Open Access
Add to BibSonomy
Abstract
We report the generation of picosecond pulsed light at a 266 nm wavelength with an average power of 53 W. We developed a picosecond pulsed 1064 nm laser source with an average power of 261 W, a repetition rate of 1 MHz, and a pulse duration of 14 ps, using a gain-switched DFB laser diode as a seed laser and a 914 nm laser-diode-pumped Nd-doped YVO4 power amplifier. We achieved stable generation of 266 nm light with an average power of 53 W from frequency quadrupling using an LBO and a CLBO crystals. The amplified power of 261 W and the 266 nm average power of 53 W from the 914 nm pumped Nd:YVO4 amplifier are the highest ever reported, to the best of our knowledge.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
All solid-state deep-ultraviolet (DUV) lasers, which combine solid-state laser technologies with frequency conversion technologies, can achieve stable operation with high beam quality, are easy to handle, and have low running costs, so they are expected to be utilized in industrial applications for fine and high-quality processing. DUV light with high photon energy is used in various applications, such as high-brightness gamma-ray generation [1], Raman spectroscopy [2], material processing [3–7], and semiconductor inspection [8]. DUV pulses at high repetition rates in particular are important for many applications; the higher repetition rate and output power can expand the range of applications, from drilling in a micro-area to high-speed cutting. Additionally, DUV solid-state lasers can operate at a higher repetition rate than conventional excimer lasers, making them suitable for processing arbitrary shapes and patterns.
The development of nonlinear optical crystals, β-BaB2O4 (BBO) [9] and CeLiB6O10 (CLBO) [10], in the 1980s and 1990s led to the popularization of high-power DUV solid-state lasers with wavelengths below 300 nm. High-power DUV light have accompanied the progress by improving the quality of nonlinear optical crystals and higher average power of near-infrared lasers. To date, numerous (at least 35) studies of DUV light generation at 257 nm or 266 nm wavelengths above 1 W average power have been reported, as shown in Fig. 1 [5,11–45]. The nonlinear optical crystals used were BBO in 15 studies [5,11–24], CLBO in 13 studies [25–37], KBe2BO3F2 (KBBF) in 1 study [38], LiB3O5 (LBO) in 3 studies [39–41], NaSr3Be3B3O9F4 (NSBBF) in 1 study [42], RbBe2BO3F2 (RBBF) in 1 study [43], and YAB in 1 study [44]. High average power DUV light development is progressing mainly in BBO, CLBO, and LBO crystal, with BBO crystal reported an average power of 20 W in 2020 [24], CLBO 40 W in 2003 [28], and LBO 12 W in 2022 [41]. On the other hand, reports using ultra-fast pulsed lasers with pulse duration of 300 picoseconds or less were 20% of 10 studies from 2000 to 2009, while from 2010 to 2019 it was 56% of 18 studies, and from 2020 to the present it has reached 86% of 7 studies. High-power DUV light is becoming popular with a pulse duration of about 10 ps.
Fig. 1. Performance comparison of 257 nm and 266 nm DUV light in the literature, demonstrating the advantage of our work.
We have been developing fundamental light sources for DUV generation that use a picosecond gain-switched laser diode (LD) and a hybrid fiber and solid-state amplifier, which has a narrower linewidth and high-peak power [31,35–37]. We have also learned that the maximum DUV power used a CLBO crystal in our previous research was mainly limited by the fundamental laser power. In this study, we extended the fundamental power up to 261 W; we used 241 W fundamental power to demonstrate much higher DUV power generation with a maximum average power of 53 W.
High-power ultra-fast pulsed lasers are usually based on Nd-doped media, such as Nd:YAG and Nd:YVO4, or Yb-doped media, such as Yb-doped fiber and Yb:YAG. For ultra-fast pulsed lasers, more than 1.4 kW output power can be demonstrated using a Yb:YAG multi-pass thin disk amplifier. The Nd:YVO4 crystal has the advantage of simplicity in the amplification configuration because it has an emission cross section that is 67 times larger than that of a Yb:YAG crystal, and it has linearly polarized emission, which is ideal for frequency conversion, due to the large birefringence. Since pump LDs in the 800 nm band are required for Nd-doped crystals, the maximum power of the pump LDs is the limiting factor for high-power amplifiers. On the other hand, InGaAs-based LDs emitting in the 900-nm band do not use “Al”, unlike AlGaAs-based LDs emitting in the 800-nm band. This feature allows for higher power LD chips with a higher catastrophic optical mirror damage (COMD) threshold. Therefore, LDs in the 900 nm band used for pumping Yb-doped media can achieve higher brightness and output power than LDs in the 800 nm band used for pumping Nd-doped media [46]. Therefore, thin-disk-type [47] and slab-type [47] high power amplifiers with Yb-doped crystals have been used for picosecond pulse amplification, and conventional end-pumped rod-type amplifiers using Nd crystals have reported maximum power levels of 200 W or less [48]. The side pumping method may allow higher output power for Nd-doped crystals, but it would also degrade the beam quality.
The direct pumping of Nd-doped laser media was proposed to expand the power scaling of Nd-doped laser media [49–59]. In 2003, Sato et al. first reported the direct pumping of Nd-doped media, 4I9/2 → 4F3/2, and shown the possibility of 885 nm and 946 nm pumping of Nd:YAG crystals and 880 nm, 888 nm, and 914 nm pumping of Nd:YVO4 crystals [49]. Delen et al. in 2010 and Bai in 2020 reported on laser operation at different pumping wavelengths for Nd:YVO4, showing that 914 nm pumping is suitable for low-gain amplifiers with high repetition rates [50,51]. However, to date, high-power 1064 nm amplification with 914 nm pumping Nd:YVO4 has not been demonstrated. In this study, we developed two-stage single-pass amplifiers that combine end-pumped rod-type Nd:YVO4 crystals and high-power 914 nm LD modules. We were able to achieve a 1064 nm light with an average power of 261 W, and to generate a 266 nm light with an average power of 53 W by frequency quadrupling using an LBO and a CLBO.
2. Power amplifier with a Nd:YVO4 crystal pumped by 914 nm LD development
2.1 Absorption characteristics at 914 nm and 1064 nm
First, we measured the absorption properties of Nd:YVO4 around 914 nm. The results are shown in Fig. 2. Two Nd:YVO4 crystals 25 mm in length (total length of 50 mm) with a Nd concentration of 0.9at.% were installed in a water-cooled copper holder, and the holder temperature was controlled by controlling the water temperature. A fiber-coupled 914 nm LD module with a core diameter of 200 µm with an NA of 0.22 with an average power of 100 W and a spectral width (FWHM) of 3.3 nm was used to measure the absorption coefficient by launching a 1 mm beam diameter into the Nd:YVO4 crystal using two plano-convex lenses. In Fig. 2(a), the absorption coefficient of Nd:YVO4 was measured by varying the temperature of the LD module from 20 to 40 °C for the center wavelength; the inset shows the spectral width of the laser beam output from the LD module. An absorption coefficient of 0.33 cm-1 was obtained at the center wavelength of 914.5 nm at the temperature of 32 °C. In a previous study [50], 0.58 cm-1 was obtained at a Nd concentration of 1.5at.% with an LD spectral width of approximately 3 nm. This is roughly equivalent to 0.35 cm-1 when converted to 0.9at.% and is consistent with this study.
Fig. 2. Absorption characteristics at 914 nm and 1064 nm of Nd:YVO4: (a) the absorption coefficient at 914 nm band of 0.9at.% Nd:YVO4 (the inset shows the spectral width of the laser beam output from the LD module); (b) temperature dependence of the absorption coefficient of 0.9at.% Nd:YVO4; (c) absorption coefficient at 1064 nm band of 0.9at.% Nd:YVO4 and 0.4at.% Nd:YVO4.
Figure 2(b) shows the dependence of the absorption coefficient on the Nd:YVO4 crystal holder temperature, measured by varying the temperature of circulating water. (Note: The crystal temperature was approximately +20 °C higher than crystal holder temperature at 100 W pumping.) The 914 nm absorption band transition is from the highest Stark sublevel (438 cm-1) of the ground-state manifold of 4I9/2 that is thermally populating [51]. Therefore, the absorption coefficient has a positive coefficient with respect to the crystal temperature, as shown in Fig. 2(b), which is 0.93 × 10−3 cm-1/°C. Figure 2(c) shows the measured absorption coefficient in the 1064 nm band, which peaked at 1064.5 nm with a value of 0.01 cm-1. The disadvantage of the 914 nm pump is the low absorption coefficient of the pump light, and it is necessary to increase the Nd concentration to around 1at.% to obtain sufficient absorption. On the other hand, not only does the absorption at 1064 nm become larger, but the performance as an amplifier is reduced due to quenching, excited state absorption (ESA) [51] and energy transfer upconversion (ETU) [60]. However, it can be useful for power amplifiers, as in this study, where the pulse interval time is much shorter than the excited state lifetime of the upper laser level.
2.2 Experimental setup for the Nd:YVO4 power amplifier pumped by 914 nm LD
Figure 3 shows the configuration of the power amplifier we developed. A homemade picosecond pulsed laser source with an average power of 100 W [36] is used as the seed light source, and the wavelength, pulse duration, beam quality factor, and repetition rate are 1064 nm, 14 ps, 1.4, and 1 MHz, respectively.
Fig. 3. Configuration of the power amplifier. DM1: HR1064/AR 1176 nm dichroic mirror; DM2: HR1064&1176/AR 914 nm dichroic mirror, PBS1, PBS2: polarization beam splitter; HWP1, HWP2: half waveplate, L1-7: lenses.
The 1064 nm beam from the seed source was launched into the Nd:YVO4 crystal module of Amp 1, and the incident beam diameter was adjusted using lenses (L1 and L2). A pair of Nd:YVO4 crystals with a transmitted wavefront distortion of less than λ/6 at 633 nm (peak-to-peak) were used in the Nd:YVO4 crystal module. Since a single long crystal cannot guarantee low-transmitted-wavefront distortion. In addition, crystals of different Nd concentration were employed to suppress the destruction of Nd:YVO4 due to the increase of the injection surface temperature, which is a challenge for high power end pumping. The Nd:YVO4-1 on the pump LD side was 4 × 4 × 20 mm3 with a low Nd concentration of 0.8at.%, and the second Nd:YVO4-2 was 4 × 4 × 15 mm3 with a high Nd concentration of 1.1at.%. A 914 nm LD module with a fiber core diameter of 200 µm with an output power of 370 W, which is commercially available for pump source of Yb-doped fiber lasers, was used as the pump source. The pumping current was suppressed, and the temperature of the LD module was controlled by Peltier elements to reach an oscillation wavelength of 914.5 nm at an average power of 250 W. The beam amplified by Amp1 was launched into the YVO4 crystal module of Amp 2 after adjusting the beam diameter using lenses (L3, L4). The Nd:YVO4-1 on the pump LD side of Amp 2 was 4 × 4 × 20 mm3 with an Nd concentration of 0.8at.%, and the second Nd:YVO4-2 was 4 × 4 × 25 mm3 with an Nd concentration of 0.9at.%. The same type of LD module as in the first stage was used as the pump light source, both having a focusing diameter of 1.8 mm. The beam amplified by Amp 2 was collimated to 2 mm in diameter using lenses (L5-L7).
2.3 Laser performances at 1064 nm
The amplification results are shown in Fig. 4, with Fig. 4(a) showing those for Amp 1. The amplified power was measured at Dump 2, and the beam was adjusted to transmit through PBS1 using a waveplate (HWP1). Transmitted pump power was measured at Dump 1. 174 W of amplified power was obtained with a pump LD power of 252 W. The power transmitted without being absorbed by the Nd:YVO4 module was 79 W, and the absorbed pump power was 173 W. Figure 4(b) shows the amplification results for Amp 2 at an input power of 174 W. The amplified power of 261 W was obtained at an LD output power of 294 W. The power transmitted without being absorbed by the Nd:YVO4 module was 73 W, and the absorbed power was 221 W. Figure 4(c) plots the absorbed pump power on the horizontal axis and the amplified power on the vertical axis; and it shows that slope efficiencies of 58% and 53% were obtained for Amp 1 and Amp 2. Since the transmitted power of pumping is usually less than 10 W for a pump in the 800 nm band, it is thought that more efficient amplification could be achieved by using a longer Nd:YVO4 crystal, increasing the Nd doping concentration, or using a double pass pumping configuration.
Fig. 4. Characteristics of power amplifiers (a) Amp1 and (b) Amp2 as a function of LD pump power, and the (c) amplified power of Amp1 and Amp2 as a function of absorbed pump power.
3. Frequency quadrupling to the stable DUV
3.1 Experimental setup for second- and fourth- harmonic generation
To generate DUV light from 1064 nm to 266 nm, second and fourth harmonics were generated using two nonlinear optical crystals, LBO and CLBO, as shown in Fig. 5. The 1064 nm beam was input into the purge chamber from W1, and launched into an LBO crystal with a length of 15 mm (θ = 90, 0 deg, φ = 0 deg), the LBO crystal was held in a copper holder with a built-in heater, and the holder temperature was set at 148.6 °C. The aperture of the LBO crystal was set to be at least twice the beam diameter defined by 1/e2 of the incident beam, and an aperture (A2) with a φ4 mm diameter aperture was placed just before the LBO crystal. The generated 532 nm beam was reflected by a dichroic mirror pair (DM3) coated with HR532/AR1064 nm and collimated by three lenses (L8∼L10). It was then passed through an attenuator consisting of a half-waveplate (HWP3) and a polarizing beam splitter (PBS3). The 532 nm beam was reflected by a pair of HR532/AR266 nm dichroic mirrors (DM4) and launched into a CLBO crystal with a length of 15 mm (θ = 62.0 deg, φ = 45.0 deg) to generate 266 nm light. The CLBO crystals were grown at Osaka University [61], and the input and output surfaces of the CLBO crystals were not AR-coated to ensure long-term stability. The purge chamber was purging with clean dry air (CDA) to prepend degradation of optics surfaces.
Fig. 5. Configuration of the frequency convertor module. A2: aperture; DM3: HR532/AR1064 nm dichroic mirror; M1: HR532 nm mirror; L8∼L10: lenses; HWP3: half waveplate; PBS3: polarization beam splitter; W1∼W4: AR1064&532 nm window; DM4: HR532/AR266 nm dichroic mirror; DM5: HR266/AR532 nm dichroic mirror; CDA: clean dry air.
3.2 Experimental results
The phase matching angle was adjusted so that the phase matching temperature was 150 °C when the 266 nm power was 5 W. The generated 266 nm beam was reflected by a pair of HR266/AR532 nm dichroic mirrors (DM5), and the output power was measured with a power meter. Figure 6 shows the frequency conversion results, with Fig. 6(a) showing the SHG input/output characteristics. For the 532 nm beam, the waveplate (HWP3) was adjusted, and the beam passing through W3 was measured. At a 241 W fundamental launched into to the LBO, 165 W of 532 nm was obtained with a conversion efficiency of 68%. The inset shows the beam profile at 532 nm with a single peak intensity distribution. Figure 6(b) shows the input/output characteristics of the second SHG, where the incident beam diameter defined by 1/e2 is 7.2 mm and the CLBO crystal holder temperature is adjusted to maximize the 266 nm output for each input power. At a 532 nm input power of 164 W, 266 nm at 53 W was obtained with a conversion efficiency of 32%. The two insets show the beam profiles at 7 W and 53 W average power, indicating that a single peak intensity distribution is maintained at 53 W. The beam quality factor (M2) was measured to be 1.9 at 53 W. M2-200S (Spiricon) was used for the measurement. Figure 6(c) shows the crystal holder temperature dependence of 266 nm power and indicating that the difference in holder temperature at maximum power is 3 °C lower for the case of 5 W of 266 nm power. Therefore, which indicates that 3 °C of heat generation occurs when 51 W of 266 nm light is generated. As shown in our previous study [37], this heat generation exceeds 2.1 °C, which is half the temperature acceptance bandwidth of a 15-mm-long CLBO crystal, preventing high-efficiency conversion. In deep-ultraviolet generation with an average output power exceeding 50 W, the heat generated in the nonlinear optical crystal by absorption (linear and nonlinear) is considered to be the rate-limiting factor for higher output power. Figure 7 shows the free-running results at an average power of 50 W. It can be seen that 50 W was maintained for more than 30 hours without any degradation trend. Furthermore, no degradation of the CLBO crystal was observed before and after running.
Fig. 6. Input and output characteristics of (a) SHG; inset is beam profile at 164 W of 532 nm and (b) FHG; insets are beam profiles at 7 W and 53W of 266 nm, and (c) the temperature characteristic of the CLBO crystal in the FHG stage.
4. Conclusions
We reported the generation of picosecond pulsed light at 266 nm with an average power of 53 W. We amplified a 1064 nm picosecond laser with an average power of 100 W using end-pumped Nd:YVO4 power amplifiers with high brightness 914 nm LDs, and we were able to achieve an average power of 261 W with a slope efficiency of 53% at a repetition rate of 1 MHz Using a 15 mm-long LBO and a CLBO nonlinear crystals with 241 W at 1064 nm, we obtained 165 W at 532 nm with a conversion efficiency of 68%. We also launched a 164 W 532 nm pulse into a CLBO crystal, obtaining an average power of 53 W at 266 nm with a conversion efficiency of 32%. The total conversion efficiency from 1064 nm was 22%, and both the amplified output of 261 W and the average output of 53 W at 266 nm by the 914 nm pumped Nd:YVO4 amplifier are the highest recorded to the best of our knowledge. Further progress in direct pumped end-pump rod amplifiers for Nd-doped media using the 900-nm band LDs and frequency quadrupling are expected to improve performance and reliability for industrial applications.
Funding
New Energy and Industrial Technology Development Organization (JPNP16011, JPNP20017).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. N. Muramatsu, Y. Kon, S. Daté, et al., “Development of high intensity laser-electron photon beams up to 2.9 GeV at the SPring-8 LEPS beamline,” Nucl. Instrum. Methods Phys. Res., Sect. A 737, 184–194 (2014). [CrossRef]
2. Y. Masanori, K. Yuya, T. Yusaku, T. Makoto, T. Eiji, and T. Toshitaka, “A Raman Lidar with a Deep Ultraviolet Laser for Continuous Water Vapor Profiling in the Atmospheric Boundary Layer,” EPJ Web Conf. 237, 03001 (2020). [CrossRef]
3. Y. Imamiya, S. Akama, Y. Fujita, and H. Niitani, “Development of Microfabrication Technology using DUV Laser,” Mitsubishi Heavy Industries Technical Review 53(4), 49–54 (2016).
4. Y. Kawasuji, Y. Adachi, A. Suwa, J. Fujimoto, K. Kakizaki, and M. Washio, “Pulse Width Dependence of Ablation Threshold and Ablation Rate,” in ICALEO 2020 of Micro Session 1 of Laser Material Microprocessing, paper 0442_0638_000138.
5. S. Häfner, C. Wagner, B. Shnirman, M. Ginter, J. Brons, M. Sailer, A. Fehrenbacher, D. Grossmann, D. Flamm, K. Janami, S. Ruebling, U. Quentin, A. Budnicki, I. Zawischa, and D. H. Sutter, “Deep UV for materials processing based on the industrial TruMicro Series of ultrafast solid-state laser amplifiers,” Proc. SPIE 11670, 116701F (2021). [CrossRef]
6. H. Ikarashi, T. Sato, S. Teraki, M. Yoshida, and H. Ozaki, “Low Dk / Df Dielectric Material for 5 G Applications,” in International Conference on Electronics Packaging (ICEP), 117–118 (2022).
7. M. Koh, K. Yoneda, K. Nakada, S. Sekiguchi, S. Mishima, N. Ishikawa, and T. Ogata, “Novel Thermosetting Low Dk/Df Film and Its Performance,” in International Conference on Electronics Packaging (ICEP) (2022), pp. 63–64.
8. H. Nakao, M. Morita, Y. Kaneda, A. Miyamoto, T. Tago, T. Sasa, M. Sasaura, and Y. Furukawa, “High power 4th harmonic generation with optimized enhancement cavity,” in 2017 European Conference on Lasers and Electro-Optics and European Quantum Electronics Conference (2017), paper CA_P_16.
9. C. Chen, B. Wu, A. Jiang, and G. You, “A new type ultraviolet SHG crystal β-BaB2O4,” Science in China 28(3), 235–243 (1985).
10. Y. Mori, I. Kuroda, S. Nakajima, T. Sasaki, and S. Nakai, “New nonlinear optical crystal: Cesium lithium borate,” Appl. Phys. Lett. 67(13), 1818–1820 (1995). [CrossRef]
11. L. B. Chang, S. C. Wang, and A. H. Kung, “Efficient compact watt-level deep-ultraviolet laser generated from a multi-kHz Q-switched diode-pumped solid-state laser system,” Opt. Commun. 209(4-6), 397–401 (2002). [CrossRef]
12. J. Kleinbauer, R. Knappe, and R. Wallenstein, “A powerful diode-pumped laser source for micro-machining with ps pulses in the infrared, the visible and the ultraviolet,” Appl. Phys. B 80(3), 315–320 (2005). [CrossRef]
13. Z. Xiang, J. Ge, Z. Zhao, S. Wang, C. Liu, and J. Chen, “1.9-W flash-lamp-pumped solid-state 266-nm ultraviolet laser,” Chin. Opt. Lett. 7(6), 502–504 (2009). [CrossRef]
14. Q. Liu, X. P. Yan, X. Fu, M. Gong, and D. S. Wan, “High power all-solid-state fourth harmonic generation of 266 nm at the pulse repetition rate of 100 kHz,” Laser Phys. Lett. 6(3), 203–206 (2009). [CrossRef]
15. X. Zhou, D. Yoshitomi, Y. Kobayashi, and K. Torizuka, “1 W average-power 100 MHz repetition-rate 259 nm femtosecond deep ultraviolet pulse generation from ytterbium fiber amplifier,” Opt. Lett. 35(10), 1713–1715 (2010). [CrossRef]
16. S. Y. Zhai, X. L. Wang, Y. Wei, W. D. Chen, F. J. Zhuang, S. Xu, B. X. Li, J. J. Fu, Z. Q. Chen, H. W. Wang, C. H. Huang, and G. Zhang, “A compact efficient deep ultraviolet laser at 266 nm,” Laser Phys. Lett. 10(4), 045402 (2013). [CrossRef]
17. X. Délen, L. Deyra, A. Benoit, M. Hanna, F. Balembois, B. Cocquelin, D. Sangla, F. Salin, J. Didierjean, and P. Georges, “Hybrid master oscillator power amplifier high-power narrow-linewidth nanosecond laser source at 257 nm,” Opt. Lett. 38(6), 995–997 (2013). [CrossRef]
18. C. Chang, K. Hong, P. Krogen, H. Liang, G. Stein, J. Moses, C. Lai, J. Siqueira, L. Zapata, and F. Kärtner, “Multi-mJ, kHz intense picosecond deep ultraviolet source based on a frequency-quadrupled cryogenic Yb:YAG laser,” in Advanced Solid State Lasers, OSA Technical Digest (online) (Optica Publishing Group, 2014), paper ATu3A.3. [CrossRef]
19. S. C. Kumar, J. C. Casals, E. S. Bautista, K. Devi, and M. Ebrahim-Zadeh, “Yb-fiber-laser-based, 1.8 W average power, picosecond ultraviolet source at 266 nm,” Opt. Lett. 40(10), 2397–2400 (2015). [CrossRef]
20. C. Chang, P. Krogen, H. Liang, G. Stein, J. Moses, C. Lai, J. Siqueira, L. Zapata, F. Kärtner, and K. Hong, “Multi-mJ, kHz, ps deep-ultraviolet source,” Opt. Lett. 40(4), 665–668 (2015). [CrossRef]
21. S. C. Kumar, J. C. Casals, J. Wei, and M. Ebrahim-Zadeh, “High-power, high-repetition-rate performance characteristics of β-BaB2O4 for single-pass picosecond ultraviolet generation at 266 nm,” Opt. Express 23(21), 28091–28103 (2015). [CrossRef]
22. L. Goldberg, B. Cole, C. McIntosh, V. King, A. Hays, and S. Chinn, “Narrow-band 1 W source at 257 nm using frequency quadrupled passively Q-switched Yb:YAG laser,” Opt. Express 24(15), 17397–17405 (2016). [CrossRef]
23. M. Müller, A. Klenke, T. Gottschall, R. Klas, C. Rothhardt, S. Demmler, J. Rothhardt, J. Limpert, and A. Tünnermann, “High-average-power femtosecond laser at 258 nm,” Opt. Lett. 42(14), 2826–2829 (2017). [CrossRef]
24. K. Liu, H. Li, S. Qu, H. Liang, Q. J. Wang, and Y. Zhang, “20 W, 2 mJ, sub-ps, 258 nm all-solid-state deep-ultraviolet laser with up to 3 GW peak power,” Opt. Express 28(12), 18360–18367 (2020). [CrossRef]
25. T. Kojima, S. Konno, S. Fujikawa, K. Yasui, K. Yoshizawa, Y. Mori, T. Sasaki, M. Tanaka, and Y. Okada, “20-W ultraviolet-beam generation by fourth-harmonic generation of an all-solid-state laser,” Opt. Lett. 25(1), 58–60 (2000). [CrossRef]
26. B. Köhler, T. Andres, A. Nebel, and R. Wallenstein, “High-power, high-repetition-rate fourth and fifth harmonic generation of a cw mode locked Nd:YVO4 laser,” in Conference on Lasers and Electro-Optics, Technical Digest (Optica Publishing Group, 2000), paper CTuA8.
27. S. Konno, Y. Inoue, T. Kojima, S. Fujikawa, and K. Yasui, “Efficient high-pulse-energy green-beam generation by intracavity frequency doubling of a quasi-continuous-wave laser-diode-pumped Nd:YAG laser,” Appl. Opt. 40(24), 4341–4343 (2001). [CrossRef]
28. M. Nishioka, S. Fukumoto, F. Kawamura, M. Yoshimura, Y. Mori, and T. Sasaki, “Improvement of laser-induced damage tolerance in CsLiB6O10 for high-power UV laser source,” in Technical Digest of CLEO (2003), paper CTuF2.
29. G. Wang, A. Geng, Y. Bo, H. Li, Z. Sun, Y. Bi, D. Cui, Z. Xu, X. Yuan, X. Wang, G. Shen, and D. Shen, “28.4 W 266 nm ultraviolet-beam generation by fourth-harmonic generation of an all-solid-state laser,” Opt. Commun. 259(2), 820–822 (2006). [CrossRef]
30. A. Diening, S. McLean, and A. Starodoumov, “High average power 258 nm generation in a nanosecond fiber MOPA system,” Proc. SPIE 7195, 71950H (2009). [CrossRef]
31. Y. Orii, Y. Takushima, M. Yamagaki, A. Higashitani, S. Matsubara, S. Murayama, T. Manabe, I. Utsumi, D. Okuyama, and G. Okada, “High-energy 266-nm picosecond pulse generation from a narrow spectral bandwidth gain-switched LD MOPA,” in Tech. Digest of CLEO (2013), paper JTh2A.64.
32. O. Novák, H. Turčičová, M. Smrž, T. Miura, A. Endo, and T. Mocek, “Picosecond green and deep ultraviolet pulses generated by a high-power 100 kHz thin-disk laser,” Opt. Lett. 41(22), 5210–5213 (2016). [CrossRef]
33. H. Xuan, C. Qu, S. Ito, and Y. Kobayashi, “High-power and high-conversion efficiency deep ultraviolet (DUV) laser at 258 nm generation in the CsLiB6O10 (CLBO) crystal with a beam quality of M2<1.5,” Opt. Lett. 42(16), 3133–3136 (2017). [CrossRef]
34. H. Turcicova, O. Novak, L. Roskot, M. Smrz, J. Muzik, M. Chyla, A. Endo, and T. Mocek, “New observations on DUV radiation at 257 nm and 206 nm produced by a picosecond diode pumped thin-disk laser,” Opt. Express 27(17), 24286–24299 (2019). [CrossRef]
35. K. Kohno, Y. Orii, H. Sawada, D. Okuyama, K. Shibuya, S. Shimizu, M. Yoshimura, Y. Mori, J. Nishimae, and G. Okada, “High-power DUV picosecond pulse laser with a gain-switched-LD-seeded MOPA and large CLBO crystal,” Opt. Lett. 45(8), 2351–2354 (2020). [CrossRef]
36. Y. Orii, K. Kohno, H. Tanaka, M. Yoshimura, Y. Mori, J. Nishimae, and K. Shibuya, “Stable 10,000-hour operation of 20-W deep ultraviolet laser generation at 266 nm,” Opt. Express 30(7), 11797–11808 (2022). [CrossRef]
37. Y. Orii, K. Kohno, H. Tanaka, M. Yoshimura, Y. Mori, J. Nishimae, and K. Shibuya, “Minimization of the response time of a 20 W deep-ultraviolet light at 266 nm during intermittent operation,” Opt. Continuum 1(11), 2274–2286 (2022). [CrossRef]
38. L. Wang, N. Zhai, L. Liu, X. Wang, G. Wang, Y. Zhu, and C. Chen, “High-average-power 266 nm generation with a KBe2BO3F2 prism-coupled device,” Opt. Express 22(22), 27086–27093 (2014). [CrossRef]
39. D. Nikitin, O. Byalkovskiy, O. Vershinin, P. Puyu, and V. Tyrtyshnyy, “Sum frequency generation of UV laser radiation at 266 nm in LBO crystal,” Opt. Lett. 41(7), 1660–1663 (2016). [CrossRef]
40. N. Wang, J. Zhang, H. Yu, X. Lin, and G. Yang, “Sum-frequency generation of 133 mJ, 270 ps laser pulses at 266 nm in LBO crystals,” Opt. Express 30(4), 5700–5708 (2022). [CrossRef]
41. Y. H. Cha, S. Kim, and H. Park, “Generation of 12 W 257 nm laser pulses by sum-frequency generation based on LBO crystals,” Laser Phys. 32(8), 085002 (2022). [CrossRef]
42. Z. Hou, L. Liu, Z. Fang, L. Yang, D. Yan, X. Wang, D. Xu, and C. Chen, “High-power 266 nm laser generation with a NaSr3Be3B3O9F4 crystal,” Opt. Lett. 43(22), 5599–5602 (2018). [CrossRef]
43. W. L. Rong, W. G. Ling, Z. Xin, L. L. Juan, W. X. Yang, Z. Yong, and C. C. Tian, “Generation of Ultraviolet Radiation at 266 nm with RbBe2BO3F2 Crystal,” Chin. Phys. Lett. 29(6), 064203 (2012). [CrossRef]
44. Q. Liu, X. Yan, M. Gong, H. Liu, G. Zhang, and N. Ye, “High-power 266 nm ultraviolet generation in yttrium aluminum borate,” Opt. Lett. 36(14), 2653–2655 (2011). [CrossRef]
45. Z. Cui, M. Sun, D. Liu, and J. Zhu, “High-peak-power picosecond deep-UV laser sources,” Opt. Express 30(24), 43354–43370 (2022). [CrossRef]
46. L. J. Mawst, A. Bhattacharya, J. Lopez, D. Botez, D. Z. Garbuzov, L. DeMarco, J. C. Connolly, M. Jansen, F. Fang, and R. F. Nabiev, “8 W continuous wave front-facet power from broad-waveguide Al-free 980 nm diode lasers,” Appl. Phys. Lett. 69(11), 1532–1534 (1996). [CrossRef]
47. U. Brauch, C. Röcker, T. Graf, and M. A. Ahmed, “High-power, high-brightness solid-state laser architectures and their characteristics,” Appl. Phys. B 128(3), 58 (2022). [CrossRef]
48. D. Ouyang, Y. Chen, M. Liu, X. Wu, Q. Yang, F. Xu, M. Zhong, Q. Lue, and S. Ruan, “310 W picosecond laser based on Nd:YVO4 and Nd:YAG rod amplifiers,” Opt. Laser Technol. 148, 107668 (2022). [CrossRef]
49. Y. Sato, T. Taira, N. Pavel, and V. Lupei, “Laser operation with near quantum-defect slope efficiency in Nd:YVO4 under direct pumping into the emitting level,” Appl. Phys. Lett. 82(6), 844–846 (2003). [CrossRef]
50. X. Délen, F. Balembois, O. Musset, and P. Georges, “Characteristics of laser operation at 1064 nm in Nd:YVO4 under diode pumping at 808 and 914 nm,” J. Opt. Soc. Am. B 28(1), 52–57 (2011). [CrossRef]
51. Y. Bai, “Pumping wavelength related population inversion in Nd:doped laser,” AIP Adv. 10(10), 105309 (2020). [CrossRef]
52. K. Ganesan and N. Bidin, “Temperature dependence of 914 nm stimulated emission cross section of diode end-pumped nd:yvo4,” Buletin Optik 1(4), 1–5 (2016).
53. D. Sangla, F. Balembois, and P. Georges, “Nd:YAG laser diode-pumped directly into the emitting level at 938 nm,” in CLEO/Europe and EQEC 2009 Conference Digest (2009), paper CA12_4.
54. L. Chang, C. Yang, X. J. Yi, Q. K. Ai, L. Y. Chen, M. Chen, G. Li, J. H. Yang, and Y. F. Ma, “914 nm LD end-pumped 31.8 W high beam quality E-O Q-switched Nd:YVO4 laser without intracavity polarizer,” Laser Phys. 22(9), 1369–1372 (2012). [CrossRef]
55. D. Sangla, M. Castaing, F. Balembois, and P. Georges, “Highly efficient Nd:YVO4 laser by direct in-band diode pumping at 914 nm,” Opt. Lett. 34(14), 2159–2161 (2009). [CrossRef]
56. X. Ding, S. Yin, C. Shi, X. Li, B. Li, Q. Sheng, X. Yu, W. Wen, and J. Yao, “High efficiency 1342 nm Nd:YVO4 laser in-band pumped at 914 nm,” Opt. Express 19(15), 14315–14320 (2011). [CrossRef]
57. S. Goldring and R. Lavi, “Nd:YAG laser pumped at 946 nm,” Opt. Lett. 33(7), 669–671 (2008). [CrossRef]
58. Y. Lü, J. Zhang, J. Xia, and H. Liu, “Diode-Pumped Quasi-Three-Level Nd:YVO4 Laser With Orthogonally Polarized Emission,” IEEE Photonics Technol. Lett. 26(7), 656–659 (2014). [CrossRef]
59. F. Chen, J. Sun, R. Yan, and X. Yu, “Reabsorption cross section of Nd3+-doped quasi-three-level lasers,” Sci. Rep. 9(5620), 1–8 (2019).
60. S. Cante, S. J. Beecher, and J. I. Mackenzie, “Characterising energy transfer upconversion in Nd-doped vanadates at elevated temperatures,” Opt. Express 26(6), 6478–6489 (2018). [CrossRef]
61. R. Murai, T. Fukuhara, G. Ando, Y. Tanaka, Y. Takahashi, K. Matsumoto, H. Adachi, M. Maruyama, M. Imanishi, K. Kato, M. Nakajima, Y. Mori, and M. Yoshimura, “Growth of large and high quality CsLiB6O10 crystals from self-flux solutions for high resistance against UV laser-induced degradation,” Appl. Phys. Express 12(7), 075501 (2019). [CrossRef]
