Enhancement of second harmonic generation by wavefront shaping in the scratch of BaMgF4 nanocrystal powder film HAOYING WU, ZHUO WANG, HAIGANG LIU, YANQI QIAO, YUANLIN ZHENG, AND XIANFENG CHEN* The State Key Laboratory on Fiber Optic Local Area Communication Networks and Advanced Optical Communication Systems, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China *[email protected]
Abstract: During the exploration of nonlinear crystal, such as BaMgF4 crystal for all-solid-state lasers in the vacuum ultraviolet region, many problems emerged in the scattering centers. These were caused by immature crystal-growth technology, which may bring difficulties to the periodic poling process for quasi-phase-matching. In previous studies, research has shown that nonlinear random materials can also be used for frequency conversion. In this paper, a random nonlinear process was observed when the fundamental wave is illuminated onto the scratch of the BaMgF4 nanocrystal powder film. Then, the second-harmonic waves scattered from the nonlinear turbid media are re-collected to a forward direction using feedback wavefront shaping. The method shows a repeated way to improve the conversion efficiency, which may be viable to improve the second order conversion efficiency of BaMgF4 at other wavelengths, especially in the VUV regime. Additionally, more interesting applications in random nonlinear material, such as nanocrystal ceramics, can be expected in the future.
© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction All-solid-state lasers (ASSLs) have a lot of advantages, such as narrow bandwidth, high beam quality and compact setup compared with currently used excimer laser [1]. Due to these advantages, ASSLs in the vacuum ultraviolet (VUV) have been required for optical lithography, photoelectron spectroscopy and medical uses [2,3]. In 2007, C. Chen et.al. obtained watt-level average-power from 185 nm to 200 nm by using KBe2BO3F2 (KBBF) crystal [3]. Compared with KBBF, a new ferroelectric crystal BaMgF4 (BMF) was found to be another candidate for ASSLs in the VUV and mid-IR region because of its transparency from 125 nm to 13 μm [4,5]. The second-order nonlinear optical coefficient of BMF was reported to be d31 = 0.15 pm/V, d32 = 0.36 pm/V, d33 = 0.12 pm/V [2]. Several years ago, E.G. Villora et al. obtained the shortest frequency-doubling emission at 368 nm by quasi phase matching in BMF crystal [5,6]. Nonetheless, scattering centers are always present in the BMF crystal grown by the temperature gradient technique or the Czochralski method [7,8]. These scattering centers may bring difficulties to the periodic poling process for quasi-phase-matching, and restrict device performance [9]. Besides, the birefringence in these materials was too small to birefringently phase match any interactions to generate VUV [10].
The random nonlinear system has emerged as a new research interest because it does not have strict requirement of crystals. It was demonstrated that the purposeful focusing of a second harmonic generated and scattered from superfine lithium niobate nanocrystal powder via feedback wavefront shaping method [11].
In this paper, the second harmonic generation (SHG) scattered from BMF nanocrystal powders was enhanced by feedback wave-front shaping, and the efficiency can be enhanced
Vol. 8, No. 11 | 1 Nov 2018 | OPTICAL MATERIALS EXPRESS 3593
#345315 Journal © 2018
https://doi.org/10.1364/OME.8.003593 Received 7 Sep 2018; revised 20 Oct 2018; accepted 22 Oct 2018; published 29 Oct 2018
by 30 times. obviously whreason is that also played an
2. ExperimeThe BMF nashown in Figwith maximufabricated by m× m30 mmin Fig. 1(d).
Fig. 1μm). sampl
The feedbcharacterize sin Fig. 2 [15](SLM), then tSLM were dMeanwhile, tserved as a fesome phase malgorithm choSH intensity amutagenic facthe optimizatigeneration. Fi
Additionally,hen the pump p
the rough frinn important rol
ent and resulanocrystal powg. 1(a), the scaum size of ~10
electrophoretic× 0.2 mm as s
1. (a) A SEM imag(b)the Electropho
le. (d) an SEM ima
back wavefronscattering medi]. The fundamthe SH can bedivided into sthe SH intensiteedback to opt
masks were genose half of segat the target, actor into the neion process wainally, the rand
, we found thposition was atge of the scratle in the surfac
lts wders were preanning electron0 μm. As depic deposition mhown in Fig. 1
ge of the BMF paoretic Deposition age of the film sam
nt shaping woria is the key of
mental wave (Fe focused to onseveral segmety at one chartimize the SLMnerated randomments from tw
and composed ext generationas repeated, andom speckle wa
hat the SHG ct the scratch ofch not only proe localization o
epared by the n microscope icted by Fig.
method [14]. Th1(c), and the S
articles with maximMethod (c) the
mple (scale bar, 2 μ
rking as a phaf this study. ThW) was reshap
ne point. Durinents, which crge coupled deM phase mask
mly as the primwo masks whic
the next gener, there came a
nd the spot couas focused into
conversion efff the BMF powovided additionof fundamenta
chemical synt(SEM) picture1(b), the BMF
he layer sampleSEM image of
mum size of ~10 picture of BMF μm).
ase-control hohe concept of tped using the ng the optimizcan reshape thevice (CCD) pks via genetic mal generation.ch were the moration. After in
a new set of SLuld be increasino one point.
ficiency was pwder film. Thenal scattering e
al light [12].
thesis method e of the BMF F nanocrystal e had a dimensthat sample w
μm (scale bar, 50nanocrystal film
olographic techthis technique spatial light m
zation, the pixehe FW indeppixel was recoalgorithm [11] Then, the optost effective rancorporating 1LM phase masngly clearer af
promoted e possible effect but
[13]. As particles
film was sion of 30 as shown
0 m
hnique to is shown
modulator els on the pendently. orded and ]. Firstly, imization
anking by 0%~30%
sks. Next, fter every
Vol. 8, No. 11 | 1 Nov 2018 | OPTICAL MATERIALS EXPRESS 3594
The schemdiode-pumpedof 1064 nm, aa Glan-Taylorpump light tcollimating ashaped wave another lens-transmission awas monitorespectral resolmeasured by filter of 1064computer base
Fig. 3bloomL3(a\b
When thewhich could bdiscussed in tpoints on the 1080 pixels oshown in Figonly one segmby 15 times, a
Fig. 2. The con
matic diagram d all-solid-statea pulse width or Prism were uto fit the inteand beam-bloo
went throughsystem and anand reflection
ed and analyzedlution 1/4 0.09an optical ins
4 nm. All the ed on the gene
3. the schematic ming lens system: b), f2(a\b) = 100, 4
FW was illumbe observed inthe next part. CCD. Then, t
on the SLM w. 4(b), after 20ment in size. Bas shown in Fi
ncept of SHG focu
of the experime Q-switched l
of 10 ns and repused to controlnsity thresholming lens sys
h a dichroic mn ocular glassdirection. In thd by a high-res9 nm). The imstrument CCD
SLM, CCD atic algorithm.
diagram of the pL1(a\b), f1(a\b) =40 mm, f3(a\b) = 2
minated onto tn all directionsAt the beginn
the SH signal were divided in00 generations Besides, the intig. 5(a). Accor
using via feedback-
mental setup islaser was usedpetition freque the optical pod and phase stem, the FW mirror and focs. The scatterehe transmissionsolution spectrmage of SH si
(DAHENG Mand spectrome
primary optical se 40, 200 mm; bea200, 50 mm; M, m
the scratch of s, and the possning, the speckwas focused b
nto 160× 90 seoptimization,
tensity of SH arding to the tre
-based wave-front
s illustrated ind as the FW souency of 500 Hzower and the prequirement owas expanded
cused into the ed SH signal n direction, therometer (AUaSignal in the re
MER-131-210Ueter were real-
etup. / 2λ , half-wam-scaling lens sy
mirror; DM, dichro
the film, we gsible reason ofkle patterns weby wavefront segments to resa SH focus wat the focused
end of the curv
t shaping.
n Fig. 3. A higurce with a wa
z. A half-wave olarization sta
of the SLM. d to fit the S
BMF film sawas collected
e intensity of SSpec 2048-FT, eflection direc
U3M/C) after p-timely monito
wave plate; beam-ystem: L2(a\b) andic mirror; F, filter.
got the brightef this phenomeere a group of
shaping. Firstlyshape the SH w
was observed wlocation was
ve, further impr
gh-energy avelength plate and tes of the Across a LM. The ample by d in both SH signal Avantes,
ction was passing a
ored by a
-d .
est signal enon was f discrete y, 1920×wave. As
which was enhanced rovement
Vol. 8, No. 11 | 1 Nov 2018 | OPTICAL MATERIALS EXPRESS 3595
of optimizatioenhancement get a clearer Swere set to 3estimated to b
The enhanchosen positioOne is the qoptimization. enhancement As shown in Fintensity at thvalue for gene
The possiscattered SH on the scratcha possibly per
Fig. 4optimgenerafocus segme
on was possiblwas similar to
SH speckle pat300. Finally, be 8 pixels, as sncement factoron before and
quantity of segThe other is factor has a th
Fig. 5(c), after he focused locetic algorithm. ible reason fosignal was focu
h of the film sarfect-focusing p
4. (a)(c)(e) picturmization while the p
ations of optimizaafter 300 genera
ents.
le. Thus, the go the previous ottern, the segmthe speckle pshown in Fig. 4r η was used tafter optimiza
gments, becauthat η increas
hreshold with th300 generation
cation was estim
or the SH focuused outside th
ample might plprocess [16].
res before optimipixels were divideation while the pixations of optimiza
generations weone, as shown
ments were refiatterns turned 4(f). to describe theation. There ar
use image thinses with the ghe definite genns optimizationmated to be 3
using based ohe surface [11]lay an importan
zation (b) The Sed into 160 × 90 sexels were divided ation while the p
ere increased toin Fig. 4(d) an
ined to 240× 1d into a focal
e relative intenre two main innning can impgenerations untneration and thn, the enhancem0, which migh
on this techno]. Additionallynt role in this o
SH focus after 20egments. (d) The Sinto 160 × 90 segmixels were divide
o 300, but thend Fig. 5(b). In35, and the gepoint, and th
nsity of the sinfluencing factprove the effictil saturation [
he quantity of sment factor η oht be a local m
ology is that r, the multiple soptimization, l
00 generations ofSH focus after 300ments. (f) The SHed into 240 × 135
result of n order to enerations he size is
ignal in a tors of η. ciency of [11]. The segments. of the SH maximum
randomly scattering leading to
f 0 H 5
Vol. 8, No. 11 | 1 Nov 2018 | OPTICAL MATERIALS EXPRESS 3596
Fig. 5after estima(c) η wsegme
This expenonlinear matbe realized ingeneration, fo
3. DiscussioDuring the exabout several influenced bypulse intensitbecause of thmW/mm2. Howhen the pumspectrometer, moved the fofilm, as shown
Fig. 6part oFW mfigure
. (a) The enhancem200 generations ated to be 15 afterwas estimated to bents.
riment is belieterials, nanotubn other nonlineour-wave mixin
on xperiment, the S
nW/mm2. Besy the intensity ty, but found he thermal effowever, duringmp position fo
a typical enhcus point fromn in Fig. 6.
6. The blue line shof the BMF nanocrmoves to a scratch e (scale bar, 100 μm
ment factor η of thwhile the pixels
r 300 generations wbe 30 after 300 gen
eved to be repebe materials anear processes wng and stimulat
SH signal coulsides, the efficof the incidenthat the surfa
fect accumulag the experimecused at the s
hancement in om the temper pa
hows the intensity rystal film. The reof this film. The mm).
he SHG at the focuwere divided in
while the pixels wnerations while the
eatable in othend other nanocwith proper coted Raman sca
ld be measuredciency of wavent light. Thereace of the BMtion [17]. Theent, it was foucratch of the Bour experimenart of the BMF
of the SH signal wed line shows the microscopic image
used location was nto 160 × 90 segmwere divided into 1e pixels were divid
er nonlinear macrystal materialonfigurations, attering, etc.
d at the film, buefront shapingefore, we triedMF film sample damage threund that the SBMF powder
nts was estimatF nanocrystal f
when the FW focuintensity of the SHe of the scratch is
estimated to be 15ments. (b) η was60 × 90 segments
ded into 240 × 135
aterials, such als. It is also exsuch as third h
ut the intensityg technology isd to increase thle would be deshold was abSH signal wasfilm. Monitoreted to be 100 film to a scratc
uses on the temperH signal when thealso shown in this
5 s . 5
as porous xpected to harmonic
y of it was s strongly he pump-destroyed bout 22.1 s stronger ed by the after we
ch of this
r e s
Vol. 8, No. 11 | 1 Nov 2018 | OPTICAL MATERIALS EXPRESS 3597
To undersMultiphysics.intensity waspowder accumfocus on this s
Fig
Theoreticathe rough surfAs the studyproportion to
where Ipoly is coherent feedat the accumusurface may a22].
4. ConclusioIn conclusiondeposition meilluminated onrough surfacewhich is in dishaping methThe enhancemAt last, the SHorders of maefficiency basrepeated in Btowards VUV
Funding National KeyFoundation oTechnology o
References 1. L.J. Cox, Sol2. J. J. Chen, X
second-order3. T. Kanai, X.
KBBF prism
stand the defec As shown in
s randomly enmulated and fstructure, and i
. 7. The intensity o
ally, there werface caused mu
y on random the effective o
the total SH idback was moreulating area coalso help form
on n, the BMF nethod. The SHnto the scratche caused multiirect proportionod based on th
ment factor at HG efficiency agnitude. Thissed on the ran
BMF nanocrysV.
y R&D Progrf China (NSFC
of Shanghai (17
lid-State Laser EnX. F. Chen, Y. Z. M
r nonlinear opticalWang, S. Adachi,
m-coupled device,”
ct-enhancemenn Fig. 7(a), thnhanced at theformed a roughit was also enh
of both the FW wa
re two main reultiple scatterinnonlinear mat
optical path [18
I
intensity; I0 is e likely to be eompared with t
m a surface loc
nanocrystal powH intensity wash of the film. Tiple scatteringn to the secondhe genetic algothe focused loof BMF nanoc
s work providndom nonlineatal ceramic, w
ram of ChinaC) (11734011)7JC1400400).
gineering (SpringMa, Y. L. Zheng, Al coefficients of Ba, S. Watanabe, and
” Opt. Express 17(
nt effect, we sihe result of th
edge of the h surface. Fur
hanced locally,
ave and SHG was r
easons for this ng, so that the terials shows,
8,19], and the e
0 ,polyI I L∝
the FW intensestablished withthe temper paralization aggre
wder film wass enhanced by
The possible rea, so that the e
d-harmonic inteorithm, the SHcation was appcrystal powder des a repeatabar material. Thwhich can imp
a (2017YFA0); The Foundat
er, 1997). A. H. Wu, H. J. Li,aMgF4,” J. Opt. Sod C. Chen, “Watt-l10), 8696–8703 (2
imulated the prhe simulation scratch where
rthermore, the as shown in F
randomly enhance
phenomenon.effective opticthe total SH
equation can be
sity; L is the oh the help of lort of the samplegating both F
s prepared usy nearly 100 timason of this pheffective opticensity. Using t
H signal was foproximately 30r film can be enble way to inhe experiment prove the SHG
0303700); Nattion for Devel
, L. W. Jiang, and oc. Am. B 29(4), 6level tunable deep2009).
rocess using Cof the SH sig
e the BMF na FW was sim
Fig. 7(b).
ed at the scratch.
The first onecal path becam
H intensity is e written as:
optical path. Tonger interactile. Secondly, t
FW and SH po
ing the electrmes when the
henomenon wacal path becamthe feedback wocused to a brig0 after 300 gennhanced by neancrease the co
is also expecG conversion e
tional Naturallopment of Sci
J. Xu, “Measurem665–668 (2012). p ultraviolet light s
COMSOL gnal. The anocrystal
mulated to
was that me longer.
in direct
Therefore, on length the rough
ower [20–
ophoretic FW was
as that the me longer wave-front ght point. nerations. arly three onversion ted to be efficiency
Science ience and
ment of
ource by a
Vol. 8, No. 11 | 1 Nov 2018 | OPTICAL MATERIALS EXPRESS 3598
4. S. C. Buchter, T. Y. Fan, V. Liberman, J. J. Zayhowski, M. Rothschild, E. J. Mason, A. Cassanho, H. P. Jenssen, and J. H. Burnett, “Periodically poled BaMgF4 for ultraviolet frequency generation,” Opt. Lett. 26(21), 1693–1695 (2001).
5. K. Shimamura, E. G. Villora, H. R. Zeng, M. Nakamura, S. Takekawa, and K. Kitamura, “Ferroelectric properties and poling of BaMgF4 for ultraviolet all solid-state lasers,” Appl. Phys. Lett. 89(23), 232911 (2006).
6. E. G. Víllora, K. Shimamura, K. Sumiya, and H. Ishibashi, “Birefringent- and quasi phase-matching with BaMgF4 for vacuum-UV/UV and mid-IR all solid-state lasers,” Opt. Express 17(15), 12362–12378 (2009).
7. M. Halugka, H. Kuzmany, M. Vybornov, P. Rogl, and P. Fejdi, “A double-temperature-gradient technique for the growth of single-crystal fullerites from the vapor phase,” Appl. Phys., A Mater. Sci. Process. 56(3), 161–167 (1993).
8. A. Lipchin and R. A. Brown, “Comparison of three turbulence models for simulation of melt convection in Czochralski crystal growth of silicon,” J. Cryst. Growth 205(1–2), 71–91 (1999).
9. A. H. Wu, Z. Wang, L. B. Su, D. P. Jiang, Y. Q. Zou, J. Xu, J. Chen, Y. Ma, X. Chen, and Z. Hu, “Crystal growth and frequency conversion of BaMgF4 single crystal by temperature gradient technique,” Opt. Mater. 38, 238–241 (2014).
10. M. N. Valdez, H. Th. Spanke, and N. A. Spaldin, “Ab initio study of the ferroelectric strain dependence and 180◦ domain walls in the barium metal fluorides BaMgF4 and BaZnF4,” Phys. Rev. B 93(6), 064112 (2016).
11. Y. Qiao, Y. Peng, Y. Zheng, F. Ye, and X. Chen, “Second-harmonic focusing by a nonlinear turbid medium via feedback-based wavefront shaping,” Opt. Lett. 42(10), 1895–1898 (2017).
12. N. Garcia and A. Z. Genack, “Anomalous photon diffusion at the threshold of the Anderson localization transition,” Phys. Rev. Lett. 66(14), 1850–1853 (1991).
13. S. Fujihara, Y. Kishiki, and T. Kimura, “Sol-gel processing of BaMgF4-Eu2+ thin films and their violet
luminescence,” J. Alloys Compd. 333(1), 76–80 (2002). 14. M. Taheri, H. Abdizadeh, and M. R. Golobostanfard, “Formation of urchin-like ZnO nanostructures by sol-gel
electrophoretic deposition for photocatalytic application,” J. Alloys Compd. 725, 291–301 (2017). 15. L. P. Wan, Z. Y. Chen, H. L. Huang, and J. X. Pu, “Focusing light into desired patterns through turbid media by
feedback-based wavefront shaping,” Appl. Phys. B 122(7), 204 (2016). 16. I. M. Vellekoop, A. Lagendijk, and A. P. Mosk, “Exploiting disorder for perfect focusing,” Nat. Photonics 4(5),
320–322 (2010). 17. S. Zhu, Z. Shen, B. Jiang, and X. Chen, “Random lasing at the edge of a TiO2 nanotube thin film,” Appl. Opt.
55(19), 5091–5094 (2016). 18. E. Yu. Morozov, A. A. Kaminskii, A. S. Chirkin, and D. B. Yusupov, “Second optical harmonic generation in
nonlinear crystals with a disordered domain structure,” JETP Lett. 73(12), 647–650 (2001). 19. E. V. Makeev and S. E. Skipetrov, “Second harmonic generation in suspensions of spherical particles,” Opt.
Commun. 224(1-3), 139–147 (2003). 20. K. F. Ferris and S. M. Risser, “Surface defect enhancement of local electric fields in dielectric media,” Chem.
Phys. Lett. 234(4–6), 359–366 (1991). 21. X. J. Liu, C. Song, F. Zeng, and F. Pan, “Donor defects enhanced ferromagnetism in Co ZnO films,” Thin Solid
Films 516(23), 8757–8761 (2008). 22. B. B. Straumal, A. A. Mazilkin, S. G. Protasova, P. B. Straumal, A. A. Myatiev, G. Schütz, E. J. Goering, T.
Tietze, and B. Baretzky, “Grain boundaries as the controlling factor for the ferromagnetic behaviour of Co-doped ZnO,” Philos. Mag. 93(10–12), 1371–1383 (2013).
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