cavity enhanced spectroscopy 2017 - radboud universiteitclaire vallance (1m1) applications of...

Cavity Enhanced Spectroscopy 2017

12th International User Meeting & Summer School

12 - 15 June 2017 in Hotel Zuiderduin in Egmond aan Zee, The Netherlands.

Sponsors


12th International User Meeting & Summer School

Organized by:

Radboud University

Frans J.M. Harren and Simona M. Cristescu

Trace Gas Research Group

Molecular and Laser Physics

Institute for Molecules and Materials

Secretary: Magda Speijers/Paula Willems


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3

Huygens Building, Science Faculty of the Radboud University in Nijmegen.

Contents

Program Summer School on Cavity Enhanced Spectroscopy 2017 07

Monday 12 June

Abstracts Summer School presentations 08

Program User Meeting on Cavity Enhanced Spectroscopy 2017 12

Tuesday 13 June – Wednesday 14 June and Thursday 15 June

Abstracts Invited & Oral presentations 16

Abstracts Poster presentations 50

Sponsors


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The 12th International User Meeting and Summer School on Cavity Enhanced Spectroscopy will

take place from 12 - 15 June 2017 in Hotel Zuiderduin in Egmond aan Zee, the Netherlands.

LOCATION Conference Center, Hotel Zuiderduin, Egmond aan Zee

the Netherlands

CONFERENCE CHAIR

Frans Harren Radboud University, Nijmegen, the Netherlands

LOCAL ORGANIZING COMMITTEE

Frans Harren Radboud University, Nijmegen, the Netherlands

Simona Cristescu Radboud University, Nijmegen, the Netherlands

Paula Willems Radboud University, Nijmegen, the Netherlands

Magda Speijers Radboud University, Nijmegen, the Netherlands

INTERNATIONAL ADVISORY COMMITTEE

Andy Ruth University College Cork, Cork, Ireland

Jong Chow Australian National University, Canberra, Australia

Gianluca Gagliardi Istituto Nazionale di Ottica (INO), CNR, Napoli, Italy

Peter Loock Queen's University Kingston, Ontario, Canada

Hans Osthoff University of Calgary Calgary, Alberta, Canada

The 12th international User Meeting and Summer School CES 2017 will provide a stimulating

scientific program with lectures, oral and poster presentations.


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INVITED SPEAKERS

Claire Vallance (1M1) Applications of open-access optical microcavities

University of Oxford, Oxford, England

Randall Goldsmith (1M2) Single molecular/particle detection using microresonator cavities

University of Wisconsin, Madison, Wisconsin, USA

Barak Dayan (1M5) Cavity Ring-Up Spectroscopy

Weizmann Instute of Science, Rehovot, Israel

David Hunger (1A10) Cavity enhanced Raman microscopy of individual carbon nanotubes

University of Munich, Munich, Germany

Daniel Lisak (2M1) Cavity-enhanced absorption and dispersion spectroscopy in the frequency domain

Nicholas Copernicus University, Torun, Poland

Gianluca Galzerano (3M1) Direct frequency comb spectroscopy: down to the comb tooth frequency resolution

Polytechnic University of Milan, Milano, Italy

Peter Rakitzis (3M6) Cavity Ring-Down polarimetry

University of Crete, Iraklion, Greece

1M1= day 1, morning, talk 1

1A2= day 1, afternoon, talk 2

SUMMER SCHOOL LECTURERS – Monday 12 June 2017

Kevin K. Lehmann University of Virginia, Charlottesville, Virginia, USA

Claire Vallance University of Oxford, Oxford, England

Harold Linnartz Leiden Observatory, Leiden, the Netherlands

Julien Mandon Radboud University, Nijmegen, the Netherlands

Rebecca Washenfelder NOAA Chemical Sciences Division, Boulder, Colorado, USA


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Lehmann Presentation Award and EPS Poster Prize

Lehmann Presentation Award

The conference awards the “Lehmann Presentation Award” (sponsored by Tiger Optics) of 500 Euro

for an early career researcher (PhD student, young postdoc), in recognition of the most excellent oral

presentation at the conference.

EPS Poster Prize

The EPS encourages recognition of the scientific merit of early career researchers. Grants are

available to EPS Europhysics and EPS Sponsored Conferences for poster prize for researchers in the

PhD phase of his/her career in recognition of an excellent poster at the conference. The amount of

each prize grant is 200 Euro.


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Monday 12 June Summer School on Cavity Enhanced Spectroscopy 2017

Program

08:30 Welcome Summer School and registration

09:00 Frans Harren, Radboud University, Nijmegen, the Netherlands Opening

09:15 Kevin K. Lehmann, University of Virginia, Charlottesville VA, USA Sensitivity Limits of Cavity Enhanced Spectroscopies 10:30 Coffee break 11:00 Claire Vallance, University of Oxford, Oxford, UK Taking the plunge: cavity-enhanced spectroscopy in solution 12:30 Lunch 14:00 Harold V.J. Linnartz, Leiden University, Leiden, the Netherlands

How to use cavity enhanced spectroscopy in astrochemistry? 15:00 Julien Mandon, Radboud University, Nijmegen, the Netherlands

Integrated Cavity Output Spectroscopy and Trace Gas Sensing in Life-Science 16:00 Coffee & Tea break 16:30 Rebecca A. Washenfelder, University of Colorado, Boulder, Colorado, USA

Atmospheric Field Measurements Using Cavity Enhanced Spectroscopy

19:30 Dinner


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Abstracts

Summer School presentations


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9.15-10.15 Sensitivity Limits of Cavity Enhanced Spectroscopies

Kevin K. Lehmann

Departments of Chemistry and Physics, Univ. of Virginia, Charlottesville VA, USA

In this talk, I will review theoretical sensitivity limits for several versions of Cavity Enhanced Spectroscopies, including how these are derived. Important practical methods to improve sensitivity will be discussed. The sensitivities realized in experiments will be presented.

11.00-12.00 Taking the plunge: cavity-enhanced spectroscopy in solution

Claire Vallance

Department of Chemistry, University of Oxford

Cavity-enhanced spectroscopies were originally developed for the sensitive detection of gas-phase molecules, and have been supremely successful in applications ranging from fundamental spectroscopy through atmospheric chemistry to breath analysis for medical diagnostics. There has been considerably less interest in applying cavity-enhanced methods to the liquid or solution phase, though many of the benefits found in the gas phase still apply. The lower take up for solution-phase applications is partly because the much higher molecular densities mean that the very high detection sensitivities offered by cavity enhanced methods are less critical, but also partly because of the many challenges associated with performing such measurements in solution. These include scattering by the solvent, mirror contamination, reflectivity changes, and losses associated with introducing sample containers into the cavity. In this tutorial lecture we will (i) investigate some of the different approaches that have been used to perform cavity-enhanced spectroscopic measurements on liquid phase samples; (ii) consider the effect of the solution and/or a sample container on the mirror reflectivity and cavity Q factor; and (iii) analyse a data set from a liquid-phase assay in order both to identify potential pitfalls and to consider potential approaches for improving detection sensitivity.

14.00-15.00 How to use cavity enhanced spectroscopy in astrochemistry?

Harold V.J. Linnartz

Chair for Laboratory Astrophysics, Leiden Observatory

Leiden University, the Netherlands,

The broader context of this lecture is 'astrochemistry', i.e., the chemical processes taking place under the harsh conditions in inter- and circumstellar space. The focus is on cavity enhanced technology. As a group we are going to try to solve a number of rather practical and elementary issues when working with cavity ring down or cavity enhanced spectroscopic techniques.

We will design, step-by-step, a research approach suited to record the molecular fingerprints of molecules present in diffuse and dark interstellar clouds. Some basic spectroscopy is part of the lecture and a small syllabus with reprints with selected papers will be provided.


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15.00-16.00 Integrated Cavity Output Spectroscopy and Trace Gas Sensing in Life-Science

Julien Mandon

Molecular and Laser Physics, Radboud University, Nijmegen, the Netherlands

Trace gas detection systems are used in environmental sciences, biology, agriculture and medical sciences. They often combine a light source, a high finesse cavity and a highly sensitive detector. Here, the performance of different light sources, such as Optical Parametric Oscillators and Quantum cascade lasers is demonstrated in combination with ICOS (Integrated Cavity Output Spectroscopy) for trace gas sensing. Several topics are going to be discussed such as the analysis of exhaled-breath for medical applications.

16.30-17.30 Atmospheric Field Measurements using Cavity Enhanced Spectroscopy

Rebecca A. Washenfelder1,2

1University of Colorado, Boulder, Colorado, USA

2National Oceanic and Atmospheric Administration, Boulder, Colorado, USA

Understanding the chemistry and radiative properties of Earth’s atmosphere requires field measurements of trace gases and aerosol particles. The key trace gases are present at small concentrations, ranging from parts per trillion (pptv; approximately 2 x 107 molecules cm-3) to parts per million (ppmv; approximately 2 x 1013 molecules cm-3), and their detection requires sensitive analytical techniques. During the past two decades, cavity ringdown spectroscopy and other cavity enhanced spectroscopy techniques have provided important new measurements of trace gas concentrations and aerosol optical extinction. I will give an overview of atmospheric field instruments and the scientific problems they are being used to address.


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User Meeting on Cavity Enhanced

Spectroscopy 2017

presentations and posters


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Tuesday 13 June User Meeting on Cavity Enhanced Spectroscopy 2017

Program 1M1= day 1, morning, talk 1


08:15 Welcome and registration

08.45 Frans Harren, Radboud University, Nijmegen, the Netherlands Opening

09:00 Claire Vallance 1M1 (invited), Department of Chemistry, University of Oxford

Chemical sensing with optical microcavities

09:30 Randall H. Goldsmith 1M2 (invited), University of Wisconsin, Madison, USA

Optical Microresonators as Platforms for Single-Molecule Spectroscopy

10:00 Hans-Peter Loock 1M3 (oral presentation), Queen’s University, Kingston, ON, Canada

Silicon microring resonators as platforms for ultracompact chemical sensors

10:15 Dean James 1M4 (oral presentation), University of Oxford, CRL, Oxford, UK

Open-access optical microcavities for small volume liquid analysis

10:30 Coffee break

11:00 Barak Dayan 1M5 (invited), Weizmann Institute of Science, Rehovot, Israel

Cavity Ring-Up Spectroscopy

11:30 Michele Gianella 1M6 (oral presentation), University of Oxford, Oxford, UK

Intra-cavity Faraday modulation spectroscopy

11:45 David A. Long 1M7 (oral presentation), Nat. Inst. of Standards and Technology,

Gaithersburg, Maryland USA

Optical detection of radiocarbon dioxide using mid-infrared cavity ring-down spectroscopy

12:00 Davide Mazzotti 1M8 (oral presentation), INO - CNR, Sesto Fiorentino FI, Italy

Radiocarbon measurements with mid-infrared SCAR spectroscopy

12:15 Luo Han 1M9 (oral presentation), University of Science and Technology of China, Hefei,

Anhui, China

Frequency stabilization of QCL for CO2 isotope abundance analysis with cavity enhancement

absorption spectroscopy

12:30 Lunch

14:00 David Hunger 1A10 (invited), Karlsruhe Institute of Technology, Karlsruhe, Germany

Cavity-Enhanced Raman Microscopy

14:30 Jean-Pierre H. van Helden 1A11 (oral presentation), INP, Greifswald, Germany

Detection of HO2 in an atmospheric pressure plasma jet using optical feedback cavity-

enhanced absorption spectroscopy


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14:45 Charles R. Markus 1A12 (oral presentation), University of Illinois, Urbana, IL, US

Cavity enhanced spectroscopy of molecular ions in the mid-infrared with up-conversion

detection and Brewster-plate spoilers

15:00 Tilo M. Zollitsch 1A13 (oral presentation), University of Oxford, Oxford, UK

Using cavity ring down spectroscopy to investigate magnetically sensitive radical

photochemistry of de novo and natural flavoproteins

15:15 Gianluca Gagliardi 1A14 (oral presentation), Istituto Nazionale di Ottica, Pozzuoli (Naples),

Italy

Investigation of opto-mechanical effects in high-Q liquid droplet microresonators

15:30 Coffee & Tea break

16.00 Photo CES2017

16:15 Poster session until 18:00 hours

19:30 Dinner

Wednesday 14 June User Meeting on Cavity Enhanced Spectroscopy 2017

09:00 Daniel Lisak 2M1 (invited), Nicolaus Copernicus University, Torun, Poland

Cavity-enhanced absorption and dispersion spectroscopy in the frequency domain

09:30 Alexandra C. Johansson 2M2 (oral presentation), Umea University, 901 87 Umea, Sweden

Line parameter retrieval beyond the Voigt profile using comb-based Fourier transform

spectroscopy

09:45 Katarzyna Bielska 2M3 (oral presentation), Nicolaus Copernicus University, Torun, Poland

Dual-beam frequency-stabilized cavity ring-down spectrometer for precise measurements of

spectral line shapes

10:00 Lucile Richard 2M4 (oral presentation), Université Grenoble Alpes / CNRS, Grenoble, France

Optical Feedback - Cavity Enhanced Absorption Spectroscopy with an Interband Cascade

Laser at 4 µm: SO2 trace detection and water vapor continuum measurements

10:15 Amir Khodabakhsh 2M5 (oral presentation), Umeå University, Umeå, Sweden

Mid-infrared cavity-enhanced continuous-filtering Vernier spectroscopy using a femtosecond

optical parametric oscillator

10:30 Coffee break

11:00 Jens H. Wallberg 2M6 (oral presentation), University of Copenhagen, Copenhagen, Denmark

Determination of the oscillator strengths for the third and fourth vibrational overtone

transitions in simple alcohols


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11:15 Szymon Wójtewicz 2M7 (oral presentation) Nicolaus Copernicus University, Torun, Poland

Response of optical cavity to amplitude switching, phase shifting and frequency detuning of

incident light

11:30 Faisal Nadeem 2M8 (oral presentation), Radboud University, Nijmegen, the Netherlands

3- Mirror Off-Axis Integrated Cavity Output Spectroscopy at Near- and Mid-Infrared

Wavelengths

11:45 Patrick Dupré 2M9 (oral presentation), ULCO, Dunkerque, France

Saturated Absorption Modeling in Gas Phase: Dealing with Gaussian Beams

12:00 Antoine Müller 2M10 (sponsor presentation), Alpes Lasers, Blaise, Switzerland, to be announced

12:15 Sören Paulke and Dr. Frank Wunderlich 2M11 (sponsor presentation), Layertec GmbH,

Mellingen, Germany

High performance mirrors for CRD-application made by LAYERTEC

12:30 Marten Beels and Lisa Berson 2M12 (sponsor presentation), Tiger Optics, Warrington, PA, USA

Spectroscopic Solutions for Research Institutes

12:45 Lunch

14.00 excursion by bus: Zaanse Schans

18:30 back at the Hotel Zuiderduin

20:00 start Conference dinner in beach restaurant De Schelp


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Thursday 15 June User Meeting on Cavity Enhanced Spectroscopy 2017

09:00 T. Peter Rakitzis 3M1 (invited), University of Crete, 71003 Heraklion-Crete, Greece

Cavity Ring-Down polarimetry

09:30 Lucile Rutkowski 3M2 (oral presentation), Umeå University, 901 87 Umeå, Sweden

Direct broadband measurement of cavity modes using a mechanical Fourier transform

spectrometer with kHz resolution

09:45 Marco Marangoni 3M3 (oral presentation), CNR, Milano, Italy A Cavity-Ring-Down Doppler-Broadening Thermometer

10:00 Hua Xia 3M4 (oral presentation), Chinese Academy of Sciences, Hefei, Anhui, China

Single-QCL-based cavity enhancement absorption spectroscopy for simultaneous detection of

CO2 and 13C, 18O isotopes 10:15 Coffee break 10:45 Gianluca Galzerano 3M5 (invited), CNR, Milano, Italy

Direct frequency comb spectroscopy: down to the comb tooth frequency resolution 11:15 Juho Karhu 3M6 (oral presentation), University of Helsinki, Helsinki, Finland

Two-photon sub-Doppler ro-vibrational spectroscopy using cavity ring-down detection

11:30 Xavier Bacalla 3M7 (oral presentation), VUA, Amsterdam, the Netherlands

Spectroscopic survey of electronic transitions of C6H, 13C6H, and C6D using CRDS

11:45 Thomas Hausmaninger 3M8 (oral presentation), Umeå University, 901 87 Umeå, Sweden

Depletion of the lowest vibrational state of CH4 in absorption spectroscopy at 3.3 µm in N2

and air in the 1 to 100 Torr range

12:00-12.15 Award session and Closing Remarks

12:30-14:00 Lunch


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Abstracts

Invited & Oral presentations

1M1= day 1, morning, talk 1



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09:00-09:30 1M1 (invited)

Chemical sensing with optical microcavities

Claire Vallance1 , Dean James1, Aurelien Trichet2, and Jason Smith2

1Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Rd, Oxford OX1 3TA, UK

2Department of Materials, University of Oxford, 16 Parks Rd, Oxford OX1 3PH, UK

Cavity-enhanced spectroscopies are widely used for highly sensitive spectroscopic absorption measurements in the gas phase. However, they also show considerable promise as a method for enhancing detection sensitivity in measurements on small liquid volumes, such as those encountered in "lab on a chip" and chemical sensing applications. Optical microcavities [1] offer a general platform to enable sensitive measurement of refractive index changes and optical absorption by tracking perturbations to the frequency and intensity of individual cavity modes as fluids are flowed through the cavity. The cavity modes can also be used to trap single nanoparticles and probe their properties. The very small probed volumes coupled with the sensitivity enhancement offered by the cavity allow us to detect fewer than 100 molecules via their optical absorption, with planned improvements offering the tantalising possibility of achieving single-molecule detection in the future.

Figure: Finite difference time domain (FDTD) simulation of the electric field for light trapped within a cavity mode of an optical microcavity.

Acknowledgments: This work has the support of the Leverhulme Trust, the Royal Society’s Paul Instrument Fund, and the EPSRC.

References [1] C. Vallance, A. P. Trichet, D. James, P. R. Dolan, and J. M. Smith, ‘Open access microcavities for chemical sensing’, Nanotechnology 27, 274003 (2016).


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09:30-10:30 1M2 (invited)

Optical Microresonators as Platforms for Single-Molecule Spectroscopy

Randall H. Goldsmith1

1Univeristy of Wisconsin, Madison, USA

Single-particle spectroscopy is a powerful tool for the investigation of the properties of

nanomaterials because unsynchronized processes can be directly observed. However, the traditional

reliance upon photoluminescence for single-particle measurements limits such investigations to

systems where the target particle or molecule is emissive.

Ultrahigh-Q optical microresonators offer a way of eliminating the need for emission by

enabling additional sensitive means of interaction with individual particles. We present a new two-

beam experimental geometry[1], where the goal is not detection of individual molecules, but the

measurement of optical spectra and spectral dynamics of non-fluorescent molecules of interest. Our

experiment relies on ultrahigh-Q toroidal optical microresonators as platforms for photothermal

spectroscopy. Transitions are optically driven in the particle or molecule of interest, while the

thermalization of the excitation energy is detected by the resonator.

We will present two examples of applications of our new spectroscopy platform. First, we

will show spectroscopy of individual gold nanoparticles that show strong interactions between the

plasmonic resonance of the nanoparticle and the whispering gallery mode of the optical

microresonator, resulting in substantial changes to the lineshape that are well-captured by theory.

Second, we will show our method can be applied to non-emissive conductive polymer molecules to

probe crystallinity and electronic structure at the single polymer level.

Acknowledgments: This work has the support the National Science Foundation and DARPA.

References

[1] K. D. Heylman, N. Thakkar, E. H. Horak, C. Cherqui, S. C. Quillin, K. A. Knapper, D. J. Masiello, R. H.

Goldsmith, “Optical microresonators as single-particle absorption spectrometers.” Nature

Photonics,10, 788-795, 2016.


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10:00-10:15 1M3 (oral presentation)

Silicon microring resonators as platforms for ultracompact chemical sensors

Hao Chen, Sogol Borjian, Xiaowei We, John Saunders and Hans-Peter Loock1

Danxia Xu, 2 and Georg Müller 3

1 Dept. of Chemistry, Queen’s University, Kingston, ON, Canada 2National Research Council, Ottawa, ON, Canada

3ABB, Baden, Switzerland

Light propagating through silicon nanowires with dimensions below the wavelength of the light

interacts strongly with the surrounding medium through its evanescent wave. Ring-resonators

fabricated from such silicon-on-insulator (SOI) waveguides are therefore a popular platform for

refractive index sensing with a sensitivity of the resonance frequency of about 100 nm/RIU. In their

most basic form these sensors are quite unspecific and have a high cross-sensitivity to temperature

and strain.

Here we present sensors for heavy metals, and for inorganic ions. The sensors are based on SOI

waveguide ring resonators coated with different mesoporous silica films containing functional groups

that exhibit a high affinity for lead, Pb(II), mercury, Hg(II), and phosphate (PO43-, HPO4

2-). Using these

coatings we observe a large refractive index change upon adsorption of heavy metals and phosphate

from aqueous solution and were able to quantify ppb-level concentrations of heavy metal ions in

water. A second resonator along the same bus waveguide is buried under an impenetrable silica

coating and serves as a reference to allow for temperature drift compensation.

Figure1: (Left) SOI micro-ring resonators. The larger of the two resonators is exposed to the

environment and the smaller one is covered by silica (Right) spectrum of these two microring

resonators.

Acknowledgments: We acknowledge financial and in-kind support by ABB, the National Research

Council and the Natural Science and Engineering Research Council of Canada.


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Open-access optical microcavities for small volume liquid analysis

Dean James1,2, Aurélien Trichet2, Christopher Mason1, Jason Smith2, and Claire Vallance1

1Dept. of Chemistry, University of Oxford, CRL, Mansfield Road, Oxford, OX1 3TA, UK. 2Dept. of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK.

Open-access optical microcavities provide a novel platform for performing label-free spectroscopic

measurements within a microfluidic environment. Arrays of concave micromirrors are fabricated by

focused ion beam milling of a suitable substrate followed by deposition of a suitable dielectric mirror

coating. The mirrors are used to form microcavity arrays by positioning a micromirror array a few

microns from an opposing planar dielectric mirror. The resulting cavities have mode volumes of a few

femtolitres, with cavity finesse on the order of 103 to 104. The small cavity lengths result in a large

free spectral range, such that only one or a few wavelengths are resonant inside the cavity within the

reflection bandwidth of the mirrors. This property is key to the use of the cavities in chemical sensing

applications. The mirror separation can be controlled with sub-nanometre precision using

piezoelectric actuators, providing a simple mechanism for tuning the cavity resonances to any

desired wavelength.

The microcavity arrays have been incorporated into a flow cell, allowing liquid samples to be flowed

into and out of the cavities. In initial proof-of-concept experiments using a broadband halogen light

source we have demonstrated both refractive index and absorption sensing down to the level of a

few thousand molecules. In more recent work utilising higher finesse microcavities and a more

intense and stable light source we have achieved an absorption detection limit of 14 molecules of

methylene blue (a dye used in biological stains). Recent results from these studies will be presented.

(a)

(b)

(c)

Figure: (a) Microscope image of micromirror array; (b) Schematic of open-access plano-concave

microcavity; (c) Single longitudinal mode of microcavity with pathlength 1.5 µm (the shaded regions

indicate the wavelength regions outside the reflectivity bandwidth of the cavity mirrors).

Acknowledgments: This work was funded by the Leverhulme Trust, and the Engineering and Physical

Sciences Research Council (EPSRC).

References

[1] A.A.P. Trichet, et al., Lab on a Chip, 14, 21, 4244-4249 (2014).

[2] C. Vallance, et al., Nanotechnology, 27, 27, 274003 (2016).


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11:00-11:30 1M5 (invited)

Cavity Ring-Up Spectroscopy

Barak Dayan1

1AMOS and Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel.

Cavity Ring-Up Spectroscopy (CRUS) is a coherent scheme for capturing a complete 'snapshot' of the spectrum of a cavity, at the shortest possible (i.e. Fourier-transform limited) timescale - the cavity lifetime. It is in a sense a coherent measurement of the cavity ring-down signal, providing not only the cavity's spectral shape (or lifetime), but also the instantaneous centre frequency.

CRUS is especially applicable to whispering-gallery mode resonators, in which it occurs 'automatically' just by measuring the rising-edge (instead of the falling-edge in cavity ring-down spectroscopy) of detuned pulses.

Spectroscopy of whispering-gallery mode microresonators has become a powerful scientific tool in recent years, enabling the detection of single viruses, nanoparticles and even single molecules. Yet the demonstrated timescale of these schemes has been limited so far to milliseconds or more, as most experiments relied on laser-scanning, which is inherently slow.

CRUS is orders of magnitude faster, capable of capturing complete spectral snapshots at nanosecond timescales. It combines the sensitivity of heterodyne measurements with the highest-possible, transform-limited acquisition rate. As a demonstration, we captured spectra of microtoroid resonators at time intervals as short as 16 ns, directly monitoring sub-microsecond dynamics of their optomechanical vibrations, thermorefractive response and Kerr nonlinearity.

CRUS holds promise for the study of fast biological processes such as enzyme kinetics, protein folding and light harvesting, with applications in other fields such as cavity quantum electrodynamics and pulsed optomechanics.

Ref: Nature Communications 6, 6788 (2015)


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Intra-cavity Faraday modulation spectroscopy (INFAMOS)

Michele Gianella, Tomas Pinto and Grant A.D. Ritchie1

1Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South

Parks Road, Oxford OX1 3QZ, United Kingdom

Intra-cavity Faraday modulation spectroscopy (INFAMOS) is a sensitive and selective spectroscopic

technique that exploits the Faraday effect in paramagnetic (radical) species. By confining the sample

inside a high finesse optical cavity, the Faraday rotation angle is increased by several orders of

magnitude[1].

Figure 1 shows our INFAMOS spectrometer for the detection of nitric oxide at 5.2 m. It is based on

an OF-CEAS spectrometer with a linear cavity [2] to which an AC magnetic field is applied

longitudinally by a solenoid. In figure 2, the Faraday rotation signal measured around the 3/2R(3.5)

transition of NO is shown. The limit of detection is 0.5 ppbv/Hz1/2, comparable with non-cavity based

state-of-the-art systems that operate close to the shot-noise limit [3].

Ample room for improvement in this novel technique make it promising for the detection of various

other radicals as well (e.g. HO2 in the atmosphere).

Figure 1: INFAMOS spectrometer for the detection of NO.

Figure 2: Faraday rotation signal of the

3/2R(3.5) transition at 1890.9 cm-1 with a

NO concentration of 0.2 ppmv.

Acknowledgments: This work is funded by the National Environmental Research Council (NERC)

(NE/M016439/1) and through an Organisation Research Excellence Grant (IND63-REG2) from the

European Metrology Research Programme (EMRP).

References

[1] D. Jacob et al., Applied Physics Letters 66, 3546 (1995).

[2] K.M. Manfred, L. Ciaffoni and G.A.D Ritchie, Applied Physics B 120, 329 (2015).

[3] E. Zhang et al., Sensors 15, 25992 (2015).


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Optical detection of radiocarbon dioxide using mid-infrared cavity ring-down spectroscopy

D. A. Long,1 A. J. Fleisher,1 Q. Liu,1 and J. T. Hodges1

1Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau

Drive, Gaithersburg, Maryland USA

Radiocarbon (14C) is a long lived radioactive isotope of carbon which is commonly used in

radiocarbon dating to determine the age of a wide variety of materials. In addition, measurements of

radiocarbon can determine if a compound was produced via biological or petrochemical means as

fossil fuels and their byproducts are depleted in 14C. Measurements of 14C are however quite difficult

due to its low naturally occurring abundance with expensive techniques such as accelerator mass

spectrometry commonly employed.

An alternate approach for these challenging measurements is through the use of cavity-enhanced

spectroscopy in the mid-infrared spectral region. I will describe our development of a mid-infrared

cavity ring-down spectrometer and its application for measurements of radiocarbon dioxide at and

below ambient levels. Ongoing system improvements will also be addressed in an effort to increase

our sensitivity and stability. Finally, I will touch upon future measurement targets and application

areas.

Figure 1: Averaged histogram for repeated sets of measurements taken across several days. Each

measurement was comprised of forty individual scans requiring 75 minutes of acquisition time.


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Radiocarbon measurements with mid-infrared SCAR spectroscopy

Iacopo Galli1,2,3, Saverio Bartalini1,2,3, Marco Barucci1, Pablo Cancio1,2,3, Giovanni Giusfredi1,2,3, Davide

Mazzotti1,2,3, Naota Akikusa4, Licia Romano7, Franco D'agostino7, Maria Elena Fedi5, Pier Andrea

Mandò5,6, Paolo De Natale1,2,3

1Istituto Nazionale di Ottica (INO) - CNR, Via Carrara 1, 50019 Sesto Fiorentino FI, Italy

2European Laboratory for Nonlinear Spectroscopy (LENS), Via Carrara 1, 50019 Sesto Fiorentino FI, Italy

3ppqSense S.r.l., Via Gattinella 20, 50013 Campi Bisenzio FI, Italy

4Development Bureau Laser Device R&D Group, Hamamatsu Photonics KK, Shizuoka 434-8601, Japan

5Istituto Nazionale di Fisica Nucleare (INFN) - Sez. Firenze, Via Sansone 1, 50019 Sesto Fiorentino FI, Italy

6Dipartimento di Fisica e Astronomia, Università di Firenze, Via Sansone 1, 50019 Sesto Fiorentino FI, Italy

7Dipartimento Istituto Italiano di Studi Orientali, Sapienza Università di Roma, P.le Moro 5, 00185 Roma, Italy

Since its first invention and demonstration [1], saturated-absorption cavity ring-down spectroscopy

(SCAR) of CO2 gas samples at 4.5 µm wavelength has been approaching accelerator mass

spectrometry (AMS) precision in radiocarbon measurements. The first intercomparison between

SCAR and AMS measurements was performed with modern (from fermentation of brown cane sugar)

and fossil (from high-purity industrial gas cylinder) carbon dioxide samples [2]. These successful

results have triggered further optimization of the data fitting procedure [3] and significant upgrades

of the SCAR experimental apparatus, leading to an improved performance of the spectrometer in

terms of precision and repeatability [4]. A theoretical error analysis has also provided predictions of

the ultimate sensitivity limits that can be realized with this detection method [5]. Finally, an

independent research group has recently reproduced SCAR spectroscopy, assessing the working

limits of this technique in terms of saturation parameter with measurements on a different

molecular species [6].

We will present, for the first time, radiocarbon measurements performed with our SCAR

spectrometer on samples of archaeological interest from the Abu Tbeirah site in the Southern Iraq.

We believe that, being the SCAR apparatus much more transportable than any AMS machine, the

presented results pave the way to radiocarbon dating on archaeological sites. Moreover, the

exploitation of the SCAR technique for in situ measurements can be extended to different application

fields, such as environment, nuclear security, pharmacology.

References

[1] Galli et al., Phys. Rev. Lett. 107, 270802 (2011); R. N. Zare, Nature 482, 312 (2012).

Radiocarbon 55, 213 (2013).

[3] Giusfredi et al., J. Opt. Soc. Am. B 32, 2223 (2015).

Optica 3, 385 (2016).

[5] K. K. Lehmann, Appl. Phys. B 116, 147 (2014).

Phys. Chem. Chem. Phys. 18, 22978 (2016).


25


Frequency stabilization of QCL for CO2 isotope abundance analysis with cavity enhancement absorption spectroscopy

L. Han1,2, F.Z.Dong1,2,H. Xia2, Z.R.Zhang2, T. Pang2, P.S.Sun2, S.Liu2 and X.J.Cui2 1School of Environment Science and Optoelectronic Technology, University of Science and Technology

of China, Hefei, Anhui 230026, China 2Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine

Mechanics, Chinese Academy of Sciences, Hefei, Anhui 230031, China

The spectral range of 4.32μm is convenient to measure the carbon and oxygen isotope abundance of

CO2 gas. We use QCL laser to scan the absorption spectrum and get the concentration of this three

kind gas 16O12C16O、16O13C16O、16O12C18O. Thus, the isotopic abundance of 13C and 18O of CO2 gas can

be detected in real time. Isotopic abundance is significant for the study of climate and ecology.

However, the laser wavelength is affected by the external environment temperature in the process

of using QCL laser. We develop a method to control the wavelength of QCL. By comparing the signal

we get with the standard signal, the wavelength shift is obtained, the driving current is changed, and

the wavelength position is corrected. We tested the background signal using this method and the

wavelength stabilization level can be controlled at 0.028nm. Finally, the effect of external

environment temperature on the wavelength drift of QCL laser is eliminated and the stability of the

system is improved.[1]

16O12C16O16O12C18O

16O13C16O

Start

Filtering And Denoising

Compared with standard signal

Retrieving Gas Concentration

Isotope abundance

Adjusting By Serial

Regulating DC current

Changing the wavelength

DriftNo drift

Figure: The absorption spectrum of16O12C16O、16O13C16O、16O12C18O(left) and Control flow

chart(right)

Acknowledgments: Thanks to the National Natural Science Foundation of China (41405034) and the

Special Fund for Basic Research on Scientific Instruments of the Chinese Academy of Sciences

(YZ201315).

References

[1] R. Wehr, J. W. Munger, D. D. Nelson, J. B. McManus, M. S. Zahniser, S. C. Wofsy, and S.R. Saleska,

Measuring forest-atmosphere exchange of 13C16O2, 18O12C16O, and 12C16O2 by eddy covariance, Agric.

For. Meteorol. 181, 69–84 (2013) .


26

14:00-14:30 1A10 (invited)

Cavity-Enhanced Raman Microscopy

David Hunger1, Thomas Hümmer2,3, Matthias Mader2,3, Jonathan Noe2,4, Matthias S. Hofmann2,4, Theodor W. Hänsch2,3 , Alexander Högele2,4

1Karlsruhe Institute of Technology, Wolfgang-Gaede-Str. 1, Karlsruhe, Germany 2Ludwig-Maximilians-University, Schellingstr. 4, 80799 Munich, Germany

3Max-Planck-Institute of Quantum Optics, Hans Kopfermann-Str. 1, 85748 Garching, Germany 4Center for Nanoscience, Ludwig-Maximilians-University, Schellingstr. 4, 80799 Munich,

Germany Raman spectroscopy reveals chemically specific information and provides label-free insight into the molecular world. However, the signals are intrinsically weak and call for enhancement techniques. In this talk, we present Purcell enhancement of Raman scattering in a tunable high-finesse microcavity [1], and discuss its use it for molecular diagnostics by combined Raman and absorption imaging [2,3]. Studying individual single-wall carbon nanotubes (CNTs), we identify crucial structural parameters such as nanotube radius, electronic structure and extinction cross section. We observe a 320-times enhanced Raman scattering spectral density and an effective Purcell factor of 6.2, together with a collection efficiency of 60% [3]. Potential for significantly higher enhancement, quantitative signals, inherent spectral filtering and absence of intrinsic background in cavity-vacuum stimulated Raman scattering render the technique a promising tool for molecular imaging.

Figure: Left: Sketch of the Experiment – a laser-machined and mirror-coated fiber tip together with a planar mirror that carries the sample (CNTs) forms a scanning microcavity. Middle: Cavity-enhanced Raman image showing the strength of the G-Band of single-walled CNTs. Right: Comparison of the G-Band spectrum recorded with a confocal microscope (blue) and with the cavity tuned to the G-Band maximum (red).

References [1] D. Hunger et al., New J. Phys. 12, 065038 (2010). [2] M. Mader et al., Nat. Commun. 6, 7249 (2015). [3] T. Hümmer et al., Nat. Commun. 7, 12155 (2016).


27

14:30-14:45 1A11 (oral presentation)

Detection of HO2 in an atmospheric pressure plasma jet using optical feedback cavity-

enhanced absorption spectroscopy

Michele Gianella1, Stephan Reuter2, Ana Lawry Aguila1, N. Lang2, J. Röpcke2, Grant A.D. Ritchie1 and

Jean-Pierre H. van Helden2

1Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Rd, Oxford OX1 3QZ, UK

2Leibniz Institute for Plasma Science and Technology (INP Greifswald), Felix-Hausdorff-Str. 2, 17489 Greifswald, Germany

Cold non-equilibrium atmospheric pressure plasma jets gain more and more interest as their

technological applications increase in diverse fields such as material processing and plasma medicine

[1]. Hence, it is essential to diagnose the fluxes of the species generated by these plasma sources to

identify relevant fundamental processes and to be able to tailor the produced species for specific

applications. Due to their small size (in µm to cm range) and high density gradients in space and time,

these jets, however, are difficult to diagnose quantitatively. Absorption spectroscopy has become a

popular method for characterizing the fluxes of species generated by these plasma sources [2].

However, the small geometry of the effluent of a plasma jet severely limits the sensitivity of

absorption spectroscopy, especially for highly reactive transient species. To overcome the difficulty

of small absorption lengths, cavity-enhanced spectroscopy is a promising method for localized

measurements of species with relatively low abundances in plasma jets. In this contribution, we

report on the detection of the highly reactive hydroperoxyl radical, HO2, in the effluent of a cold

argon plasma jet, which is applied in plasma medicine, by the use of optical feedback cavity-

enhanced absorption spectroscopy (OF-CEAS) [3]. In this way, effective absorption path lengths of up

to 100 meters in a mm-sized plasma jet could be achieved. The HO2 concentration for different feed

gas humidity as well as for different gas curtain mixtures of oxygen and nitrogen around the plasma

jet was investigated. The achieved detection levels indicate that such a spectrometer will find broad

application in future studies of the chemical network in the effluents of plasma jets and provides a

new way of testing and improving our modelling of these complex plasma environments.

Acknowledgments: This work was funded by: Leibniz Competition 2015 (SAW-2015-INP-5); Ministry

of Education, Science and Culture of the State of Mecklenburg-Vorpommern (AU15001); European

Union Seventh Framework Programme FP7/2007-2013 (316216); Natural Environment Research

Council (NERC) (NE/M016439/1).

References

[1] T. von Woedtke, S. Reuter, K. Masur, and K.-D. Weltmann, Phys. Rep. 530, 291 (2013).

[2] S. Reuter, J.S. Sousa, G.D. Stancu, and J.H. van Helden, Plasma Sources Sci. Technol. 24, 054001

(2015)

[3] M. Gianella, S. Reuter, A. Lawry Aguila, G.A.D. Ritchie, and J.H. van Helden, New J. Phys. 18,

113027 (2016).


28


Cavity enhanced spectroscopy of molecular ions in the mid-infrared with up-conversion

detection and Brewster-plate spoilers

Charles R. Markus1, Jefferson E. McCollum1, Thomas S. Dieter2, Phillip A. Kocheril1, and Benjamin J.

McCall,1,2,3

1Deparment of Chemistry, University of Illinois, Urbana, IL 2Department of Physics, University of Illinois, Urbana, IL

3Department of Astronomy, University of Illinois, Urbana, IL

Precise and accurate measurements of rovibrational transition frequencies of molecular ions are

valuable to molecular theorists and astrochemists. Our method Noise-Immune Cavity-Enhanced

Optical Heterodyne Velocity Modulation Spectroscopy (NICE-OHVMS) combines the sensitivity of

Noise-Immune Cavity-Enhanced Optical Heterodyne Molecular Spectroscopy (NICE-OHMS) with the

ion-neutral discrimination of Velocity Modulation Spectroscopy.[1] Our instrument consists of an

optical parametric oscillator (OPO; 3.2 – 4.6 µm) and a low finesse cavity which contains a liquid

nitrogen cooled positive column discharge cell. When the frequency is referenced to an optical

frequency comb, measurements of the sub-Doppler features which arise due to the high intracavity

power (10 – 12 W) enable precise and accurate determination of rest frequencies. With NICE-

OHVMS, we have measured a number of transitions of H3+, HeH+, and OH+ with the highest precision

to date.[2,3,4]

However, like many sensitive mid-infrared techniques, NICE-OHVMS was limited by

background signals from parasitic etalons and by the performance of mid-infrared detectors. We

have eliminated etalon fringes using a dithered optic known as a Brewster-plate spoiler[5] without

strongly interfering with our laser-to-cavity lock. We have also improved our detection scheme by

up-converting the light transmitted from our cavity with difference frequency generation (DFG) to

enable the use of fast and sensitive silicon based detectors. With these two improvements, we have

reached a noise equivalent absorption of 6 x 10-11 cm-1 Hz-1/2, a factor of 34 improvement over the

previous implementation of NICE-OHVMS.[6] With the improved sensitivity, we have investigated

transitions of H3+ that were previously too weak to measure with NICE-OHVMS, which have been

used to calculate experimentally determined energy level spacings in the ground vibrational state.

These improvements will enable us to continue our survey of H3+ and to pursue new targets which

were previously undetectable.

References

[1] K.N. Crabtree et al. Chem. Phys. Lett. (2011), 551, 1-6.

[2] J.N. Hodges et al. J. Chem. Phys. (2013), 139, 164201.

[3] A.J. Perry et al. J. Chem. Phys. (2014), 141, 101101.

[4] C.R. Markus et al. Astrophys. J. (2016), 817, 138.

[5] C.R. Webster J. Opt. Soc. Am. B (1985), 2, 1464-1470.

[6] C.R. Markus et al. Opt. Express (2017), 25, 3709-3721.


29


Using cavity ring down spectroscopy to investigate magnetically sensitive radical

photochemistry of de novo and natural flavoproteins

Tilo M. Zollitsch,1 Lauren E. Jarocha,1 C. Bialas,2 Kevin B. Henbest,1 P. Leslie Dutton,2 Christopher C. Moser,2 Christiane R. Timmel,1 Peter J. Hore,1 and Stuart R. Mackenzie1

1Department of Chemistry, University of Oxford, Oxford, United Kingdom 2Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, U.S.A

Magnetic field effects (MFE) on the photochemistry of de novo and natural flavoproteins have been investigated by cavity ring-down spectroscopy (CRDS). The simple, robust, and adaptable design of the de novo flavoproteins (flavomaquettes) facilitates MFE studies by circumventing the complexity and diversity of their natural counterparts (cryptochromes) which are believed to play an important role in animal magnetoreception. We have recently demonstrated that photoinduced electron transfer occurs in these flavomaquettes leading to the formation of a spin-correlated radical pair which exhibits MFEs at room temperature.1 In this work, the profound effect of the donor-acceptor distance on the MFE is demonstrated using flavomaquettes with distinctive flavin-tryptophan distances.2 CRDS was used to detect MFEs with sub-µs time resolution and a sensitivity two orders of magnitude greater than conventional single pass transient absorption techniques. The innovative approach applying cavity enhanced spectroscopy to both natural cryptochromes and purposefully designed artificial flavoproteins opens up new pathways to explore MFEs in biologically relevant environments. Figure: A) Flavomaquettes with tryptophan at increasing distance to the flavin chromophore.

B) Percentage MFE as a function of magnetic field strength of various maquette designs.

Acknowledgments: European Research Council, Grant Agreement No. 340451 Air Force Office of Scientific Research, USAF Award No. FA9550-14-1-0095

References [1] Bialas, C.; Jarocha, L. E.; Henbest, K. B.; Zollitsch, T. M.; Kodali, G.; Timmel, C. R.; Mackenzie, S. R.; Dutton, P. L.; Moser, C. C.; Hore, P. J., J. Am. Chem. Soc. 2016, 138 (51), 16584-16587. [2] Zollitsch, T. M.; Jarocha, L. E.; Bialas, C.; Henbest, K. B.; Kodali, G.; Dutton, P. L.; Moser, C. C.; Timmel, C. R.; Hore, P. J.; Mackenzie, S. R.; (in preparation)


30


Investigation of opto-mechanical effects in high-Q liquid droplet microresonators

A. Giorgini1, S. Avino1, P. Malara1, P. De Natale2 and Gianluca Gagliardi1

1Consiglio Nazionale delle Ricerche, Istituto Nazionale di Ottica (INO), via Campi Flegrei, 34 -

Comprensorio A. Olivetti, 80078 Pozzuoli (Naples), Italy

2Consiglio Nazionale delle Ricerche, Istituto Nazionale di Ottica (INO),

Largo E. Fermi 6, 50125 Firenze, Italy

Optical whispering-gallery modes (WGMs) have extensively been investigated in solid micro-cavities

of various geometries and materials demonstrating impressive quality (Q) factors, even higher than

109 [1]. The peculiarity of WGMs supported by such solid structures is that they can be excited via

evanescent-wave coupling and resonant light travels along closed paths at the interface between the

surface of the resonator and the surrounding environment. Unfortunately, most of the light

circulates inside the resonator and only a very small fraction is used for light-matter interaction,

thereby reducing its effective enhancement in applications. Here, we use cavities made directly from

liquid droplets as micro-resonators. The droplet itself serves as the cavity and the sample at the same

time, exploiting the internal optical field to probe dissolved analytes or particles [2]. We perform

free-space excitation and demonstrate laser-frequency locking on whispering-gallery modes coupled

in vertically-suspended droplets [3,4]. The intrinsic Q-factor limit of oil droplets is investigated by

means of cavity photon lifetime measurements, observing values up to 107, in the visible spectral

region [5]. Based on very recent experimental results, we will show that these microresonators also

exhibit interesting non-linear properties that potentially allow for the excitation of surface waves and

very fast vibrations in the liquid medium. Imaging and spectroscopic investigation of these effects

will be presented.

Acknowledgments: This work has the support of Italian Ministry of Education and Research with the

project PON “Monica” and Campania Region with the project POR “Bersagli”.

References

[1] K. J. Vahala, Nature 424 , 839 (2003)

[2] M. R. Foreman, S. Avino, R. Zullo, H.-P. Loock, F. Vollmer, and G. Gagliardi, Eur. Phys. J. Special

Topics 223, 1971-1988 (2014)

[3] S. Avino, A. Krause, R. Zullo, A. Giorgini, P. Malara, P. De Natale, H.-P. Loock, and G. Gagliardi, Adv.

Opt. Mat. 2, 1155–1159 (2014)

[4] R. Zullo, A. Giorgini, S. Avino, P. Malara, P. De Natale, and G. Gagliardi, Opt. Lett., 41, 650-652

(2016).

[5] A. Giorgini, S. Avino, P. Malara, P. De Natale & G. Gagliardi, “Fundamental limits in high-Q droplet

microresonators”, Sci. Reports, 7, 41997 (2017).


31

09:00-09:30 2M1 (invited)

Cavity-enhanced absorption and dispersion spectroscopy in the frequency domain

Daniel Lisak

Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in

Toruń, Grudziadzka 5, 87-100 Torun, Poland

The exponential light decays measured in the cavity ring-down spectroscopy (CRDS), in the time

domain, are equivalent to the spectral widths of the cavity modes, measured in the frequency

domain. This phenomenon is exploited in the cavity mode-width spectroscopy (CMWS) [1–3] in

which absorption spectrum can be retrieved by precise measurements of half-widths of the cavity

modes. Properties of CRDS and CMWS methods make them complementary in terms of achievable

accuracies at different levels of intra-cavity absorption. For low absorptions, where the ring-down

decays are long and mode widths are small, the best precision is expected with the CRDS. In the

opposite case of high absorption the precision of CMWS should be higher.

Measurement of dispersion mode shifts provides another interesting approach for very accurate

quantitative spectroscopy. Since frequency can be measured most accurately of all physical

quantities, direct measurement of absolute or differential mode frequencies to obtain a spectrum in

the one-dimensional cavity mode dispersion spectroscopy (1D-CMDS) [4,5] should eliminate

potential problems with nonlinearities of detection system and minimize systematic instrumental

errors. Contrary to any absorption spectroscopy, in 1D-CMDS both axes of the spectrum can be

linked to the primary frequency standard [6]. Results of line-shape and line position investigations,

using methods mentioned above, will be presented. These new cavity-enhanced techniques may be

especially useful in applications that require high accuracy of weak absorption measurements, e.g.

gas spectroscopy for atmospheric monitoring and gas metrology, Doppler thermometry, as well as

fundamental study of spectral line shapes. Direct comparison of spectra obtained with various cavity-

enhanced techniques enables identification of potential instrumental errors at sub-percent level of

accuracy.

CMWS and 1D-CMDS methods can be also combined with direct optical frequency comb

spectroscopy with a single-tooth resolved Fourier-transform detection scheme [7]. In this case a

frequency-based broadband absorption and dispersion spectrum can be measured with a kHz-level

resolution.

References

[1] K. Nakagawa, T. Katsuda, A.S. Shelkovnikov, et al., Opt. Commun. 107, 369 (1994)

[2] A. Cygan, D. Lisak, P. Morzyński, et al., Opt. Express 21, 29744 (2013)

[3] D.A. Long, G.-W. Truong, R.D. van Zee, et al., Appl. Phys. B 114, 489 (2014)

[4] A. Cygan, P. Wcisło, S. Wójtewicz, et al., Opt. Express 23, 14472 (2015)

[5] A. Cygan, S. Wójtewicz, M. Zaborowski, et al., Meas. Sci. Technol. 27, 045501 (2016)

[6] A. Cygan, S. Wójtewicz, G. Kowzan, et al., J. Chem. Phys. 144, 214202 (2016).

[7] P. Masłowski, K. F. Lee, A. C. Johansson, et al., Phys. Rev. A 93, 021802 (2016).


32


Line parameter retrieval beyond the Voigt profile using comb-based Fourier transform

spectroscopy

Alexandra C. Johansson1, Lucile Rutkowski1, Piotr Masłowski2, Anna Filipsson1, Amir Khodabakhsh1,

and Aleksandra Foltynowicz1

1 Department of Physics, Umeå University, 901 87 Umeå, Sweden 2 Institute of Physics, Nicolaus Copernicus University, ul. Grudziądzka 5, 87-100 Toruń, Poland

We recently developed a method of optical frequency comb Fourier transform spectroscopy (FTS)

with sub-nominal resolution, in which the individual comb line intensities are measured by matching

the nominal resolution of the FTS to the comb repetition rate [1, 2]. It enables detection of

broadband high-resolution molecular spectra without the influence of the instrumental lineshape

function and with frequency scale given by the comb. Here we present broadband precision

measurements of the 3ν1+ν3 absorption band of CO2 using a system based on an Er:fiber frequency

comb, a high-finesse cavity and an FTS with sub-nominal resolution. Figure (a) shows the spectrum of

the entire band of CO2 in N2 at 26.3 Torr (black) spanning 90 cm-1 measured in 10 min, together with

a model based on the Voigt profile and HITRAN line parameters (red). The high signal-to-noise ratio

allows observing higher order corrections to the lineshape. Figure (b) shows the R16e line at 6359.97

cm-1 (black) with a fit of the Voigt profile (VP, blue) and speed-dependent Voigt profile (SDVP, red),

and the corresponding residuals demonstrating significant improvement for the SDVP fit. The comb-

based FTS with sub-nominal resolution is thus a perfect tool for spectroscopy of entire absorption

bands with precision beyond the Voigt profile and for retrieval of molecular line parameters for

improved spectroscopic databases. Our ongoing work focuses on retrieval of spectral line parameters

of pure CO2 using multiline fitting with the Hartmann-Tran profile.

Figure: (a) Cavity-enhanced spectrum of the 3ν1+ν3 band of 1000 ppm of CO2 in N2 at 26.3 Torr (black) together with a model (red). (b) The R16e line (black markers) along with fits of the VP (blue) and SDVP (red), and the corresponding residuals in the lower panels.

Acknowledgments: This work has the support of Swedish Research Council (621-2012-3650 and

2016-03593), Swedish Foundation for Strategic Research (ICA12-0031), and the Knut and Alice

Wallenberg Foundation (KAW 2015.0159).

References

[1] P. Masłowski, et al., Phys. Rev. A 93, 021802 (2016)

[2]L. Rutkowski, et al., arXiv:1612.04808 [physics.ins-det] (2016)


33


Dual-beam frequency-stabilized cavity ring-down spectrometer for precise measurements

of spectral line shapes

Katarzyna Bielska1, Szymon Wójtewicz1, Jolanta Domysławska1, Robab Hashemi2, Piotr Morzyński1,

Piotr Wcisło1, Michał Słowiński1, Agata Cygan1, Adriana Predoi-Cross3, Roman Ciuryło1, and Daniel

Lisak1

1Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Torun, ul. Grudziadzka 5, 87-100 Torun, Poland

2Department of Physics and Astronomy, University of Lethbridge, 4401 University Drive, T1K3M4 Lethbridge, AB, Canada

3 512 Silkstne Cres. W, Lethbridge AB T1J 4C1 Canada

Oxygen molecule is of great importance for atmospheric research, monitoring of vegetation on the

Earth and investigation of exoplanets atmospheres. Until recently mainly the oxygen A-band at 762

nm was used. Other bands were less frequently used mainly due to lack of accurate enough

reference data and low line intensities. However, there is growing number of applications and

projects which intent to use the O2 B-band at 689 nm.

We present a re-designed CRDS system, which is used for measurements of oxygen B-band lines. The

optical frequency comb assisted, Pound-Drever-Hall locked, frequency-stabilized cavity ring-down

spectrometer (PDH-locked FS-CRDS), previously described in [1] and references therein, has been

significantly modified. The probe laser beam has been split into two parts: one is used as locking

beam, and the other as a probe beam [2]. This enables the application of a locking scheme in which

the probe beam is continuously PDH-locked to the cavity resonance during acquisition of ring down

decays. Together with the use of a more stable optical frequency reference for cavity length

stabilization, we obtain spectra with a signal-to-noise ratio increased by factor of about 3 compared

to the previous spectrometer’s design. The frequency axis is linked to the primary frequency

standard with 10-12 stability [2].

Measurements of oxygen B-band lines perturbed by nitrogen will be presented as an example of

spectrometer operation, together with a detailed line-shape analysis including such effects as Dicke

narrowing, the speed-dependence of collisional broadening and shifting and dispersion asymmetry.

Acknowledgments: This work has the support of National Science Center, Poland project numbers

2014/15/D/ST2/05281, 2015/18/E/ST2/00585, DEC-2013/11/D/ST2/02663 and of the COST Action,

CM1405 MOLIM. R. Hashemi has been supported by the NSERC and Alberta-Innovates Tech Futures,

Canada.

References

[1] J. Domysławska, S. Wójtewicz, P. Masłowski, A. Cygan, K. Bielska, R. S. Trawiński, R. Ciuryło, and D.

Lisak, J. Quant. Spectrosc. Radiat. Transf. 169, 111-121 (2016).

[2] A. Cygan, S. Wójtewicz, G. Kowzan, M. Zaborowski, P. Wcisło, J. Nawrocki, P. Krehlik,

Ł. Śliwczyński, M. Lipiński, P. Masłowski, R. Ciuryło, and D. Lisak, J. Chem. Phys. 144, 214202 (2016)


34


Optical Feedback - Cavity Enhanced Absorption Spectroscopy with an Interband Cascade

Laser at 4 µm: SO2 trace detection and water vapor continuum measurements

Lucile Richard1 and Irène Ventrillard1, Daniele Romanini1, Alain Campargue1, Didier Mondelain1, Kevin

Jaulin2

1LIPhy, Université Grenoble Alpes / CNRS, Grenoble, France 2AP2E S.A.S., Aix en Provence, France

The implementation of Optical Feedback - Cavity Enhanced Absorption Spectroscopy (OF-CEAS) [1,2]

with an Interband Cascade Laser (ICL) offers new perspectives in trace detection. ICLs working close

to room temperature presently cover a rather large spectral region partly overlapping that of

Quantum Cascade Lasers (QCL), however they present electrical characteristics close to those of near

infrared DFB diode lasers. Compared to QCL, ICL requires threshold current 20 to 50 times lower, as

well as 5 times lower operating voltage. Thanks to this, power dissipation is hardly a problem, which

makes these lasers more adapted for field instruments. Moreover, the slope efficiency (output laser

power versus injection current) is lower than for both diode lasers and QCLs (a factor 10 compared to

QCLs), while the current and temperature tuning coefficients are much larger. This allows rapid

acquisition of spectra over wider spectral regions.

Here we present two applications of ICL coupled with OF-CEAS at 4.015 µm. The first is SO2 trace

analysis, where we could achieve a detection limit down to ppbv concentration levels with a

response time of a few seconds [3]. As a second application, we report on accurate measurements

and temperature dependence of the water vapor self-continuum absorption. The obtained results

are compared to the MT_CKD model of the water continuum widely used in radiative transfert

models of our atmosphere.

Acknowledgments: This work has the support of the French Agence Nationale de la Recherche

(Breath-Diag project: ANR-15-CE18-0006-01).

References

[1] J. Morville, D. Romanini, and E. Kerstel, in Cavity-Enhanced Spectroscopy and Sensing, edited by G.

Gagliardi and H.-P. Loock (Springer Berlin Heidelberg, 2014), pp. 163–209.

[2] J. Morville, S. Kassi, M. Chenevier, and D. Romanini, Appl. Phys. B 80, 1027 (2005).

[3] L. Richard, I. Ventrillard, G. Chau, K. Jaulin, E. Kerstel, and D. Romanini, Appl. Phys. B 122, 247

(2016).


35


Mid-infrared cavity-enhanced continuous-filtering Vernier spectroscopy using a

femtosecond optical parametric oscillator

Amir Khodabakhsh1, Lucile Rutkowski1, Jérôme Morville2, Grzegorz Soboń1,3, Chuang Lu1, and Aleksandra Foltynowicz1

1Department of Physics, Umeå University, Umeå, Sweden

2Institut Lumière Matière, CNRS UMR5306, Université de Lyon, Villeurbanne, France 3Faculty of Electronics, Wrocław University of Science and Technology, Wrocław, Poland

We demonstrate a fast and robust broadband mid-infrared spectrometer based on continuous

Vernier filtering of a frequency comb that acquires high signal-to-noise spectra with 300 nm of

bandwidth in 25 ms in the important fingerprint region around 3.3 µm [1,2]. The spectrometer is

based on a femtosecond doubly resonant optical parametric oscillator, an enhancement cavity, a

rotating diffraction grating, a D-mirror and two photodiodes [2]. It records the entire spectrum of the

signal comb (3.1-3.4 µm) in 25 ms with 8 GHz resolution, sufficient for resolving molecular lines at

atmospheric pressure and for multispecies detection, with frequency scale calibrated using a Fabry-

Perot etalon. Panel (a) shows the normalized spectrum of a dry air sample (in black) containing 2

ppm of CH4 and 110 ppm of H2O. The concentrations are retrieved by fitting a model of the Vernier

spectrum [3] of CH4 (in blue) and H2O (in red) to the measured spectrum. The Allan-Werle plot of the

CH4 concentration retrieved from fits is shown in panel (b) yielding a minimum detectable

concentration of 2 ppb in 25 ms, averaging down to 90 ppt after 16 s. The figure of merit of the

spectrometer is 2×10−9 cm−1 Hz−1∕2 per spectral element, limited by the detector noise. Compared to

other mid-infrared comb-based techniques, the Vernier spectrometer provides the widest spectral

coverage in a short acquisition time using a compact detection system.

Figure: (a) Spectrum of dry air (black, 10 averages) with a fit of the model spectra of CH4 (blue) and

H2O (red), and residual (below). (b) Allan–Werle plot of the minimum detectable CH4 concentration

(black) and the linear fit to the white-noise-dominated regime (red).

Acknowledgments: This work was supported by the Swedish Research Council (621-2012-3650), the

Swedish Foundation for Strategic Research (ICA12-0031), and the Knut and Alice Wallenberg

Foundation (KAW 2015.0159).

References

[1] A. Khodabakhsh et al., Opt. Lett. 41, 2541 (2016).

[2] A. Khodabakhsh, L. Rutkowski, J. Morville, and A. Foltynowicz, arXiv:1702.00396 (2017).

[3] L. Rutkowski and J. Morville, J. Quant. Spectrosc. Radiat. Transf. 187, 204 (2017).

(a) (b)


36


DETERMINATION OF THE OSCILLATOR STRENGTHS FOR THE THIRD AND FOURTH

VIBRATIONAL OVERTONE TRANSITIONS IN SIMPLE ALCOHOLS

Jens H. Wallberg1 and Henrik G. Kjaergaard1

1University of Copenhagen, Department of Chemistry, Universitetsparken 5, 2100 Copenhagen Ø,

Denmark

Absolute measurements of the weak transitions require sensitive spectroscopic techniques.

With our recently constructed pulsed cavity ring down (CRD) spectrometer, we have recorded the

third and fourth vibrational overtone of the OH stretching vibration in a series of simple alcohols:

methanol (MeOH), ethanol (EtOH), 1-propanol (1-PrOH), 2-propanol (2-PrOH) and tert-butanol

(tBuOH). The CRD setup (in a flow cell configuration) is combined with a conventional FTIR

spectrometer to determine the partial pressure of the alcohols from the fundamental transitions of

the OH-stretching vibration. The oscillator strengths of the overtone transitions are determined from

the integrated absorbances of the overtone spectra and the partial pressures.

Furthermore, the oscillator strengths were calculated using vibrational local mode theory with

energies and dipole moments calculated at CCSD(T)/aug-cc-pVTZ level of theory. We find a good

agreement between the observed and calculated oscillator strengths across the series of alcohols.

Figure: The fourth overtone of the OH stretching vibration in methanol (right) along with the

corresponding fundamental OH stretching vibration used for determining the partial pressure (left).


37


Response of optical cavity to amplitude switching, phase shifting and frequency detuning

of incident light

Szymon Wójtewicz, Agata Cygan, Jolanta Domysławska, Katarzyna Bielska, Piotr Masłowski, Roman

Ciuryło, and Daniel Lisak

Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in

Toruń, Grudziadzka 5, 87-100 Torun, Poland

High quality spectroscopic measurements require very precise and accurate determination of both

frequency and absorption axes. Whereas the recent developments in optical metrology have

tremendously improved the frequency axis determination, the absorption axis is typically based on

intensity measurements which are subject to instrumental errors limiting the spectrum quality. One

of the most accurate spectroscopic techniques is the cavity ring-down spectroscopy (CRDS) which

relies on the determination of the photons lifetime inside the optical cavity.

We used the CRDS spectrometer [1] with an acousto-optic modulator (AOM) as the light switch. The

electronic system enables controlled frequency detuning from the cavity resonance center,

amplitude switching, and phase shifting of the incident light. We examined the dependence of the

optical cavity response to these effects. A simple analytical model [2] is confronted with our

experimental results. We tested our predictions by changing the amplitude and phase of the RF

signal driving the AOM when it was turned off. We found an excellent agreement with presented

model. We also present systematic measurements of the ring-down decays behavior associated with

the detuning of AOM-shifted beam frequency from the cavity resonance center. For example, in the

case of 65 dB attenuation of the RF signal we observed systematic difference of 0.5% in the ring-

down time constant when the laser frequency detuning from the cavity mode center is 1.2 cavity

mode width. We show that in the extreme situations both the cavity pumping and decay signals can

significantly differ from the exponential rise and decay functions, respectively. These effects may play

an important role in precise CRDS measurements, e.g. in the frequency-agile rapid-scanning (FARS)

CRDS setups [3].

Acknowledgments: The research is part of the program of the National Laboratory FAMO in Toruń,

Poland. The research is supported by the National Science Centre, Poland, Project Nos.

2014/15/D/ST2/05281 and 2015/17/B/ST2/02115.

References

[1] A. Cygan, S. Wójtewicz, G. Kowzan, M. Zaborowski, P. Wcisło, J. Nawrocki, P. Krehlik, Ł.

Śliwczyński, M. Lipiński, P. Masłowski, R. Ciuryło, and D. Lisak, J. Chem. Phys. 144, 214202 (2016).

[2] J. Morville, D. Romanini, M. Chenevier, and A. Kachanov, Appl. Opt. 41, 6980 (2002).

[3] G.-W. Truong, K. O. Douglass, S. E. Maxwell, R. D. van Zee, D. F. Plusquellic, J. T. Hodges, and D. A.

Long, Nature Photon. 7, 532 (2013).


38


3- Mirror Off-Axis Integrated Cavity Output Spectroscopy at Near- and Mid-Infrared

Wavelengths

Faisal Nadeem1, Julien Mandon

1, Simona M. Cristescu

1 and Frans J.M. Harren

1

1Trace Gas Research Groupy, Molecular and Laser Physics, Institute for Molecules and Materials, Radboud

University, Nijmegen, the Netherlands

Since its development two decades ago, Integrated Cavity Output Spectroscopy (ICOS) has a fast growing application for trace gas sensing [1]. Due to non-resonant coupling of the light, constant power throughout the optical cavity can be achieved with a simple, stable and robust design, with no need to lock the laser to the cavity [2]. However, mid-infrared detectors have limited sensitivity[3], as a result very high reflective mirrors (> 99.95 %) cannot be used, since the throughput intensity from these optical cavities is low and the sensitivity of the system will be limited by the noise floor of the detector. As a result, mirrors with extreme high reflectivity cannot be used in ICOS and a maximum obtainable effective path length cannot be reached from this method. Optical re-injection was introduced recently to overcome this drawback[4]. A third mirror with a small entrance hole to couple the incoming laser beam can build up throughput intensity onto the detector and ultimately on the sensitivity of the optical set-up [4-6].

Here, we used a novel 3-D ray-tracing vector model to simulate the optical re-injection effect in non-resonant optical cavities, The model includes radii of curvature of the cavity mirrors, mirror diameter, cavity and re-injection cavity length, incoming beam entrance angles, positions, hole size and spot pattern analysis on the mirrors surfaces. The model takes into account astigmatism. Further optimization has been done by using a Genetic Algorithm for the parameters. Throughput intensity enhancement factors of 101 and 1400 are found for short lengths (3 cm) and long cavities respectively (50 cm). To demonstrate this enhancement obtain with by adding a 3rd mirror, we build-up setups in near and mid-infrared. In the near infrared, an external cavity diode laser (1510 - 1630 nm) is used with high finesse cavity of mirrors having ROC of 1 m and reflectivity of 99.8%. In the

mid-infrared an external cavity quantum cascade laser (7-9 m) is used in combination with a high finesse cavity consisting of 3- mirrors having 2-inch diameter, 98 % reflectivity and mirror ROC of 50 cm.

1. O'Keefe, A., J.J. Scherer, and J.B. Paul, cw Integrated cavity output spectroscopy. Chemical Physics

Letters, 1999. 307(5–6): p. 343-349. 2. Paul, J.B., L. Lapson, and J.G. Anderson, Ultrasensitive absorption spectroscopy with a high-finesse

optical cavity and off-axis alignment. Applied Optics, 2001. 40(27): p. 4904-4910. 3. Dhar, N.K., R. Dat, and A.K. Sood, Advances in Infrared Detector Array Technology, in Optoelectronics -

Advanced Materials, S.L. Pyshkin and J.M. Ballato, Editors. 2013, InTech. 4. Leen, J.B. and A. O'Keefe, Optical re-injection in cavity-enhanced absorption spectroscopy. Review of

Scientific Instruments, 2014. 85(9). 5. Centeno, R., S.M. Cristescu, and F.J.M. Harren, Three mirror off axis integrated cavity output

spectroscopy for the detection of ethylene using a quantum cascade laser. Sensors and Actuators B-Chemical, 2014. 203: p. 311-319.

6. Centeno, R., et al., Sensitivity enhancement in off-axis integrated cavity output spectroscopy. Optics Express, 2014. 22(23): p. 27985-27991.


39


Saturated Absorption Modeling in Gas Phase: Dealing with Gaussian Beams

Patrick Dupré1

1Laboratoire de Physico-Chimie de L’Atmosphère, ULCO, Dunkerque, France

We propose a general approach to deal with any shape of the electromagnetic field

interacting with a molecular species (2-level system) under saturation conditions. The

development is specifically applied to Gaussian-shaped beams. To make the resulting

analytical expressions tractable, approximations are proposed. Finally, two or three

numerical integrations are required for describing the Lamb-dip profile. The model allows

us to describe the saturated absorption under low pressure conditions where the transit-

time broadening may overcome the collision rates. The formalism is applied to two specific

overtone transitions of acetylene in the Near-Infrared. We will discuss the simulated line

shapes versus the collision and transit-time rates. Specific limit behaviors will be illustrated

while the transit regimes are mainly controlled by the Rabi frequency. The input

parameters can be recovered by profile fitting. This formalism is specially well adapted to

sub-Doppler spectroscopy in cavity.

Reference

[1] P. Dupré. Saturated Absorption Modeling in Gas Phase: Dealing with Gaussian beams

and Applications, Submitted to J. Quant. Spect. & Rad. Trans.


40

12:00-12:15 2M10 (sponsor presentation)

to be announced

Antoine Müller

Alpes Lasers SA, Avenue des Paquiers 1, CH-2072 St. Blaise, Switzerland,


High performance mirrors for CRD-application made by LAYERTEC

Sören Paulke1 and Dr. Frank Wunderlich1

1LAYERTEC GmbH, Ernst Abbe Weg 1, 99441 Mellingen, Germany

Performance of CRD mirrors not only depends on reflectivity, transmission and absorption losses of

the coating but also on scattering losses mainly caused by the surface of substrates. Therefore it is

reasonable for processing to combine a high precision optics facility with coating technology within

one company. Layertec established this concept together with high end metrology having each

parameter under control and being able to customize optical properties as well as item geometries.

Standard CRD mirrors from UV to MIR range are available from stock with overlapping HR region.

Other R-T combinations or broadband solutions can be customized in economic, small and precise

coating batches.


41


Spectroscopic Solutions for Research Institutes

Lisa Bergson, CEO and Marten Beels

Tiger Optics, 250 Titus Avenue, Warrington, Pennsylvania, 18976, USA

The intrinsic technical advantages of CW-CRDS make it an optimal solution for many of the measurement requirements of National Metrology institutes, as well as government and industrial research labs, around the world. Tiger Optics offers a diverse product portfolio with unprecedented accuracy, repeatability, dynamic range, linearity, and freedom from interferences. We have expertise in working with challenging materials, such as HCl, and in resolving complex spectra, such as H2O in pure NH3. The high sensitivity of Tiger Optics analyzers makes them ideal for purity analysis and validation of zero-gasses. We will provide an overview of Tiger Optics and present some exceptional examples related to advanced research supported with real world data.


42

09:00-09:30 3M1 (invited)

Cavity Ring-Down polarimetry

G. Katsoprinakis1,2, D. Sofikitis1,2, A.K. Spiliotis1,2 T.P. Rakitzis1,2

1 IESL-FORTH, N. Plastira 100, 71110 Heraklion-Crete, Greece 2 Department of Physics, University of Crete, 71003 Heraklion-Crete, Greece

The measurement of (single-pass) chiral optical rotation and circular dichroism is the most widely used method for chirality sensing, and is of fundamental importance to many fields. However, these chiral signals are typically very weak, and their measurement is limited by larger time-dependent backgrounds (such as spurious birefringence) and by imperfect and slow subtraction procedures. Using a novel bow-tie cavity with an intracavity Faraday Effect, we demonstrate three important improvements: (a) the enhancement of the chiral optical

rotation angle by the number of the cavity passes (typically 1000); (b) the suppression of birefringent backgrounds; and (c) the ability to reverse the sign of the chiral signal rapidly, allowing the isolation of the chiral signal from backgrounds [1]. Using chiral cavity ring-down polarimetry, we have demonstrated the measurement of chiral optical rotation in high-noise environments, such as for open-air gas samples, and for chiral liquids in the evanescent wave produced by total internal reflection at a prism surface [2,3]. We discuss new fields of application of chiral sensing, and also report progress towards the measurement of parity nonconserving optical rotation in atomic iodine at 1315 nm [4,5].

References [1] L. Bougas, G. Katsoprinakis, W. von Klitzing, J. Sapirstein, T.P Rakitzis, Phys. Rev. Lett. 108, 210801 (2012). [2] D. Sofikitis, L. Bougas, A. Spiliotis, G. Katsoprinakis, B. Loppinet, T.P. Rakitzis, Nature 514, 76 (2014). [3] L. Bougas, G. Katsoprinakis, D. Sofikitis, A. Spiliotis, P. Tzallas, B. Loppinet, T.P Rakitzis, J. Chem. Phys. 143, 104202 (2015). [4] L. Bougas, G. Katsoprinakis, W. von Klitzing, T.P. Rakitzis, Phys. Rev. A 89, 052127 (2014). [5] G. E. Katsoprinakis, G. Chatzidrosos, J. A. Kypriotakis, E. Stratakis, and T. P. Rakitzis, Sci. Rep. 6, 33261 (2016).


43


Direct broadband measurement of cavity modes using a mechanical Fourier transform

spectrometer with kHz resolution

Lucile Rutkowski1, Alexandra C. Johansson1, Gang Zhao1,2, Thomas Hausmaninger1, Amir

Khodabakhsh1, and Aleksandra Foltynowicz1

1Department of Physics, Umeå University, 901 87 Umeå, Sweden 2Institute of Laser Spectroscopy, Shanxi University, Taiyuan 090006, China

We report direct simultaneous measurement of 16000 cavity resonance modes over a 120 nm

bandwidth in 20 minutes using an Er:fiber frequency comb and a mechanical Fourier transform

spectrometer (FTS) with sub-nominal resolution [1, 2]. The cavity length and the comb are stabilized

to a continuous wave Er:fiber laser locked to a sub-Doppler CO2 transition at 1577 nm using the NICE-

OHMS technique. For recording of the cavity transmission, the comb frequencies are stepped across

the cavity resonances with kHz resolution, as shown in panel (a). By fitting Lorentzian profiles to the

cavity modes [inset in (a)], we retrieve their resonance frequencies, amplitudes and linewidths with

high precision. Panel (b) shows the dispersion of the cavity mirrors and of N2 calculated from the

resonance frequencies of an empty cavity and a cavity filled with the gas, respectively. When the

cavity is filled with an absorbing gas, the dispersive lineshapes of molecular transitions can be

retrieved, as shown in panel (c) for the 3ν1+ν3 band of 1% CO2 in N2 at 750 Torr. Comb-based FTS is

thus a perfect tool for broadband precise characterization of high finesse cavities and intracavity

media. It opens up for accurate measurements of refractive indices of gases, and of both the real and

imaginary parts of entire molecular absorption bands.

Figure: (a) Cavity transmission spectrum, where the individual modes are resolved, inset: a cavity

mode with a Lorentzian fit and residuum. (b) Dispersion of the cavity mirror coatings (left y-axis) and

of N2 at 750 Torr (right y-axis), compared to a model based on the Sellmeier equation. (c) Dispersion

spectrum of CO2 together with a fit of the imaginary part of the complex Voigt profiles using the

HITRAN parameters, and residuum (lower panel).

Acknowledgments: This work has the support of the Swedish Research Council (621-2012-3650 and

2016-03593), the Swedish Foundation for Strategic Research (ICA12-0031), and the Knut and Alice

Wallenberg Foundation (KAW 2015.0159).

References

[1] P. Masłowski, et al., Phys. Rev. A 93, 021802 (2016) [2] L. Rutkowski, et al., arXiv:1612.04808 [physics.ins-det] (2016)


44


A Cavity-Ring-Down Doppler-Broadening Thermometer

Riccardo Gotti1, Luigi Moretti2, Davide Gatti1, Antonio Castrillo2, Gianluca Galzerano1,

Paolo Laporta1, Livio Gianfrani2 and Marco Marangoni1

1Politecnico di Milano and IFN-CNR, Via G. Previati 1/C, 23900 Lecco, Italy 2Università degli Studi della Campania “Luigi Vanvitelli” – Dipartimento di Matematica e Fisica, Viale

Lincoln 5, 81100 Caserta, Italy

The absolute temperature of a CO2 gas sample is measured at few-Pascal pressures by a near-

infrared cavity-ring-down spectrometer exhibiting relevant features for Doppler Broadening

Thermometry (DBT) [1,2], namely speed, sensitivity and accuracy. Speed is obtained through a single-

sideband modulator that can be quickly scanned over cavity resonances. Sensitivity is given by a

cavity-ring-down-spectroscopy (CRDS) approach in a high finesse cavity. Accuracy is ensured by the

referencing of the probe laser to a frequency comb and by the high spectral density of the frequency

axis, which is crucial for the choice of an adequate line-shape model and for an accurate fitting

procedure. This translates into an rms noise of 1.1∙10-11 cm-1 on 4.2-GHz-large comb-referred CRDS

spectra made up of 3000 spectral points and acquired in 9 minutes.

Measurements have been performed in different days on the highly isolated P12e line of the

30012-00001 band of CO2 at pressures from 1 to 7 Pa. In spite of the very low pressure regime,

speed-dependent effects on collisional parameters have been observed and properly taken into

account in the temperature retrieval using a Hartmann-Tran profile (HTP). The differences between

the temperature measured by means of a calibrated pt-100 thermometer and that retrieved from

the multi-spectra fitting procedure are reported in Figure 1 as a function of the integrated

absorbance. These differences always remain below the 50 mK level, i.e. well within the 1-

uncertainty of the adopted temperature sensors. The overall accuracy amounts to 57 ppm and the

precision is 47 ppm. While demanding for more stringent tests in a more accurate thermodynamic

environment, these results represent an extremely promising basis in view of an up-scaling of DBT to

the 1 ppm level.

Figure 1. Difference between temperature retrieved from spectra (Tspec) and temperature measured

by the thermal sensor (Tmeas), as a function of Integrated Absorbance.

References

[1] C. Daussy, M. Guinet, A. Amy-Klein, K. Djerroud, Y. Hermier, S. Briaudeau, C. J. Bord´e, and C. Chardonnet, Phys. Rev. Lett. 98, 250801 (2007). [2] L. Moretti, A. Castrillo, E. Fasci, M. D. De Vizia, G. Casa, G. Galzerano, A. Merlone, P. Laporta, and L. Gianfrani, Phys. Rev. Lett. 111, 060803 (2013).


45

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