Improved fourth harmonic generation in β-BaB2O4 by tight elliptical focusing perpendicular to walk-off plane

Takahashi, Masakuni; Osada, Akira; Dergachev, Alex; Moulton, Peter F.; Cadatal-Raduban, Marilou; Shimizu, Toshihiko; Sarukura, Nobuhiko

doi:10.1016/j.jcrysgro.2010.10.082

Cited by 20 publications

(13 citation statements)

References 5 publications

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“…First, both these values are below 0.06 cm -1 , which is low compared to the 0.143 cm -1 previously reported for flux-grown BBO [7]. In high power experiments even a small absorption can induce a thermal dephasing strong enough to lower the conversion efficiency significantly [8]. A second remark is that the CZ BBO has a slightly higher linear absorption than the flux-grown crystal, which indicates that CZ growth itself is not enough to guarantee a lower absorption than a flux grown BBO.…”

Section: Absorption and Second Harmonic Generation Measurementsmentioning

confidence: 63%

Impact of BaB2O4 growth method on frequency conversion to the deep ultra-violet

Deyra

Maillard

et al. 2015

Solid State Sciences

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To cite this version:Loic Deyra, Alain Maillard, R Maillard, D Sangla, F Salin, et al.. Impact of BaB 2 O 4 growth method on frequency conversion to the deep ultra-violet. Solid State Sciences, Elsevier, 2015, 50, pp.97-100. 10 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Czochralski and TSSG β-BBO crystals are compared for high power UV (266nm) in second harmonic generation. Impurities from flux decrease the efficiency of harmonic generation at high power (40%). Corresponding author : A Maillard, alain.maillard@univ-lorraine.fr M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT Impact of BaBAbstract: In this article, we report how the growth method used for barium beta-borate β−BaB2O4 (BBO) impacts its high power second harmonic generation properties in the deep-UV. We compared a BBO crystal grown by flux (Top Seeded Solution Growth or TSSG) and a BBO crystal grown by the Czochralski (CZ) method. We first characterized their transparency properties, then we measured their single-pass second harmonic conversion efficiencies with both a low average power and a high average power nanosecond pulsed lasers. We show that both crystals have comparable linear absorption and conversion efficiencies at low power, whereas in a high power experiment, the CZ-grown BBO yields higher conversion efficiency than the TSSG grown BBO. With a 30 W, 150 kHz, 8ns green laser, the use of a CZ BBO led at best to a 40% increase in available average output power at 257 nm.Keywords: Borates, Nonlinear optical, Czochralski growth, Solution growth, Second harmonic generation. IntroductionThe material machining industry has continuously looked to process more and more types of materials efficiently. For some of them such as silicon, glass, sapphire, the ultraviolet lasers (UV) were developed in order to increase the material absorption [1,2]. While UV lasers around 350 nm obtained by third harmonic generation (THG) are now commonly used in material processing, deep-UV lasers obtained by fourth harmonic generation (FHG) around 260 nm are still challenging to realize. The nonlinear material quality is a key parameter in order to reach high and stable conversion efficiency by reducing thermal dephasing and degradation effects. Beta-barium borate β-BaB2O4 (BBO) is a nonlinear crystal that has good properties for frequency conversion to the UV, such as a high nonlinearity or a short cut-off wavelength in the UV around 190nm [3]. It is available commercially, and is usually grown by top-seeded solution growth (TSSG) assisted with either a Na2O or NaF flux [4]. BBO can be also grown without flux by the Czochralski (CZ) method, but...

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Section: Absorption and Second Harmonic Generation Measurementsmentioning

confidence: 63%

Impact of BaB2O4 growth method on frequency conversion to the deep ultra-violet

Deyra

Maillard

et al. 2015

Solid State Sciences

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“…Despite the elliptic nature of the generated UV beam due the spatial walk-off in BBO, we used cylindrical optics to circularize the beam, obtaining a circularity of >90%. Further improvements in the UV output power could be expected by using fluxless BBO with improved crystal quality [7], multiple short crystals [18], and elliptic focusing [6,13].…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, BBO is known to exhibit two-photon absorption or dynamic color center formation, particularly when generating UV radiation at 266 nm [6], which could be a serious limiting factor at repetition rates as high as ~80 MHz used in this work. Hence, to further study these UV-induced thermal effects, we performed transmission measurements at different temperatures using the 10-mm-long BBO crystal to estimate the two-photon absorption coefficient in BBO.…”

Section: Two-photon Absorption At 266 Nm In Bbomentioning

confidence: 99%

“…However, linear and two-photon absorption, as well as dynamic color center formation [6,7] in BBO, are significant limitations for high-power, high-repetition-rate UV generation, leading to thermal effects [8][9][10][11]. Hence, it is important to carefully study the performance characteristics of BBO for high-power, high-repetition-rate pulse generation in the UV at 266 nm.…”

Section: Introductionmentioning

confidence: 99%

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High-power, high-repetition-rate performance characteristics of β-BaB_2O_4 for single-pass picosecond ultraviolet generation at 266 nm

Kumar¹,

Casals²,

Wei³

et al. 2015

Opt. Express

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Abstract:We report a systematic study on the performance characteristics of a high-power, high-repetition-rate, picosecond ultraviolet (UV) source at 266 nm based on β-BaB 2 O 4 (BBO). The source, based on single-pass fourth harmonic generation (FHG) of a compact Yb-fiber laser in a two-crystal spatial walk-off compensation scheme, generates up to 2.9 W of average power at 266 nm at a pulse repetition rate of ~80 MHz with a single-pass FHG efficiency of 35% from the green to UV. Detrimental issues such as thermal effects have been studied and confirmed by performing relevant measurements. Angular and temperature acceptance bandwidths in BBO for FHG to 266 nm are experimentally determined, indicating that the effective interaction length is limited by spatial walk-off and thermal gradients under high-power operation. The origin of dynamic color center formation due to two-photon absorption in BBO is investigated by measurements of intensity-dependent transmission at 266 nm. Using a suitable theoretical model, two-photon absorption coefficients as well as the color center densities have been estimated at different temperatures. The measurements show that the two-photon absorption coefficient in BBO at 266 nm is ~3.5 times lower at 200°C compared to that at room temperature. The long-term power stability as well as beam pointing stability is analyzed at different output power levels and focusing conditions. Using cylindrical optics, we have circularized the generated elliptic UV beam to a circularity of >90%. To our knowledge, this is the first time such high average powers and temperature-dependent two-photon absorption measurements at 266 nm are reported at repetition rates as high as ~80 MHz. Bradler and E. Riedle, "Sub-20 fs μJ-energy pulses tunable down to the near-UV from a 1 MHz Yb-fiber laser system," Opt.

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“…6, the UV power exhibits a long-term drift resulting in a slow decline from 1.2 W down to ∼1 W after 14 h. By translating the crystal to focus the input beams to a new position inside the BIBO, we could readily recover the maximum UV power. This long-term drift in UV power could be attributed to photo-induced damage [16], two-photon absorption, or dynamic color center formation, previously observed in borate crystals [17]. However, photo-induced damage in BIBO can be repaired with high-temperature annealing at ∼300°C [16], thus potentially improving the long-term power stability.…”

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confidence: 89%

Stable, high-power, Yb-fiber-based, picosecond ultraviolet generation at 355 nm using BiB_3O_6

2015

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We report a stable, high-power, high-repetition-rate, picosecond ultraviolet (UV) source at 355 nm based on singlepass sum-frequency generation of a mode-locked Yb-fiber laser at 1064 nm in the nonlinear crystal BiB 3 O 6 . By performing single-pass second-harmonic generation (SHG) in a 30-mm-long LiB 3 O 5 crystal, up to 9.1 W of average green power at 532 nm is obtained at a single-pass SHG efficiency of 54%. The generated green pulses have a duration of 16.2 ps at a repetition rate of 79.5 MHz, with a passive power stability better than 0.5% rms and a pointing stability <12 μrad over 1 h, in high beam quality. The green radiation is then sum-frequency-mixed with the fundamental in a 10-mm-long BiB 3 O 6 crystal, providing as much as 1.2 W of average UV power, at an infrared-to-UV conversion efficiency of 7.2%, with a passive power stability better than 0.4% rms over 3 h and a pointing stability <45 μrad over 1 h, in TEM 00 spatial profile. . For many years, the development of such ultrafast sources has relied almost entirely on nonlinear optical techniques based on third (∼355 nm) and fourth (∼266 nm) harmonic generation of widely established mode-locked Nd/Yb-doped solid-state lasers at ∼1064 nm. The rapid advances in fiber laser technology in recent years, however, have paved the way for the replacement of bulky, water-cooled, mode-locked solidstate lasers with compact, air-cooled, ultrafast Yb-fiber lasers at ∼1064 nm. With the availability of multiwatt average powers, and the potential for further power scaling, the exploitation of mode-locked Yb-fiber lasers thus offers great promise for the realization of efficient and high-power picosecond UV sources in more practical designs by deploying third and fourth harmonic generation schemes. On the other hand, to fully exploit the advantages of fiber lasers with regard to a compact architecture, simplicity, and portability, it would also be crucial to deploy the most direct nonlinear techniques for UV generation in order to preserve those important merits. To this end, single-pass conversion schemes offer the most effective approach to achieve this goal. We have already verified the viability of such single-pass schemes in combination with continuous-wave (cw) and modelocked Yb-fiber lasers for efficient generation of highpower cw radiation in the green and UV [4], and high-average-power picosecond pulses in the green [5]. Recently, a fiber-based femtosecond green source was also demonstrated [6]. At the same time, a critical factor in the attainment of the highest nonlinear conversion efficiency and output power is the choice of suitable nonlinear materials. For UV generation, this choice is particularly limited and is especially challenging when low-intensity picosecond pulses at high repetition rates are involved. In addition to a wide transparency in the UV, of paramount importance are a sufficiently high effective nonlinearity, low spatial walk-off, high optical damage threshold, low transmission loss, and high optical quality, as well as chemical and the...

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Improved fourth harmonic generation in β-BaB2O4 by tight elliptical focusing perpendicular to walk-off plane

Cited by 20 publications

References 5 publications

Impact of BaB2O4 growth method on frequency conversion to the deep ultra-violet

Impact of BaB2O4 growth method on frequency conversion to the deep ultra-violet

High-power, high-repetition-rate performance characteristics of β-BaB_2O_4 for single-pass picosecond ultraviolet generation at 266 nm

Stable, high-power, Yb-fiber-based, picosecond ultraviolet generation at 355 nm using BiB_3O_6

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