectrometry. Isotopically labelled pyrolle was used, with the δ15N ratios ranging from 50 to 500 ‰. Using isotope ratio mixing model, it was determined the amount of the polypyrrole sticking to the yeast cell.

38



Generation of Third, Fifth and Seventh Harmonics in Bulk Solids with Intense Mid-Infrared Pulses

Nail Garejev1, Ieva Gražulevičiūtė1, Vytautas Jukna2, Donatas Majus1, Gintaras Tamošauskas1, Gintaras Valiulis1, Arnaud Couairon2, Audrius Dubietis1

1Department of Quantum Electronics, Vilnius University, Saultekio Ave. 9, Building 3, LT-10222 Vilnius, Lithuania

2Centre de Physique Theorique, CNRS, Ecole Polytechnique, F-91128 Palaiseau, France

E-mail: [email protected],

Intense ultrashort laser pulses provide a unique way to study laser-matter interactions in transparent dielectric media with high temporal resolution, especially in the emerging field of ultrafast mid-infrared nonlinear optics. One of the important applications of such pulses is the measurement of higher-order optical nonlinearities and understanding their role in harmonics generation processes [1].

In this Contribution we present the results on the third (TH) and fifth harmonic (FH) generation with two optical-cycle, carrier-envelope phase-stable pulses at 2 µm. Harmonics were generated in CaF2 crystal of variable thickness. The harmonics spectra, energy and conversion efficiency were measured as a function of propagation length and input pulse intensity, which was varied up to 15 TW / cm2. The cross-correlation measurements directly retrieve a double-peaked temporal structure of TH radiation, consisting of free and driven components without the splitting of the driving pulse at fundamental frequency. Detailed measurements of TH and FH spectra as functions of propagation distance, combined with supporting numerical simulations, have shown that FH is generated solely via four-wave mixing between the fundamental and TH, 5ω = 3ω + ω + ω, without any detectable contribution of six-wave mixing due to the quintic nonlinearity in the process [2]. In the second experiment, we have also investigated the generation of TH, FH and seventh harmonic (SH) with 100 fs pulses at 2.4 µm. The first results show that the energy of SH oscillates in phase with the energy of TH as a function of propagation length, suggesting a cascaded nature of SH generation process as well.

This research was funded by the European Social Fund under the Global Grant measure, grant No. VP1-3.1- ŠMM-07-K-03-001.

Literature [1] M. Kolesik, E. M. Wright, J. V. Moloney, Opt. Lett. 35, 2550 (2010). [2] N. Garejev, I. Gražulevičiūtė, D. Majus, G. Tamošauskas, V. Jukna, A. Couairon, and A. Dubietis, Phys. Rev. A 89, 033846 (2014).

39



Self-reconstructing, carrier envelope phase-stable spatiotemporal light bullets

I. Gražulevičiūtė1, R. Šuminas1, D. Majus1, G. Tamošauskas1, N. Garejev1, V. Jukna2, A. Couairon2, D. Faccio3, A. Dubietis1

1 Vilnius University, Vilnius, Lithuania 2 Ecole Polytechnique, Palaiseau, France

3 Heriot-Watt University, Edinburgh, United Kingdom

Self-focusing and filamentation of intense femtosecond laser pulses in transparent solids in the regime of anomalous group velocity dispersion leads to formation of non-diffracting and non-dispersing self-compressed ultrashort pulsed beams – light bullets [1]. However, there still remain open fundamental issues concerning the physical interpretation of these bullets [2]. In this Contribution, we present an extensive experimental and numerical analysis of spatiotemporal light bullets generated by filamentation of 100 fs, 1.8 μm laser pulses in sapphire crystal. The complete propagation dynamics in four dimensions (x, y, z, t) was recorded by means of spatially-resolved cross-correlation technique. These measurements revealed that the input Gaussian wave packet transforms into a Bessel-like beam, consisting of a high-intensity core which carries the self-compressed, few optical cycle pulse and delocalized, ring-shaped low-intensity periphery. The high-intensity core maintains its localization over several diffraction and dispersion lengths in the nonlinear medium, but broadens in space and time during free space propagation due to strong space-time coupling, which is a distinctive property of conically shaped wave packets [3]. The delocalized periphery is shown to be an important integral part of the light bullet, ensuring its robustness to external perturbations. Our measurements demonstrate that the central core of the bullet, after being completely blocked by the beam stopper, self-reconstructs and fully restores its spatial and temporal dimensions. Finally, we show that the light bullet maintains stable carrier-envelope phase, as verified by f-2f interferometric measurements. This research was funded by the European Social Fund under the Global Grant measure, grant No. VP1-3.1-SMM-07-K-03-001. Literature [1] M. Durand, A. Jarnac, A. Houard,Y. Liu, S.Grabielle,N. Forget, A. Durecu, A. Couairon, A. Mysyrowicz, Phys. Rev. Lett. 110, 115003 (2013). [2] D. Majus, G. Tamošauskas, I. Gražulevičiūtė, N. Garejev, A. Lotti, A. Couairon, D. Faccio, A. Dubietis, Phys. Rev. Lett. 112, 193901 (2014). [3] D. Faccio, M. Clerici, A. Averchi, A. Lotti, O. Jedrkiewicz, A. Dubietis, G. Tamošauskas, A. Couairon, F. Bragheri, D. Papazoglou, S. Tzortzakis, P. Di Trapani, Phys. Rev. A 78, 033826 (2008).

40



AdS/CMT correspondence and field theory interpretations

Simonas Grubinskas

Utrecht University, Utrecht, The Netherlands

Using the AdS/CFT (anti-de Sitter / conformal field theory) correspondence it is possible to obtain properties of certain quantum field theories pertaining to high-energy physics. The statement of the AdS/CMT (condensed matter theory) correspondence is that the calculations of high-energy physics might be applicable to low-energy physics as well, e.g., to conductors or to Bose gases. While calculations in curved AdS space-time can provide some information about certain field theories, there is no systematic way of figuring out what exactly those field theories are. In our work, we have modeled the latter quantum field theories and we have calculated their properties, such as the self-energy and the conductivity, while comparing the results to predictions from AdS calculations. The resulting field theory interpretation leads to a better understanding of the underlying structure of AdS/CMT.

Literature [1] V.P.J. Jacobs, S. Grubinskas and H.T.C. Stoof, Towards a field theory interpretation of bottom-up holography. Submitted to JHEP.

41



Cellular uptake and cytotoxicity of photoluminescent Au-BSA nanoclusters in breast cancer cells

Greta Jarockytė1, Marija Matulionytė1,2

1 Biomedical Physics Laboratory of National Cancer Institute, Baublio 3B, LT08406, Vilnius, Lithuania.

2 Biophotonics group of Laser Research Centre, Vilnius University, Saulėtekio 9, c.3, LT-10222, Vilnius, Lithuania

In recent years, the use of nanoparticles in biomedical research has gathered momentum. To date, researchers have developed different types of luminescent nanomaterials; however, toxicity limits most of their practical applications. A few years ago a new class of photoluminescent nanoparticles – protein stabilized gold nanoclusters (Au-BSA NCs) – emerged. Due to high biocompatibility and low toxicity Au-BSA NCs are very promising as biolabels for cancer diagnostics.

Au-BSA NCs were synthesized according to previously reported procedure1 with slight modifications. Cellular uptake was investigated incubating MCF-7 breast cancer cells with 56 mg/ml of Au-BSA NCs for 24h at 37°C. After 24h of incubation, Au-BSA NCs were localized in vesicles, which were mostly observed near the nucleus. Au-BSA NCs have not accumulated in the nucleus of cell.

In order to compare the uptake of Au-BSA NCs with the uptake of BSA alone, MCF-7 breast cancer cells were treated with BSA conjugated with Alexa Fluor 488 organic dye (BSA-Alexa). Cells were incubated with 0,01 mg/ml of BSA-Alexa under the same conditions as described for the Au-BSA NCs. The accumulation of Au-BSA NCs and BSA-Alexa was observed using a fluorescence confocal microscope. The accumulation of BSA-Alexa in cells was similar to the accumulation of Au-BSA NCs. BSA is known to accumulate in cells via endocytosis2 and gold nanoclusters inside the protein appear to cause no change in its uptake mechanism.

Toxicity of Au-BSA NCs was investigated using XTT cell viability assay. Au-BSA NCs have no significant influence on viability of MCF-7 cancer cells: the viability of cells remains approximately 100% after 24h of incubation.

Literature [1] J. Xie, Y. Zheng, and J.Y. Ying. Protein-Directed Synthesis of Highly Fluorescent Gold Nanoclusters. J. Am. Chem. Soc., 131 (3): p. 888–889 (2009). [2] R. Yumoto, H. Nishikawa, M. Okamoto, H. Katayama, J. Nagai, M. Takano, Clathrin-mediated endocytosis of FITC-albumin in alveolar type II epithelial cell line RLE-6TN, Am. J. Physiol. Lung Cell Mol. Physiol. 290 (5): p. 946–955 (2006).

42



Peculiarities of the PPKTP optical parametric oscillator pumped by 1064 nm radiation

Karolis Jurkus, Daniel Žitkovskij, Vygandas Jarutis ir Valerijus Smilgevičius

Vilnius University Laser Research Center, Vilnius, Lithuania

In this work we present results of investigation of PPKTP optical parametric oscillator pumped by Nd:YAG laser radiation. In [1] it was shown that the doubly resonant OPO output energy drastically depends on the cavity length and has periodically changeable maxima/minima. This phenomenon was explained as interaction of signal and idler waves in a doubly resonant OPO cavity. The same situation arises in all doubly resonant OPOs. The main attention in our research was devoted to temperature stability of the OPO output radiation because wavelengths of signal and idler waves change by tuning OPO crystal temperature which alters OPO resonator quality.

We investigate PPKTP OPO pumped by radiation of commercial microchip laser STA-01 (UAB “STANDA): wavelength – 1064 nm, pulse energy – 300 µJ, pulse

duration 3,2 ns, repetition rate – 1 kHz. OPO resonator consists of two mirrors: concave with curvature radii 30 mm (HR 1550 nm, HT 1064 nm) and output flat mirror (HR 1064 nm, 75% T 1550 nm). Resonator length was 19 mm. Nonlinear crystal was periodically poled KTP crystal with poling period of 35.55 µm, crystal length – 10 mm.

OPO generation threshold was 20 µJ, and maximum energy for 220 µJ pump was 100 µJ which signifies 45% conversion efficiency. In

Fig.1 the OPO output power dependence on the PPKTP crystal temperature is presented. The experimental results are in good agreement with theoretical calculations.

Literature: [1] G. Aristholm, E.Lippert, G.Rustad and K.Stenersen, Optics Letters 25, 1654 (2000).

43



PHOTOSTABILITY AND TOXICITY OF CdSe HYDROPHILIC QUANTUM DOTS IN MEDIA WITH FRESHWATER ALGAE

Agnė Kalnaitytė, Saulius Bagdonas

Department of Quantum Electronics, Faculty of Physics, Vilnius University, Lithuania

Quantum dots (QDs) - semiconductor particles of nanometre size - have been widely used as photoluminescent agents in the fields of medicine, biology and material science. With the ever-increasing applications of nanotechnology, nanoparticles might spread through various habitats and find their way into the aquatic environment, yet their potential risks for biosystems remain unclear. Freshwater algae are among the species commonly used as model organisms to assess the toxicity of QDs.

In this study, absorption, steady state spectroscopy and microscopy measurements on CdSe-COOH quantum dots (an emission peak at 518 nm) in biological model environment were performed. Spectral properties, photostability and toxicity of QDs in the presence of freshwater microalgae Scenedesmus were investigated.

Fig. 1 a)Photoluminescence spectra of quantum dots (λex=300nm) in aqueous media (solid line) and in media with microalgae (dash-dot line), as well as one day after 1 hour exposure to the blue light in aqueous media (dash line) and in media with microalgae (short dash line). b) The autofluorescence intensity of algae (at 682nm maximum) after a month, “c” – relative concentration of microalgae (used in samples with QDs).

Aqueous medium induced a time-related hypsochromic shift of the photoluminescence (PL) band of CdSe quantum dots (from 518 nm to 380 nm), but this shift was not observed in the samples with microalgae at the initial days (Fig. 1a). Since light is one of external factors that could affect both stability and toxicity of QDs, the samples were exposed to the blue diode light (404±9 nm (FWHM), 90 mW/cm2) for an hour. The light-induced changes in photophysical properties of CdSe QDs, such as decreased intensity and the spectral broadening of a PL band towards shorter wavelengths, which were

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observed immediately after the exposure, mimicked those occurring in aqueous medium. These spectral changes can be related with the structural degradation of QDs.

Irradiation with a blue diode caused reversible short-term photobleaching of microalgae fluorescence at 682 nm. The light exposure also had a suppressive effect on growth of microalgae population. However, the average algae population in samples with QDs observed by spectroscopic measurements was reaching about 25% of the control after a month (Fig. 1b). The damaged cells were confirmed in the samples with CdSe QDs taken by means of the fluorescence microscopy, but not in the samples without QDs, implying that the fragmentation of QDs induced a toxic effect on algae cells.

45



Lévy flights in non-homogeneous media and 1/f noise

Rytis Kazakevičius1 ir Julius Ruseckas1

1 Institute of Theoretical Physics and Astronomy, Vilnius University, Vilnius, Lithuania

Complex dynamical systems exhibiting signals with power-law tails can be described by Langevin equations driven by Lévy stable noise. If system behavior depends only on large noise fluctuations. The Lévy process constitute the most general class of stable processes while the Gaussian process is their special case. Lévy flight is a generalization of the Brownian motion which describes the motion of small macroscopic particles in a liquid or a gas experiencing unbalanced bombardments due to surrounding atoms. The Brownian motion mimics the influence of the “bath'' of surrounding molecules in terms of time-dependent stochastic force which is commonly assumed to be white Gaussian noise. That postulate is compatible with the assumption of weak interactions with the bath. In contrast, the Lévy motions describe results of strong collisions between the particle and the surrounding environment. Lévy non-Gaussian processes can also be trace back to the non-homogeneous structure of the environment, in particular, fractal or multi-fractal [1]. Lévy flights can lead to anomalous diffusion in many physical systems: as an example we can point out anomalous diffusion of Na adatoms on solid Cu surface [2], anomalous diffusion of a gold nanocrystal, adsorbed on the basal plane of graphite.

A class of nonlinear stochastic differential equations providing the power-law behavior of spectra, including 1/f noise, and the power-law distributions of the probability density has been proposed [3]. The equations with the Gaussian noise arise as a special case when the index of stability λ = 2. We investigate numerically the frequency range where the spectrum has 1/f form and have shown that this frequency range depends on power-law exponent in steady state distribution as well as on the index of stability. We expect that this generalization may be useful for describing 1/f fluctuations in the systems exhibiting anomalous diffusion.

Literature [1] T. Srokowski, Phys. Rev E 78, 031135 (2008). [2] W. D. Luedtke and U. Landman, Phys. Rev. Lett. 82, 222222 (1999). [2] R. Kazakevičius and J. Ruseckas, Physica A 411, 95 (2014).

46



Photoluminescence study of excitonic Mott transition in coupled InGaAs quantum wells

Gabija Kiršanskė, Raphaël Daveau, Peter Lodahl, and Søren Stobbe

Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, DK-2100 Copenhagen, Denmark

In this work a photoluminescence signature of the excitonic Mott transition in coupled InGaAs wells is demonstrated. A coupled quantum well is composed of two quantum wells separated by a thin barrier that allows coupling of an electron and a hole residing in adjacent wells, thus supporting spatially indirect excitons with a small electron-hole overlap. Consequently, the radiative lifetime of an indirect exciton can be orders of magnitude longer than that of direct excitons. By varying external parameters, e.g., density or temperature, the insulating exciton gas can undergo a Mott transition to a conducting electron-hole plasma. It has been demonstrated in a multiple GaAs quantum well system by probing the excitonic population in time domain [1]. In this work the phase transition from indirect excitons to electron-hole plasma was studied as a function of carrier density and electric field. The transition occurred gradually as can be seen in Fig. 1 where the bound exciton population dominates at low excitation power and is slowly taken over by the electron-hole plasma with increasing excitation power. Additionally, the transition was studied as a function of applied electric field at constant excitation intensity and temperature, providing an exceptionally clear demonstration of the excitonic Mott transition in photoluminescence.

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Figure 1.Photoluminscence spectra of indirect excitons recorded at different excitation powers at T=8 K. A gradual transition from an insulating state of excitons (blue) into an electron-hole plasma (red) occurs with increasing carrier density. Literature

[1] R. A. Kaindl, M. A. Carnahan, D. Hägele, R. Lövenich and D. S. Chemla, Nature 423, 734-738 (2003).

47



Search for tt resonances with the CMS-detector

Vilius Kripas, Daniel Gonzalez, Johannes Haller, Roman Kogler, Thomas Peiffer,

Jochen Ott, Emanuele Usai, Ivan Marchesini

University of Hamburg, Institute for experimental physics

A search for resonances in tt production at the LHC is presented. The top quark is the

heaviest known quark and there are many theoretical extensions of the SM which

predict tt production via the exchange of a heavy new particle. For high resonance

masses the decay products of the top quarks do not occur as isolated leptons or

individual jets due to the high Lorentz boost. Therefore, special analysis methods

including jet substructure algorithms and specific isolation criteria are used. In this talk

the methods for the selection of top quark pairs in the lepton+jets decay channel are

presented. The use of advanced top-tagging and b-tagging algorithms within jet

substructure is discussed. The invariant mass distribution of the tt system is used to

determine exclusion limits for tt resonances in various models of new physics.

48



Influence of interface roughness in quantum cascade lasers

Kasparas Krivas, Andreas Wacker, Martin Lindskog, David Winge

Lund University, Lund, Sweden

Quantum cascade lasers (QCLs) are solid state structures that can lase in mid-infrared and terahertz range. Since the first demonstrated operating device in 1994 [1] these lasers attracted a lot of attention and were developed to work at room (mid IR lasers) temperature. However, not every phenomenon is well understood. The influence of interface roughness (IFR) is one of them. As shown by C. Deutsch et al. [2], IFR is important phenomenon affecting performance of the QCL.

This work investigates the influence of IFR on performance of QCLs using the program documented in Ref [3]. The program is based on a model developed using non-equilibrium Green's function theory. IFR is described by an autocorrelation function with parameters η (standard deviation) and λ (correlation length). Interface roughness enters the simulation through self-energies as Fourier transform of the autocorrelation function. The Fourier transform of the autocorrelation function, that was used in this work, is:

Here I present simulation results, that demonstrate the influence of interface roughness on QCLs performance. Two-well [4] and three-well [5] QCL designs are used. Simulations were performed for increased IFR and compared with the reference simulations (IFR is as reported in the Ref [4] and [5]).

It was observed that current increases as a superposition of contributions from different interface roughness. This contribution is sensitive to the autocorrelation function and that can be used to obtain some insight about underlying phenomena.

Literature

[1] J. Faist, F. Capasso, D.L. Sivco, C. Sirtori, A.L. Hutchinson, A.Y. Cho, Science (New York, N.Y.) 264 (5158), 553 (1994) [2] C. Deutsch, H. Detz, T. Zederbauer, A.M. Andrews, P. Klang, T. Kubis, G. Klimeck, M.E. Schuster, W. Schrenk, G. Strasser, K. Unterrainer, Optics express 21, 7209 (2013) [3] A. Wacker, M. Lindskog, D. Winge, IEEE Journal of Selected Topics in Quantum Electronics 19 (5), 1 (2013) [4] G. Scalari, N. Hoyler, M. Giovannini, J. Faist, Applied Physics Letters 86 (18), 181101 (2005) [5] S. Kumar, Q. Hu, J.L. Reno, Applied Physics Letters 94 (13), 131105 (2009)

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λη=qf

49



Study of Artificial Light Harvesting Antennae by Quantum Chemical Methods

Svetlana Malickaja1, Mindaugas Macernis1,2, Juozas Sulskus1, Leonas Valkunas1,2

1 Department of Theoretical Physics, Faculty of Physics, Vilnius University, Vilnius, Lithuania

2 Center for Physical Sciences and Technology, Vilnius, Lithuania

Carotenoids play a crucial role in the energy dissipation process by quenching chlorophyll singlet excited states in photosynthetic antennae. Additionally, they are also involved in the photoprotection process in green plants as quenchers of chlorophyll triplets and, thus, responsible for protection of the system from the singlet oxygen generation [1]. Artificial light-harvesting antennae are used for better understanding the details of carotenoids involved in light harvesting, energy transfer, electron transfer, and photoprotective processes [1,2]. These artificial structures are capable of performing the specific functions carried out by their natural counterparts. The experimental and theoretical investigation allows one to determine photophysical and photochemical mechanisms underlying the behaviour of the natural systems [2].

Here we present our quantum chemical study of phthalocyanine-carotenoid dyads in which a phenylamino group links phthalocyanine to carotenoids having 8–11 backbone double bonds. We analysed the structures in the ground and excited electronic state, the dependence of electronic excitation characteristics of dyads on the conjugation length of carotenoids. The geometry optimizations were performed using DFT (in the ground electronic state) and TD-DFT (in the excited electronic state) with the CAM-B3LYP long-distance corrected exchange-correlation functional and the 6-31G(d,p) basis set.

Literature [1] R. Berera, C. Herrero, I. H. M. van Stokkum, M. Vengris, G. Kodis, R. E. Palacios, H.

van Amerongen, R. van Grondelle, D. Gust, T. A. Moore, A. L. Moore, J. T. M. Kennis, PNAS 103 (2006) pp. 5343–5348.

[2] M. Kloz, S. Pillai, G. Kodis, D. Gust, T. A. Moore, A. L. Moore, R. van Grondelle, J. T. M. Kennis, J. Am. Chem. Soc. 133 (2011) pp. 7007–7015.

50



Simulation of exciton evolution in a single light-harvesting complex LH2

Tomas Marčiulionis1, Darius Abramavičius1 and Gediminas Trinkūnas2

1 Vilnius university, Vilnius, Lithuania 2 Center for Physical Sciences and Technology, Vilnius, Lithuania

The ways photosynthetic organisms harvest the solar energy and adjust flexibly to environmental extremes have been of considerable long-term interest. At least partly, this steady attention is fuelled by the hope of finding useful biomimetic principles applicable in synthetic molecular devices. Closely packed non-covalently bound pigment molecules constitute the photoactive part of most photosynthetic complexes, while the protein frame affects the electronic properties of the pigments by supplying them with individual binding sites. Recently the nature of electronic excitations created by photon absorption in the cyclic B850 aggregates of 18 bacteriochlorophyll molecules of LH2 antenna complexes of photosynthetic bacteria has been thoroughly studied over a broad temperature range using absorption, fluorescence, fluorescence anisotropy spectra [1] as well as 2D coherent spectroscopy [2]. On the basis of variational approach we were able to develop the consistent self-trapped exciton model very well reproducing all the above steady state spectroscopic data. In the light of emerging data on ultrafast dynamics of single complexes [3] we here present the attempt to extend this model to the time domain. In order to follow the exciton evolution during its lifetime we assume that the protein deformations at pigment sites initiated by the Frenkel exciton are governed by the Langevin equation permanently triggered by the varying local excitations. Preliminary results of model simulations show a very complex exciton behaviour. Particularly, it includes various emissive states the switching between which was reported in [4] as well as their specific fluorescence band shape fluctuations [5]. Literature [1] M. Pajusalu et al. ChemPhysChem 12, 634 (2011). [2] O. Rancova, D. Abramavicius, J. Phys. Chem. B 118 7533 (2014). [3] D. Brinks et al. Chem. Soc. Rev. 43, 2476 (2014). [4] S. Schau-Cohen et al. PNAS 110, 10899 (2013). [5] D. Rutkauskas et al. Biophys. J. 90, 2475 (2006).

51



Multicolour optical vortices formation by radial polarization S-wave plate converter

Mindaugas Gecevičius1,2, Maksym Ivanov4, Titas Gertus3, Aidas Matijošius1 and Valerijus Smilgevičius1

1Vilnius University Laser Research Center, Vilnius, Lithuania 2Optoelectronics Research Centre, University of Southampton, United Kingdom

3UAB „Altechna“, Vilnius, Lithuania 4Taurida National V.I.Vernadsky University, Simferopol, Ukraine

So called, S-waveplate, depending on the polarization of the input beam, allows generation of azimuthally/radially polarized beams or optical vortex beam [1], with generation efficiency of about 99%. It manufactured from widespread material of silica glass and has high damage threshold level. Until the recent time, it was considered that this method is also strongly wave length dependent. In this work we present results of the investigation of possibility to use the S-waveplate for generation of optical vortices in wide spectrum region. By using S-waveplate (manufactured for the certain 530 nm wave length) with different wave lengths, the output beam can easily be cleaned by simply using the quarter-wave plate and linear polarizer placed after S-waveplate. At the output we have perfect optical vortices with zero intensity in the centre at any wavelength and all the noise (Gaussian beam) due to wavelength mismatching is in orthogonally polarized field.

In our experiments we used S-waveplate fabricated by using femtosecond micromachining technology (UAB “Altechna”). The S-waveplate was illuminated by femtosecond light pulses tuned in 350-1090 nm by optical parametric amplifier “Topas” (UAB “Light Conversion”). Experimental results, presented in Fig. 1, demonstrate intensity distributions (see insets) of formed optical vortices and with polarizer filtered noise (Gaussian beam). Fig. 1 shows the distributions of normed power conversion efficiencies vs wave length of the radiation (upper curve represents optical vortex and lower curve corresponds to orthogonally polarized noise radiation).

Literature [1] M. Beresna, M. Gecevičius, P. G. Kazansky, Opt. Mater. Express, 1 (4), 783 (2011)

Fig. 1. Efficiency of vortex-noise conversion vs wave length of the radiation.

52



Performance of alchemical free energy methods in ligand-binding simulations

Paulius Mikulskis1, Samuel Genheden2 and Ulf Ryde1

1 Chemical Center, Department of Theoretical Chemistry, Lund, Sweden 2 Chemistry, University of Southampton, Highfield, SO17 1BJ, Southampton, United Kingdom

The alchemical free energy methods can calculate absolute or relative free energy for the binding of a small molecule to a biological macromolecule. These methods are becoming increasingly affordable owing to the increase in computational power. Calculating free energies could help in the drug development process by reducing the need to perform experiments. For free energy methods to be useful, the accuracy should be similar to that of experiments, viz. around 4 kJ/mol.

We have performed a large-scale test of alchemical perturbation calculations with the Bennett acceptance ratio (BAR) approach to estimate relative affinities for the binding of 107 ligands to 10 different proteins [1]. Using 20 Å truncated spherical systems and one intermediate state, an error of less than 4 kJ/mol was obtained for 54% of the studied relative affinities and a precision of 0.5 kJ/mol on average. Including the whole protein in the calculations and more intermediate states, the results could be improved somewhat, but for three proteins, no satisfactory results could be obtained.

We have also investigated how free energy methods perform on a blind-test challenge (SAMPL4), predicting the binding of nine cyclic carboxylate guest molecules to the octa-acid host. We used four different approaches: Molecular-mechanics (MM), density functional theory (DFT), DFT with optimized coordinates and local coupled-cluster calculations with single and double excitations, and noniterative perturbative treatment of triple excitations (LCCSD(T0)). The MM method gave correlation coefficient of 0.8 compared to the experimental results, but the quantum-mechanical (QM) methods did not improve the results, probably owing to a too large difference between the MM and QM potential-energy functions.

Literature [1] P. Mikulskis, S. Genheden, U. Ryde, A large-scale test of free-energy simulation estimates of protein–ligand binding affinities J. Chem. Inf. Model., 54 (10), 2794–2806 (2014)

[2] P. Mikulskis, D. Cioloboc, M. Andrejic, S. Khare, J. Brorsson, S. Genheden, R. A. Mata, P. Söderhjem, U. Ryde, J. Comput. Aided Mol. Des. 28 (4), 375-400 (2014)

53



White light continuum seeded picosecond OPA

Martynas Miškinis1, Rimantas Grigonis1, 2

1 Light Conversion, Ltd., Lithuania 2 Vilnius University, Faculty of Physics, Department of Quantum Electronics, Vilnius

Lithuania

In this work we present experimental results comparing picosecond optical parametric amplifier (OPA) output parameter dependence on seed signal. Picosecond optical parametric amplifiers are usually seeded with super fluorescence generators. To get better stability of OPA white light continuum (WLC) could be used as a seed for parametric amplification [1].

Optical damage of material is one of the main issues for white light generation using picoseconds laser pulses [2]. We investigated a set of materials for WLC generation. Experimental results showed that YAG crystal is suitable crystals for WLC generation.

As a reference for amplification scheme we took commercially available amplifier TOPAS-800 ps (Light Conversion Ltd.). seeded by super fluorescence generator. TOPAS-800 ps scheme was modified – additional WLC generation stage and seed formation stage was included. The performance, pulse-to-pulse stability, temporal and spectral characteristics of both OPA’s was measured under the same pump parameters. One of the main advantages of using WLC as a seed for optical parametric amplification is improved pulse-to-pulse stability. The comparison of pulse-to-pulse stability is presented in Error! Reference source not found..

Literature [1] G. Cerullo and S. De Silvestri, Ultrafast optical parametric amplifiers, Rev. Sci. Instrum. 74, 1-18 (2003). [2] R.R. Alfano, „The Supercontinuum

Laser Source (Second Edition)“,

Springer Science+Business Media,

2006.

Figure 1. Stability of Signal energy of WLC and super fluorescence seeded OPA

54



Nanofocusing x-ray optics for synchrotrons

Karolis Parfeniukas, Jussi Rahomäki, Fredrik Uhlén, and Ulrich Vogt

KTH Royal Institute of Technology, Biomedical and X-ray Physics, Stockholm, Sweden

X-ray nanoimaging is a high-demand tool as evidenced by demand of such facilities at synchrotron light sources across the globe. A new Swedish facility MAX IV is nearing completion and will open in 2016. NanoMAX is one of the first 7 beamlines to be operational at MAX IV [1]. The purpose of NanoMAX is to perform nanoscale imaging, including other techniques that will benefit from a small focal spot. The aim is to utilize the excellent beam characteristics at the facility to form a sub-10 nm focus.

This work employs Fresnel zone plates because of their ability to achieve small focal spots despite having comparably low efficiency. Zone plate efficiency depends on the thickness of the device material. It is also dependent on the wavelength and therefore one zone plate is typically manufactured for a small range of the spectrum. Tungsten was chosen for this work because of its excellent etching performance and high phase shifting capability at low thicknesses, making it well suited for high energy X-ray applications [2]

One of the main challenges is the thin film synthesis for zone plate fabrication. Tungsten films are very sensitive to the gas pressure during deposition due to imposed internal stress. Small deviations from the equilibrium lead to bending of the substrate, whereas large deviations result in complete changes of internal film structure unsuitable for processing.

The film is then processed by conventional electron beam lithography and reactive ion cryogenic etching using a chromium hard mask to manufacture the final zone plate structure, featuring up to a 200 μm diameter and down to 12 nm smallest feature size [3].

Optimized fabrication methods to produce a zone plate with state of the art performance for high energy X-rays will be described. A proof-of-concept device will be tested at the Diamond Light Souce in December, and the performance analysis will be presented at the conference.

Literature [1] U. Johansson, U. Vogt, and A. Mikkelsen, Proc. SPIE 8851, X-Ray Nanoimaging: Instruments and Methods, 88510L (2013). [2] P. Charalambous, AIP Conf. Proc. 65 (2011). [3] J. Reinspach, F. Uhlen, H. M. Hertz, and A. Holmberg, J. Vac. Sci. Technol. B Microelectron. Nanom. Struct., 29, 06FG02 (2011).

55



Ultrafast relaxation dynamics of excited plasmons in diamond like carbon:Cu and Ag nanocomposite films

Domantas Peckus1,2, Tomas Tamulevičius1, Šarūnas Meškinis1, Asta Tamulevičienė1, Arvydas Čiegis1, Andrius Vasiliauskas1, Orestas Ulčinas1 and Sigitas Tamulevičius1

1Institute of Materials Science of Kaunas University of Technology, K. Baršausko g. 59, Kaunas LT-51423, Lithuania

2Center for Physical Sciences and Technology, Savanorių Ave. 231, Vilnius LT-02300, Lithuania

Recently, the study of electronic and optical properties of metallic nanoparticles became one of the most active areas of nanoscience and technology. This interest is because of many potential applications like energy transfer waveguides, biosensors, imaging and biomedical applications. One of the most active research issues in this field is study of electronic energy relaxation processes of laser excited plasmonic nanoparticles. The excited plasmons in noble metal nanoparticles have several relaxation steps; including electron-phonon, and phonon-phonon interaction with corresponding times of ~1 and ~100 ps [1]. In the current research surface plasmon dynamics of Cu and Ag nanoparticles embedded in a diamond like carbon (DLC) matrix were analyzed [2]. DLC films (100 nm in thickness) with different metal content were synthesized employing unbalanced magnetron sputtering of metal (Cu or Ag) targets with argon ions in acetylene gas atmosphere. The size of nanoparticles and chemical composition of the films were determined employing XRD, TEM, SEM-EDS and AFM. Optical properties were analyzed with UV-VIS-NIR spectrometer, while ultrafast processes - employing transient absorption spectrometer (HARPIA, Light Conversion Ltd.). We investigated the influence of metal content in nanocomposites on relaxation processes of excited (hot) electrons in case of Cu and Ag nanoparticles. The investigations revealed evidential Cu concentration influence on the hot electron relaxation dynamics, while in DLC:Ag nanocomposites dependences were more complicated. The electron-phonon and phonon-phonon relaxation were clearly seen in the DLC:Ag nanocomposites, while in DLC:Cu only electron-phonon relaxation was identified [3]. We cannot neglect phonon-phonon relaxation in DLC:Cu, but its transient absorption signal was comparable with a measurement noise. This research was funded by the European Social Fund under the Global Grant measure (NIRSOLIS Grant No. VP1-3.1-ŠMM-07-K-03-057).

References [1] W. Huand, J. Phys. Chem. C Lett., 111, 10751 (2007). [2] Š. Meškinis, Diam. Relat. Mater. 40, 32 (2013). [3] T. Tamulevičius, Proc. SPIE 9163, 91632J (2014).

56



Temperature-dependent Photoreflectance and Photoluminescence Spectroscopy of InAs Quantum Dots-in-

a-Well Structures

Evelina Pozingytė, Andrius Rimkus, Ramūnas Nedzinskas, Bronislovas Čechavičius, Julius Kavaliauskas, Gintaras Valušis

Center for Physical Sciences and Technology, Vilnius, Lithuania

Self-assembling InAs/GaAs quantum dots (QDs) have been used for optoelectronic devices, such as QD infrared photodetectors (QDIPs). Recently, a new design of QDIPs was proposed, where InAs QDs are embedded within InGaAs/GaAs/AlAs quantum well (QW). This dots-in-a-well (DWELL) quantum heterostructure allows a control of peak wavelength by changing width and composition of the QW, and/or by adding an external electric field. However, better knowledge about optical properties and electronic structure is essential for optimizing the operation of these new design QDIPs.

This work presents a comparative spectroscopic study of DWELL structures grown by molecular beam epitaxy devoting the special interest to an effect of strain-relieving InGaAs layer on InAs QDs. Photoluminescence (PL) and photoreflectance (PR) techniques were used to explore QD- and QW-related optical interband transitions at temperature from 3 to 300 K. Moreover, contactless electroreflectance (CER) measurements at room temperature were performed for comparison.

Temperature-dependent PR and PL spectra of both InGaAs-capped and uncapped DWELL structures revealed a variety of optical transitions within InAs QDs and InGaAs/GaAs/AlAs QWs. Experimental PR results together with numerical calculations suggested that the red-shift of InAs QD ground-state transition is mostly due to a larger dot size and reduced strain within QDs. In addition, PL data allowed to derive electron activation energies and, thereby, provided an insight into thermal quenching processes. Also, a narrower PL linewidth for the InGaAs-capped sample indicated a more homogeneous size distribution of dots. Furthermore, a similar spectra achieved by PR and CER at 300 K implied that electro-modulation of the built-in electric field via quantum-confined Stark effect is a dominant modulation mechanism.

Fig. 1. Temperature-dependent PR and PL spectra of DWELL structure with strain-relieving InGaAs layer.

57



Femtosecond stimulated Raman scattering: theory, apparatus and applications

Kipras Redeckas1, Vladislava Voiciuk1 and Mikas Vengris1

1Laser Research Center, Quantum Electronics Department, Vilnius University, Saulėtekio 10, LT-10223 Vilnius, Lithuania

Time-resolved vibrational spectroscopy is a powerful experimental tool for identifying and characterizing the molecular motions that originate within an electronically-excited system. Femtosecond stimulated Raman scattering (FSRS) [1-3] is a relatively novel, yet promising spectroscopic method which offers both great spectral (∆ν<5 cm-1) and temporal (∆τ<50 fs) resolution, without violating the Heisenberg uncertainty principle [4]. In this work we present a home-built FSRS system, showcase its capabilities, limitations and future prospects, along with its application to a number of model molecular systems (ground state FSRS spectra of several solvents and laser dyes, time resolved FSRS spectra of β-carotene and indolo-benzoxazine type photochromic compound, etc.).

Literature [1] D.W. McCamant, P. Kukura and R.A. Mathies, Applied Spectroscopy 57, 1317–1323 (2003). [2] S.Y Lee, D. Zhang, D.W. McCamant, P. Kukura and R.A. Mathies, The Journal of Chemical Physics 121, 3632–3642 (2004). [3] D.W. McCamant, P. Kukura, S. Yoon and R.A. Mathies, Review of Scientific Instruments 75, 4971–4980 (2004). [4] P. Kukura; D.W. McCamant and R.A. Mathies, Annual Review of Physical Chemistry 58, 461–488 (2007).

58



Wafer-scale leaning Ag and Au nanopillar structures for surface-enhanced Raman scattering applications

Tomas Rindzevicius1, Kaiyu Wu1, Michael Stenbæk Schmidt1, Mikhail Vorobiev2, Jan Barten2 and Anja Boisen1

1 Department of Micro- and Nanotechnology, Technical University of Denmark, DTU Nanotech, DK-2800 Kgs. Lyngby, Denmark

2 Hansa Fine Chemicals GmbH, Bitz, Fahrenheitstr. 1, D-28359 Bremen, Germany Wafer-scale Ag and Au nanopillar (NP) surface-enhanced Raman scattering (SERS) substrates fabricated using maskless lithography are presented. The nanofabrication process can be adopted for high volume manufacturing targets, i.e. involves only four simple process steps: (i) Si reactive ion etching, (ii) O2-plasma treatment, (iii) deposition of Cr adhesion layers, and (iv) evaporation of Ag or Au metal films. The fabricated plasmonic nanostructures exhibit strong electromagnetic field enhancement properties and are excellent SERS substrates suitable for molecular detection. Droplets of analyte can be deposited on the SERS substrate and the molecular fingerprint can be recorded down to nM concentrations. Importantly, solvent drying pulls metal NPs together forming microsized nanopillar clusters. Due to an increased plasmonic coupling between adjacent NPs, high SERS intensities can be observed. We demonstrate that leaning NP structures are suitable for SERS molecular detection at extremely low analyte concentrations, i.e. 100 pM of trans-1,2-bis (4-pyridyl) ethylene (BPE) is recorded showing distinct characteristic Raman vibrational modes. The performance of the Au and Ag NP substrates for specific applications is further evaluated. We target low concentrations (nM) of toxic polychlorinated biphenyls (PCBs) and folic acid (FA) compounds. Detection of PCBs is paramount because it causes a number of harmful effects including cancer [1]. PCBs are still frequently found worldwide in environment [2,3], animal source-food [4] and natural waters [5]. FA is relevant for the development of drug delivery systems and probes for detection of cancer cells over-expressing folate receptors [6].

Literature [1] R. Golden, J. Doull, W. Waddell, and J. Mandel, Crit. Rev. Toxicol. 33, (2003), 543. [2] Y. F. Li, T. Harner, L. Liu, Z. Zhang, N. Q. Ren, H. Jia, J. Ma, and E. Sverko, Environ. Sci. Technol. 44, (2010), 2784. [3] L. A. Rodenburg, J. Guo, S. Du, and G. J. Cavallo, Environ. Sci. Technol. 44, (2010), 2816. [4] F. E. Ahmed, TrAC Trends Anal. Chem. 22, 170 (2003). [5] D. L. Swackhamer and R. A. Hites, Environ. Sci. Technol. 22, (1988), 543. [6] J. J. Castillo, T. Rindzevicius, L. V. Novoa, W. E. Svendsen, N. Rozlosnik, A. Boisen, P. Escobar, F. Martínez, and J. Castillo-León, J. Mater. Chem. B, 2013, 1, 1475.

59



Simulation of electrical properties in femtosecond-laser sulfur

hyperdoped silicon solar cells

Augustinas Ruibys1,*, Thomas Gimpel2, Stefan Kontermann2, and Wolfgang Schade3

1 Affiliated to the Institute of Computer and Network Engineering,

TU Braunschweig, Hans-Sommer-Str. 66, 38106, Braunschweig, Germany2 Fraunhofer Heinrich Hertz Institute, Am Stollen 19B, 38640 Goslar, Germany

3 Clausthal University of Technology, EFZN, Am Stollen 19B, 38640 Goslar, Germany

We use the double diode model to simulate the IV characteristic of a femtosecond laser sulfur

hyperdoped silicon solar cell [1]. We expand this model to include the expected sulfur intermediate

band to account for charge carrier generation by sub band gap illumination [2].

The solar cell suffers a relatively low open circuit voltage. The comparison of both models reveals,

that the solar cell loses the potential energy between the silicon conducting band and the sulfur band

by the directly applied metallic contact, rather than the recombination of charge carriers in the solar

cell itself.

First results of electric properties of indirect contacting of the sulfur band using an amorphous

silicon layer under the metallic contact are presented and commented using the expanded double

diode model.

Literature

[1] S. Kontermann, T. Gimpel, A. L. Baumann, K.-M. Guenther, W. Schade. Laser processed black

silicon for photovoltaic applications. Energy Procedia 27 (2012) 390-395

[2] K.-M. Guenther, T. Gimpel, J. W. Tomm, S. Winter, A. Ruibys, S. Kontermann, W. Schade.

Excess carrier generation in femtosecond-laser processed sulfur doped silicon by means of sub-

bandgap illumination. Appl. Phys. Lett. 104, 042107 (2014)

* Work performed while working at the Fraunhofer Heinrich Hertz Institute, Am Stollen 19B, 38640 Goslar, Germany

60



Alignment of magnetic solenoid lenses for minimizing temporal distorsions of ultrashort electron pulses

Deividas Sabonis1, Daniel Kreier2, Peter Baum2,3

1Faculty of Physics, Technische Universität München, Germany, 2Faculty of Physics, Ludwig-Maximilians-Universität München, Germany.

3Max-Planck-Institut für Quantenoptik, Germany

Always present focusing elements for charged particles are the magnetic solenoid lenses, capable of focusing continuous beams or ultrashort pulses in a similar way. However the perfect alignment of magnetic lens in real experiments is hardly possible. Recently it was noted that misalignment of the lens assembly, i.e. displacement or tilt around axis of symmetry, causes significant temporal aberrations on a femtosecond time scale. This misalignment destroys the symmetry of magnetic lens system and electron pulse, because the central electrons now are being deflected by the magnetic lens instead of propagating unaffected. The pulse lengthening is only minimized if the lens is aligned central and perpendicular to the electron beam. Therefore the purpose of this work is to identify the influence of magnetic lens misalignment effects to the temporal resolution of ultrashort pulses in ultrafast electron diffraction. This question is not easily treated firstly due to the complexity of modern electron optical devices. Therefore discussion goes along with the model case of a simple solenoid lens. A simplified electron source was studied to understand the basic mechanisms of temporal distortions in magnetic lens. To investigate effect of lens on ultrashort pulses it is needed to disregard all other mechanisms for temporal distorsions and assume infinitely short pulses entering the magnetic lens. It is also necessary to disregard any possibility of tilted pulses and restrict discussion to incoming pulses of flat shape. Here an experimental procedure is presented based on periodic reversal of the magnetic field for aligning position and tilt with sufficient precision for reducing the aberrations to less than one femtosecond [1]. The principles used here for a solenoid is intended to be a starting point for more specific studies of realistic lenses in modern electron microscopes and diffraction apparatuses to reach ultimate temporal resolutions, potentially to the attosecond regime of electronic motion.

Literature [1] D. Kreier., D. Sabonis, P. Baum, Alignment of magnetic solenoid lenses for minimizing temporal distortions, J. Opt. 16 075201 (2014).

61



Alignment of magnetic solenoid lenses for minimizing temporal distorsions of ultrashort electron pulses

Deividas Sabonis1, Daniel Kreier2, Peter Baum2,3

1Faculty of Physics, Technische Universität München, Germany, 2Faculty of Physics, Ludwig-Maximilians-Universität München, Germany.

3Max-Planck-Institut für Quantenoptik, Germany

Always present focusing elements for charged particles are the magnetic solenoid lenses, capable of focusing continuous beams or ultrashort pulses in a similar way. However the perfect alignment of magnetic lens in real experiments is hardly possible. Recently it was noted that misalignment of the lens assembly, i.e. displacement or tilt around axis of symmetry, causes significant temporal aberrations on a femtosecond time scale. This misalignment destroys the symmetry of magnetic lens system and electron pulse, because the central electrons now are being deflected by the magnetic lens instead of propagating unaffected. The pulse lengthening is only minimized if the lens is aligned central and perpendicular to the electron beam. Therefore the purpose of this work is to identify the influence of magnetic lens misalignment effects to the temporal resolution of ultrashort pulses in ultrafast electron diffraction. This question is not easily treated firstly due to the complexity of modern electron optical devices. Therefore discussion goes along with the model case of a simple solenoid lens. A simplified electron source was studied to understand the basic mechanisms of temporal distortions in magnetic lens. To investigate effect of lens on ultrashort pulses it is needed to disregard all other mechanisms for temporal distorsions and assume infinitely short pulses entering the magnetic lens. It is also necessary to disregard any possibility of tilted pulses and restrict discussion to incoming pulses of flat shape. Here an experimental procedure is presented based on periodic reversal of the magnetic field for aligning position and tilt with sufficient precision for reducing the aberrations to less than one femtosecond [1]. The principles used here for a solenoid is intended to be a starting point for more specific studies of realistic lenses in modern electron microscopes and diffraction apparatuses to reach ultimate temporal resolutions, potentially to the attosecond regime of electronic motion.

Literature [1] D. Kreier., D. Sabonis, P. Baum, Alignment of magnetic solenoid lenses for minimizing temporal distortions, J. Opt. 16 075201 (2014).

Combined Micro-fabrication Employing Lloyd’s Mirror Interferometer and Direct Laser Writing systems

Linas Šimatonis, Skirmantas Norkus, Tomas Tamulevičius, Dainius Virganavičius, Sigitas Tamulevičius

Institute of Materials Science of Kaunas University of Technology, K. Baršausko st. 59, Kaunas LT-51423, Lithuania

Fabrication of planar integrated optical element with sub-wavelength feature requires advanced lithography techniques, e.g. UV contact, electron beam, nano-imprint lithography, etc. These systems are expensive and bulky. Using one UV laser light source distributed between two optical setups, i.e. Lloyd’s mirror interferometer and Direct Laser Writing (DLW) systems, we were able to pattern micrometer range features together with 100 nm sized lines [1]. Using Lloyd’s mirror holographic lithography system one can fabricate gratings with periods ranging from 200 to 500 nm. In a current setup a solid state laser beam is expanded and filtered with a spatial filter. Half of the laser beam illuminates the sample directly while the second half is reflected from the mirror and interferes with direct beam on the sample surface (Fig. 1). Adjusting the angle of incidence one can control the pitch of the interference fringes. DLW system is based on sample exposure with focused laser beam. The size of the focused spot on the sample surface is less than 5 µm in diameter. The serial exposure of the sample is realized translating it on motorized XY stage (Fig. 1). Automated exposure, selection of the pitch and sample translation are controlled from one software. Patterns are recorded on flat substrates spincoated with negative tone photoresist. Exposed areas of the photoresist film are polymerized and become insoluble after developing in appropriate solution. Employing described optical setup test structures including texts, simple elements of integrated optics and more complex planar structures were realized. Microstructures were analysed employing scanning electron (SEM) and optical microscopes (Fig. 2).

Fig.1. Lloyd’s mirror interferometer and DLW

setup Fig.2. SEM micrograph of fine vertical lines imposed by

interference and horizontal line exposed with DLW Acknowledgments: TT, DV, ST - VP1-3.1-ŠMM-10-V-02-028; SN, TT - LMT student research practice; LŠ, TT, DV, ST - LMT MIP 2013/85.

References[1] D. Virganavičius et. al, Proc. SPIE, 91701 (2014).

62



Supercontinuum generation in solid-state dielectric media

with picosecond laser pulses

Milda Skeivytė1*, Ieva Gražulevičiūtė1, Justinas Galinis1, Gintaras Tamošauskas1, Vytautas Jukna2, Audrius Dubietis1

1Department of Quantum Electronics, Vilnius University, LT-10222 Vilnius, Lithuania 2Centre de Physique Theorique, CNRS, Ecole Polytechnique, F-91128 Palaiseau, France

Supercontinuum (SC) generation in bulk dielectric media is a very efficient method for production of broadband radiation with excellent spatial and temporal coherence properties at various parts of the optical spectrum. During the last decades, SC generation was widely studied in a variety of solid-state media with femtosecond (100 fs and shorter) laser pulses, using amplified Ti:sapphire lasers as predominant pump sources [1]. Recent advances in the development of novel solid-state laser systems, such as based on Yb-doped lasers in particular, see e.g. [2], prompted experimental investigations of SC generation in solid-state dielectric media using picosecond laser pulses. Most of these efforts are directed toward development of ultrabroadband table-top optical parametric chirped pulse amplification (OPCPA)-based systems, where picosecond SC seeding markedly simplifies the overall setup, excluding the need of employing optically synchronized broadband laser oscillator source [3]. In this Contribution we present a detailed numerical and experimental study of SC generation by self-focusing and filamentation of 1.1 ps, 1055 nm laser pulses in YAG crystal. Numerical simulations based on solving the unidirectional nonparaxial propagation equation uncover that spatiotemporal dynamics of self-focusing picosecond pulses is more complex and markedly different from that observed in femtosecond filamentation regime [4]. In particular, we show that free electron plasma plays a dominant role in spatiotemporal reshaping of picosecond laser pulses, producing a Bessel-like spatial intensity distribution at the pulse tail, which thereafter undergoes temporal splitting and produces an octave-spanning supercontinuum, covering wavelength range from 460 nm to 1.8 m, in excellent agreement with experimental data. Moreover, our measurements demonstrate that SC is generated without the onset of optical damage. Its spectral shape is highly reproducible from pulse-to-pulse, with a standard deviation of spectral intensity fluctuations less than 3% throughout the major part of the SC spectrum. This research was funded by the European Social Fund under the Global Grant measure, grant No. VP1-3.1-SMM-07-K-03-001. References

1. M. Bradler, P. Baum, E. Riedle, Appl. Phys. B 97, 561 (2009). 2. A. Vaupel, N. Bodner, B. Webb, L. Shah, M. Richardson, Opt. Eng. 53, 051507 (2014). 3. R. Riedel, A. Stephanides, M. J. Prandolini, B. Gronloh, B. Jungbluth, T. Mans, F. Tavella, Opt.

Lett. 39, 1422 (2014). 4. V. Jukna, J. Galinis, G. Tamošauskas, D. Majus, A. Dubietis, Appl. Phys. B 116, 477 (2014).

63



Gold nanoclusters for X-ray and fluorescence bioimaging

Akvilė Šlėktaitė1,2, Laura Kačenauskaitė2, ir Ričardas Rotomskis1,3

1 Nacionalinis vėžio institutas, Biomedicininės fizikos laboratorija, Vilnius, Lithuania 2 Vilniaus universitetas, Gamtos mokslų fakultetas, Vilnius, Lithuania

3 Vilniaus universitetas, Fizikos fakultetas, Vilnius, Lithuania

Fluorescent imaging is one of the main methods in bioimaging, however it is still not fully adapted in medical practice. Main drawbacks are limited examination depth in living tissue and imperfect characteristics of exogenous fluorescent agents. Meanwhile, the key method in medical diagnostics is X-ray imaging. This method is based on distinct X-ray contrast of different biological tissue, but often needs an additional contrast enhancement by exogenous contrast media. Currently used iodine-based contrast agents can lead to toxic effects in kidneys, also have short blood circulation half-life and cannot be functionalized for selective targeting.

Here we propose dual modality agents – fluorescent gold nanoclusters (AuNCs), which could be suitable for both X-Ray and fluorescent imaging. These imaging probes could overcome discussed drawbacks and bring optical methods closer to everyday medicine. Fluorescent AuNCs show great promise in bioimaging due to their extremely small size (less than 2 nm), which do not influence any biological functions of the live units. They present high fluorescence yield, are biocompatible and can be functionalized for further selectivity. Also due to the high atomic number of gold, AuNCs provide much higher X-ray contrast intensity than iodine based agents.

In this work we studied fluorescence and X-ray imaging possibilities of MES capped AuNCs. Synthesis of nanoclusters was performed using modified method suggested by Bao et al. under different acidity levels and temperature from 37°C to 90°C to reach the most efficient fluorescence yield. We found that fluorescence intensity of AuNCs could be increased up to 100 times with suitable pH and temperature choice. Subsequently particles were concentrated and their X-ray contrast was observed using standard mammographic unit at 20 kVp energy and 50 mAs exposition. In conclusion, MES capped gold nanoparticles are capable of both fluorescence and X-ray contrastivity, therefore could be used as multimodal contrast agent in bioimaging.

References

Y. Bao et al., Formation and Stabilization of Fluorescent Gold nanoclusters Using Small Molecules, J. Phys. Chem., 114(38), 15879-15882 (2010).

64



Improvement of temporal coherence of down-converted waves in optical parametric amplifier with incoherent pump

Paulius Stanislovaitis and Viktorija Pyragaitė

Department of Quantum Electronics, Faculty of Physics, Vilnius University, Saulėtekio ave. 9, Building 3, LT-10222, Vilnius, Lithuania

In this work we study parametric amplification process, when pump and signal waves are both incoherent and signal and idler have group velocities of different sign with respect to pump. Second order dispersion is neglected. We show in numerical experiments, that during such interaction, narrowing of the signal spectrum is obtained. Thus, improvement of signal coherence is expected at the output.

This work was supported by Research Council of Lithuania, project No. MIP-073/2013.

Fig. 1. Normalized average signal spectra (100 iterations) : signal spectrum at the input (1), in the middle of the crystal (2) and at the output (3). The crystal length of 10 mm was taken, while the nonlinear length has been selected to be 2 mm.

Literature [1] A. Picozzi and P. Aschieri. Influence of dispersion on the resonant interaction between three incoherent waves, Phys. Rev. E 72, 046606 (2005)

65



Formation of optical vortices with topological charge |l| = 2

using the radial polarization converter

Paulius Stanislovaitis, Valerijus Smilgevičius and Aidas Matijošius

Department of Quantum Electronics, Faculty of Physics, Vilnius University, Saulėtekioave. 9, Building 3, LT-10222, Vilnius, Lithuania

It is a well-known fact that the radial polarization converter (RPC) can be used to produce

optical vortices of unit topological charge from circularly polarized light [1,2]. In this work we

show a new technique that allows to generate an optical vortex of double topological charge,

using only a single RPC. Operation of RPC on circularly polarized optical vortices is described

theoretically and an experimental technique for double-charged optical vortex generation is

proposed. The resulting beam is analyzed using the Michelson interferometer.

(a) (b)

Fig. 1. Intensity distribution of optical vortex with topological charge |l|=2, obtained from

experiment (a) and interference pattern, obtained with Michelson interferometer (b). In the

interference pattern, splitting of one fringe into three is seen, indicating presence of an optical

vortex with topological charge |l|=2.

Literature

[1] M. Beresna, M. Gecevičius, P. G. Kazansky, T. Gertus. Radially polarized optical

vortex converter created by femtosecond nanostructuring of glass, Appl. Phys. Lett. 98,

201101 (2011)

[2] A. Matijošius, P. Stanislovaitis, T. Gertus, V. Smilgevičius. Formation of optical

vortices with topological charge |l|=1 and |l|=1/2 by use of the S-waveplate, Opt.

Commun. 324 1-9 (2014)

66



Influence of Silver Nanoparticles on Optical Properties of Organic Dyes

Simona Streckaitė1, Domantas Peckus1,2, Ramūnas Augulis1, Tomas Tamulevičius2, Sigitas Tamulevičius2 and Vidmantas Gulbinas1

1 Institute of Physics, Center for Physical Sciences and Technology, A. Goštauto g. 11, Vilnius LT-01108, Lithuania

2 Institute of Materials Science of Kaunas University of Technology, K. Baršausko g. 59, Kaunas LT-51423, Lithuania

Recently, silver nanoparticles have attracted much attention because of their unique size and shape dependent optical [1], electrical and magnetic properties. Possible manipulations of these properties lead to various applications of silver nanoparticles in optoelectronics, biosensing, catalysis, enhanced optical spectroscopies [2], as antimicrobials [3] and other [4]. For practical use it is crucial to understand the influence of size, shape, aggregation, stability [5] and other features of nanoparticles to their optical properties. In this work, influence of spherical silver nanoparticles on optical properties of highly fluorescent organic dyes (rhodamine 6G (R6G), sulforhodamine 640 (SR640)) was investigated. Silver nanoparticles were prepared using wet-chemistry technique from reduction of silver salt (AgNO3 + NaBH4 → Ag + H2 + B2H6 + NaNO3). Solutions of nanoparticles and organic dies were investigated by using steady-state and ultrafast time-resolved absorption and fluorescence spectroscopy. Steady-state absorption spectra showed that R6G causes aggregation in Ag nanoparticle solution because Cl- ion, which disrupts the borohydride (B2H6) protective layer around nanoparticles. On the contrary, SR640 stabilizes the Ag nanoparticle solution. Analysis of ultrafast time-resolved spectroscopy measurements revealed influence of localized surface plasmon resonance of Ag nanoparticles to R6G and SR640 exited state relaxation dynamics.

Literature [1] A. V. Sorokin, A. A. Zabolotskii, N. V. Pereverzev, S. L. Yefimova, Y. V. Malyukin, and A. I. Plekhanov, J. Phys. Chem. C 118, 7599−7605 (2014). [2] J. R. G. Navarro and M. H. V Werts, Analyst 138, 583-592 (2013). [3] S. Agnihotri, S. Mukherji, and S. Mukherji, RSC Adv. 4, 3974-3983 (2014). [4] M. U. Rashid, M. K. H. Bhuiyan, and M. E. Quayum, Dhaka Univ. J. Pharm. Sci. 12, 29-33 (2013). [5] M. Franckevičius, A. Gustainytė, R. Kondrotas, R. Juškėnas, M. Marcos, J. L. Serrano, R. Vaišnoras, and V. Gulbinas, J. Nanoparticle Res. 16, 2343 (2014).

67



ENERGY TRANSFER OF AN EM FIELD SCATTERED BY A FINITE COMPOSITE SET OF CYLINDERS

Giedrius Tušinskis1

1 Department of Theoretical Physics, Vilnius University, Lithuania

Here we investigate the transfer of energy of plane EM waves through an array of parallel cylinders placed in a row. The row of cylinders is made such to be separated into three sets of cylinders 2 sets of cylinders made from metal and a set of dielectric cylinders made from silicon, which has the permittivity 𝜀𝜀𝑆𝑆𝑆𝑆 = 11.8 − 𝑆𝑆

𝜌𝜌𝜌𝜌𝜌𝜌0 in between the sets of metal

cylinders. We investigate the transfer of energy with different angles of rotation of the set in respect to the direction of the propagation of the wave. The direction of propagation of the wave is parallel to Χ axis and the straight line connecting the centers of the cylinders is at different angles with the X axis. Calculating techniques allow us to solve boundary problems of complex two-dimensional structures made from cylinders [1]. Fig. 1a Fig. 1b

Fig. 1. Radial part of Poynting vector ( 𝑊𝑊𝑚𝑚2), when the propagation of the wave is parallel to the row of the cylinders

(a) and when the set is rotated by 𝜋𝜋3 (b) the frequency of the incident plane wave, f=12GHz. Here we present the radial part of Poynting vector of a scattered plane EM wave with different rotations of the array of 9 cylinders with resistivity of 𝜌𝜌 = 10Ω𝑚𝑚. The distance between the centers of the cylinders is 4.2mm and the radius of the cylinders is R=2mm.

Literature [1] A. K. Ozturk and R. Paknys Analysis of Propagation Between Rows of Conducting Cylinders That Model Solid Surfaces Using the Same Surface Area Rule. IEEE Transactions on Antennas Propagation, VOL. 60, NO. 5, 2602-2606, (2012).

68



A study of the fluctuating initial states for relativistic hydrodynamics applied for the heavy ion collisions at LHC

energies Monika Venčkauskaitė, Karolis Tamošiūnas

Teorinės fizikos ir astronomijos institutas, A. Goštauto g. 12, 01108 Vilnius, Lithuania

Similar conditions to those of the very early universe, can be created in particle accelerators during heavy ion collisions. During these collisions hundreds of protons and neutrons smash into one another at energies of up to a few teraelectronvolts. Inside this system the quark gluon plasma (QGP) can be created.

QGP due to its nature cannot be detected in the particle accelerators directly. However, it is possible to study its properties from particle distributions, which are created after the hadronization.

We examine the initial conditions of heavy ion collisions at LHC (2760 GeV) and RHIC (200 GeV) energies and use them to describe the hydrodynamical evolution of the system and compare calculated particle multiplicity distributions and elliptic flow rapidity dependence with experimental data.

It will be shown, that using Glauber Monte Carlo model as an initial state (fig 1, fig 2) for the hydrodynamic evolution based on the approximate Landau solution we obtain particle multiplicity distribution and elliptic flow parameter distribution. Moreover, obtained results are in good agreement with the experimental data from LHC and RHIC colliders for a different impact parameters and at different collision energies.

Literature [1] K. Tamošiūnas, Eur. Phys. J. A (2011) 47: 121

Fig. 2: Energy density distribution of peripheral lead ion collision (impact parameter 7.5 - 8 fm).

Fig. 1: Energy density distribution of central lead ion collision (impact parameter 0 - 0.5 fm).

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Redefining the established understanding of excitation dynamics of photochromic oxazines

Vladislava Voiciuk1, Kipras Redeckas1, Vytas Martinaitis2, Rasa Steponavičiūtė2, Algirdas Šačkus2, Mikas Vengris1

1 Department of Quantum Electronics, Vilnius University, Vilnius, Lithuania 2 Institute of Synthetic Chemistry, Kaunas University of Technology, Kaunas, Lithuania

Since the introduction of the photochromic indole-benzoxazines [1, 2], induced absorption bands in their transient spectra have been assigned to the ground state absorption of ring-opened isomer. This assignment relies on the postulated resemblance of photo- and chemically induced spectra. For the first time, we bring forward the issue of discrepancy between the absorption spectra of photoproducts and corresponding chemically opened forms. As a result, a substantial change in the current explanation of photodynamics of photochromic oxazines was proposed. Triplet state nature of the photoproduct was hypothesized and tested in acetonitrile by measuring the effect of oxygen quenching of the excited states. It was shown that the induced absorption of photochromic oxazines in acetonitrile is triplet state absorption, and the ring opening does not occur. Thus, in acetonitrile solutions, photochromic oxazines should no longer be considered as molecular switches. On the other hand, in methanol solutions the formation of the ring-opened form is favored.

Literature [1] M. Tomasulo, S. Sortino, and F.M. Raymo, Organic Letters 7, 1109 (2005). [2] M. Tomasulo, et al., Journal of Organic Chemistry 70, 8180 (2005).

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