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Abstract
We developed an optically synchronized highly stable frequency-doubled Nd:YAG laser with sub-nanosecond pulse duration. The 1064 nm seed pulses generated by soliton self-frequency shift in a photonic crystal fiber from Ti:sapphire oscillator pulses were stabilized by controlling input pulse polarization. The seed pulses were amplified to 200 mJ by diode-pumped amplifiers with a high stability of only <0.2% (rms). With an external LBO doubler, the system generated 330 ps green pulse energy of 130 mJ at 532 nm with a conversion efficiency of 65%. The pulse duration was further extended to 490 ps by adjusting Nd:YAG crystal temperature. To the best of our knowledge, these results present a longer pulse duration with higher stability than previous Nd:YAG lasers with sub-nanosecond optical synchronization.
© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Optical parametric chirped-pulse amplification (OPCPA) is a key technology for amplifying broadband pulses in high-intensity laser systems. The stability of the amplified pulses depends on the timing jitter between signal and pump pulses in the OPCPA because the gain strongly depends on the temporal overlapping of the two laser pulses. Typical timing jitter between a mode-locked oscillator and a Q-switched pump laser synchronized with a commercial delay generator is on the order of a nanosecond. The jitter could be reduced to ∼100 fs by electrical and optical phase feedback systems with two MHz mode-locked oscillators for signal and pump lasers [1,2]. Teisset et al. developed an optical synchronization scheme with a single oscillator by generating pump pulses from a portion of the signal pulses to reduce the timing jitter [3]. In their scheme, the spectrum of the signal pulse from the oscillator is expanded via soliton self-frequency shift (SSFS) by using a photonic crystal fiber (PCF) to generate a seed pulse of wavelength ∼1 µm. The seed pulses are amplified and then frequency-doubled for the OPCPA pump laser. A timing jitter less than 400 fs was achieved without any feedback system, and with feedback systems, the shortest timing jitter of 3 fs was reported [4–9]. Such capability with a single oscillator is essential and suitable for realizing a compact system.
OPCPA is also used in various Ti:sapphire-based petawatt laser systems as a pre-amplifier to obtain a broad spectrum and high-contrast laser pulses for subsequent Ti:sapphire amplifiers [10–14]. Integrating an optically synchronized pump laser into the ultra-high intensity laser system reduces timing jitter and thus provides a more stable laser output. Frequency-doubled Nd:YAG lasers are commonly used for the OPCPA pumping in the OPCPA/Ti:sapphire hybrid laser systems due to the efficient laser operation at room temperature without complex cooling systems. Optically synchronized Nd:YAG pump lasers using seed pulses generated from Ti:sapphire oscillator pulses have been developed by several research groups [3,15–20]. Herrmann et al. achieved the highest pulse energy of 1 J with an 80 ps pulse duration at 10 Hz at a wavelength of 532 nm [18]. Vaupel et al. achieved the longest pulse duration of 207 ps with 10 mJ pulse energy at 3 kHz at a wavelength of 532 nm [20]. These pulse durations are enough for the ps-order optically synchronized OPCPA in the first CPA stage as the HPLS 10 PW laser in the ELI-NP [13]. By contrast, the J-KAREN-P laser, developed at our institute, uses electrically synchronized OPCPA pumped by a frequency-doubled Nd:YAG laser as a pre-amplifier in the second CPA stage [14]. The broadband pulses in the second CPA stage are stretched to sub-nanosecond or more to avoid optical damage to the dielectric of bulk materials as well as self-focusing. A Nd:YAG laser with a long pulse duration and high pulse energy generated from Ti:sapphire oscillator femtosecond pulse is essential to introduce optically synchronized OPCPA in the second CPA stage without significant changes in the current configuration and optics. However, the narrow bandwidth of the Nd:YAG laser makes it challenging to stretch the pulse duration in sub-nanosecond or more after amplification due to the damage threshold and amount of dispersion.
In this paper, we report the development of a highly stable optically synchronized frequency-doubled Nd:YAG pump laser at an even longer pulse duration of 330 ps (FWHM) and a high pulse energy of 130 mJ at 10 Hz at a wavelength of 532 nm. A feedback control system stabilized a seed pulse wavelength of 1064 nm generated by the SSFS method with a PCF from a Ti:sapphire oscillator. The seed pulses were amplified in diode-pumped Yb:fiber amplifiers and Nd:YAG bulk amplifiers to 200 mJ at 10 Hz. These stable seed pulses allowed the achievement of an excellent energy stability of better than 0.2% (rms). An output pulse energy of 130 mJ at a wavelength of 532 nm was obtained with an external LBO doubler. The pulse duration was further extended to 490 ps (FWHM) by adjusting the Nd:YAG crystal temperature. This is the first demonstration of an Nd:YAG laser system with sub-nanosecond optical synchronization.
2. Laser system description
Figure 1 shows a schematic of the optically synchronized pump laser. All components were set on a water-cooled optical table (JVI Nippon Boushin Industry Co., Ltd., Numazu, Japan) to minimize temperature effects. The laser was composed of a Ti:sapphire oscillator, fiber systems for stable chirped-seed pulse generation at a wavelength of 1064 nm, bulk amplifier systems for high-energy amplification, and a frequency doubler.
Fig. 1. Schematic of optically synchronized pump laser for OPCPA. λ/2: half-wave plate; λ/4: quarter-wave plate; PCF: photonic crystal fiber; FBPF: fiber bandpass filter; FC: fiber circulator; CFBG: chirped fiber Bragg grating; PC: Pockels cell; FI: Faraday isolator; TFP: thin-film polarizer; AP: aperture; EXP: beam expander; SAP: serrated aperture; PBS: polarized beam splitter.
2.1 Stable seed pulse generation
A Ti:sapphire oscillator (Femtosource Rainbow, Femtolasers, Inc., Vienna, Austria) provided 7 fs pulses at a repetition rate of 80 MHz with a spectrum range of 650–1020 nm. The pulses were focused on a 23 cm PCF (NL-PM-750, NKT Photonics Inc., New Jersey, USA) to extend the spectrum range [21]. The input intensity was optimized by a feedback control system, which was composed of a spectrometer and a half-wave plate mounted on a motorized rotation stage, to stably obtain an output spectrum peak at 1064 nm. If the spectrum peak drifted with time, the 1064 nm pulse energy incident on the subsequent amplifier was reduced, causing the ultimate pulse energy after amplification to decrease. The primary contributions to wavelength variability arose from the spatial pointing fluctuation of the laser, from mechanical movements and variations of the optical components, and from air currents. The balance of coupling efficiency influenced by pointing and input pulse polarization to the PCF was tuned by adjusting the angle of the half-wave plate. Figure 2(a) shows the relation of the peak wavelength to the angle of the half-wave plate. The relation depended on laser intensity and on the optimal angle of the half-wave plate. Figure 2(b) shows the stability over time for the peak wavelength of the PCF output spectrum of approximately 1064 nm. The fluctuation of the peak wavelength was stabilized to 0.2 nm (0.02%, rms) over a period of 60 min using feedback control. Observed fluctuation involving peak wavelength shortening had almost no effect on downstream amplification. Hence, there is no need for further consideration of this shortening for our system. It is noted that the peak wavelength fluctuation at the PCF is independent of the timing jitter because pulses are not stretched by a pulse stretcher in this stage.
Fig. 2. (a) Measured relation of the peak wavelength to the angle of the half-wave plate. (b) Measured stability of peak wavelength of the PCF output spectrum of approximately 1064 nm under feedback control.
The stabilized pulses were amplified in stages by four Yb:fiber amplifiers. For efficient amplification without amplified spontaneous emission of approximately 1030 nm, fiber bandpass filters for 1064 nm with bandwidths of 10, 2, and 2 nm were inserted before the first, second, and fourth amplifiers, respectively. The pump power and the Yb:fiber length were adjusted to obtain high power output without nonlinear effects in the spectrum. After passing through the second fiber amplifier, the pulses were stretched to 1 ns by a chirped fiber Bragg grating (TeraXion Inc., Quebec, Canada), which was designed to output with group velocity dispersion of 5000 ps/nm at 0.2 nm bandwidth (FWHM) at a center wavelength of 1064.15 nm. The stretched pulses were amplified to 130 mW by the third and fourth fiber amplifiers with stability better than 0.2% (rms) over 3 h at 80 MHz.
2.2 High-energy amplification
The repetition rate of the output pulses from the fiber system was reduced from 80 MHz to 10 Hz by a Pockels cell (5046, FastPulse Technology, Inc., Saddle Brook, USA) to be amplified with a diode-pumped regenerative Nd:YAG amplifier and a two-pass Nd:YAG main amplifier [22,23] . Collimated Gaussian beam profile pulses with a diameter of 2.1 mm at 1/e2 were injected into the regenerative amplifier. The regenerative amplifier, with a cavity length of 2 m, was composed of a diode-pumped Nd:YAG amplifier head (Hamamatsu Photonics K.K., Hamamatsu, Japan), a concave mirror (f = 2.5 m), a convex mirror (f = −2 m), a Pockels cell (5046D, FastPulse Technology, Inc., Saddle Brook, USA), thin-film polarizers, an aperture of 2.5 mm diameter, and a half-wave plate. The regenerative amplifier was designed to keep a beam diameter of ∼2 mm on the rod to avoid Fresnel diffraction from the edge. The cavity was covered by vinyl sheets to avoid air fluctuation. The diameter and the length of the Nd:YAG rod were 6 and 95 mm, respectively. Three laser diode arrays, each capable of delivering 808 nm pulses with a peak power of 1.6 kW for pulse durations of 200 µs at 10 Hz, pumped the Nd:YAG rod in diffusive reflectors. Uniform pumping distribution through the cross-section of the Nd:YAG rod was produced by the amplifier head. The aperture of 2.5 mm diameter was inserted in front of the convex mirror to realize a good Gaussian output beam profile. Small signal gain per round trip was as high as ∼9. After 10 round trips, the pulses were amplified to ∼20 mJ with excellent energy stability of 0.3% (rms) over a period of 2 h. The amplified pulses, with a beam diameter of 2.3 mm, were expanded to a diameter of 4 mm at 1/e2 before passing through the two-pass main amplifier. The configuration of the main amplifier head was the same as that of the regenerative amplifier head, except that the number of laser diode arrays was 6, and the Nd:YAG rod had a diameter and length of 8 and 130 mm, respectively. A serrated aperture of 5 mm diameter was placed after the beam expander to avoid optical damage induced by Fresnel diffraction at the Nd:YAG rod. The beam image at the aperture was relayed by image relay telescope to the LBO crystal, maintaining a spatially uniform beam profile during two-pass amplification in the main amplifier. A pulse energy of over 200 mJ was achieved with excellent stability of better than 0.2% (rms) over a period of 120 min in the main amplifier (Fig. 3). The fundamental beam profile at the LBO crystal is shown as an inset in Fig. 3(b). The triangle shape surrounding the profile represents the shadow of the serrated aperture. The increased temperature of the Nd:YAG rod under maximum pumping conditions was calculated to be less than 19.5°C by using a finite-element code LASCAD [24]. The increase of rod temperature was negligible small, therefore the thermal depolarization was negligible at the main amplifier. The B-integral values at the regenerative amplifier and main amplifier were estimated to be 5.54 and 3.27, respectively.
Fig. 3. Measured pulse energy after passing through the two-pass main amplifier. (a) Dependence of output energy from the main amplifier on input pulse energy. (b) Fluctuation of a pulse energy of over 200 mJ with a stability better than 0.2% (rms) over a period of 120 min. Inset shows the fundamental beam profile before passing through the LBO crystal.
2.3 Frequency doubling and pulse duration measurement
The amplified pulses were frequency-doubled in the LBO crystal with a cross-section of 10 mm square and a length of 13 mm. The crystal had anti-reflection coating and was oriented for Type-I SHG of the 1064-nm input fundamental laser. The length was optimized using a numerical model based on the coupled wave equations for our system. The crystal was housed in a heater to constantly maintain at 23 °C. Figure 4 shows the dependence of the output SHG energy on the input fundamental energy and fluctuation of the SHG pulse energy. A pulse energy of 130 mJ with a stability of 0.6% (rms) at a wavelength of 532 nm was obtained with a conversion efficiency of 64%. The second-harmonics profile is shown as an inset in Fig. 4. The second harmonic and fundamental pulse durations were measured with a 30 GHz oscilloscope (10-30Zi-A, Teledyne LeCroy, Inc., Chestnut Ridge, USA) and a biplanar phototube (R1328U-51, Hamamatsu Photonics K.K., Hamamatsu, Japan) (Fig. 5). The initial pulse duration of the input pulse to the regenerative amplifier was ∼1 ns (FWHM), which agrees with the specification of the chirped fiber Bragg grating. However, the pulse duration became shorter as the number of round trips in the regenerative amplifier increased. The pulse duration after regenerative amplification and frequency doubling were 360 and 330 ps (FWHM), respectively.
Fig. 4. Measured pulse energy after frequency doubling by LBO crystal. (a) Dependence of SHG energy on input fundamental energy. (b) Fluctuation of an SHG pulse energy of over 130 mJ with a stability of 0.6% (rms) over a period of 120 min. Inset shows the beam profile of frequency-doubled pulse after passing through the LBO crystal.
Fig. 5. Measured pulse shapes before passing through the regenerative amplifier (gray), after five round trips (blue), after 10 round trips (red), all of which are outputs of regenerative amplifier, and after frequency doubling (green).
3. Control toward longer pulse generation
We investigated the phenomenon of pulse shortening due to the pulse shape distortion behavior of high-gain chirped-pulse amplification in the regenerative amplifier. If the amplified pulse shapes are calculated from the input pulse by using the Frantz–Nodvik equation [25] with a constant value of stimulated emission cross-section over the wavelength, the pulse duration is more than 850 ps. The wavelength dependence of the stimulated emission cross-section is considered in the following calculations [26]. In the experiment the Nd:YAG rod in the regenerative amplifier head was cooled by water of 18°C. The maximum temperature of the Nd:YAG rod under pumping conditions was calculated to be 18.5°C by using a finite-element code LASCAD. Assuming a rod temperature of 18.5°C and a spectrum of 1064.143 ± 0.11 nm (FWHM) for the chirped input pulse, in reference to the specification of the fiber Bragg grating, the pulse shortening of the amplified pulse shape is well reproduced as shown in Fig. 6. Dashed line in Fig. 6 shows a calculated pulse shape after 10 round trips at a rod temperature of 31.5°C. The pulse duration was increased to 620 ps because the wavelength of the peak cross-section shifts to a longer wavelength when the rod temperature increases. This shift corresponds to a shift of the peak to the later side of the chirped-pulse shape. To confirm this effect experimentally, we measured the amplification at a 31°C cooling water temperature (Fig. 7). The pulse duration after passing through the regenerative amplifier was able to be extended to 600 ps, in good agreement with the calculation results. After passing through the main amplifier, the pulse duration was shortened to 540 ps. Therefore, we consider the pulse shortening to be due to gain narrowing caused by the decrease in stored energy when the latter part of the pulse is amplified. The pulse duration after doubling was 490 ps. Higher group velocity dispersion and a lower-bandwidth fiber Bragg grating are required for longer pulse generation. The increase in the chirp rate of the incident pulse makes it possible for the regenerative amplifier to generate a longer pulse.
Fig. 6. Measured (solid lines) and calculated (dotted lines) pulse shapes after five round trips (blue) and after 10 round trips (red) at the regenerative amplifier at a rod temperature of 18.5°C. Dashed line shows the calculated pulse shape after 10 round trips at a rod temperature of 31.5°C.
Fig. 7. Measured pulse shapes before passing through the regenerative amplifier (gray), after passing through the regenerative amplifier (red), after passing through the main amplifier (pink), and after frequency doubling (green).
4. Summary
We successfully demonstrated a highly stable optically synchronized green pump laser with the longest pulse duration yet reported at a wavelength of 532 nm. The PCF output at a wavelength of 1064 nm was stabilized to 0.2 nm (rms: 0.02%) over a period of 2 h by using a feedback control system built in-house. LD-pumped Yb:fiber amplifiers and Nd:YAG amplifiers amplified the stabilized pulses to 200 mJ with excellent energy stability of better than 0.2% (rms) over a period of 2 h at 10 Hz. A good beam profile was obtained by passing the beam through an aperture in regenerative amplifier and a serrated aperture prior to the main amplifier. A pulse energy of 130 mJ (rms: 0.6%) with a pulse duration of 330 ps at a wavelength of 532 nm was obtained using frequency doubling by the LBO crystal. The optimization of Nd:YAG crystal temperature allowed longer pulse durations of 600 and 490 ps to be obtained at wavelengths 1064 and 532 nm, respectively. This system is currently being applied to pump ultrafast OPCPA in a petawatt-class laser system.
Funding
Council for Science, Technology and Innovation (ImPACT Program); Japan Society for the Promotion of Science (JSPS) KAKENHI (JP16K17541).
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. R. T. Zinkstok, S. Witte, W. Hogervorst, and K. S. E. Eikema, “High-power parametric amplification of 11.8-fs laser pulses with carrier-envelope phase control,” Opt. Lett. 30(1), 78–80 (2005). [CrossRef]
2. H. Fattahi, C. Y. Teisset, O. Pronin, A. Sugita, R. Graf, V. Pervak, X. Gu, T. Metzger, Z. Major, F. Krausz, and A. Apolonski, “Pump-seed synchronization for MHz repetition rate, high-power optical parametric chirped pulse amplification,” Opt. Express 20(9), 9833–9840 (2012). [CrossRef]
3. C. Y. Teisset, N. Ishii, T. Fuji, T. Metzger, S. Köhler, R. Holzwarth, A. Baltuška, A. M. Zheltikov, and F. Krausz, “Soliton-based pump-seed synchronization for few-cycle OPCPA,” Opt. Express 13(17), 6550–6557 (2005). [CrossRef]
4. S. Klingebiel, I. Ahmad, C. Wandt, C. Skrobol, S. A. Trushin, Z. Major, F. Krausz, and S. Karsch, “Experimental and theoretical incestigation of timing jitter inside a stretcher-compressor setup,” Opt. Express 20(4), 3443–3455 (2012). [CrossRef]
5. I. Ahmad, S. A. Trushin, Z. Major, C. Wandt, S. Klingebiel, T. J. Wang, V. Pervak, A. Popp, M. Siebold, F. Krausz, and S. Karsch, “Frontend light source for short-pulse pumped OPCPA system,” Appl. Phys. B 97(3), 529–536 (2009). [CrossRef]
6. A. Schwarz, M. Ueffing, Y. Deng, X. Gu, H. Fattahi, T. Metzger, M. Ossiander, F. Krausz, and R. Kienberger, “Active stabilization for optically synchronized optical parametric chirped pulse amplification,” Opt. Express 20(5), 5557–5565 (2012). [CrossRef]
7. R. Riedl, M. Schulz, M. J. Prandolini, A. Hage, H. Höppner, T. Gottschall, J. Limpert, M. Drescher, and F. Tavella, “Long-term stabilization of high power optical parametric chirped-pulse amplifiers,” Opt. Express 21(23), 28987–28999 (2013). [CrossRef]
8. S. Prinz, M. Häfner, M. Schultze, C. Y. Teisset, R. Bessing, K. Michel, R. Kienberger, and T. Metzger, “Active pump-seed-pulse synchronization for OPCPA with sub-2-fs residual timing jitter: erratum,” Opt. Express 26(5), 5512–5513 (2018). [CrossRef]
9. A. Vaupel, N. Bodnar, B. Webb, L. Shah, and M. Richardson, “Concepts, performance review, and prospects of table-top, few-cycle optical parametric chirped-pulse amplification,” Opt. Eng. 53(5), 051507 (2013). [CrossRef]
10. H. Kiriyama, M. Mori, Y. Nakai, T. Shimomura, M. Tanoue, A. Akutsu, S. Kondo, S. Kanazawa, H. Okada, T. Motomura, H. Daido, T. Kimura, and T. Tajima, “High-contrast, high-intensity laser pulse generation using a nonlinear preamplifier in a Ti:sapphire laser system,” Opt. Lett. 33(7), 645–647 (2008). [CrossRef]
11. D. N. Papadopoulous, J. P. Zou, C. L. Blanc, G. Chériaux, P. Georegs, F. Druon, G. Mennerat, P. Ramirez, L. Martin, A. Fréneaux, A. Bluze, N. Lebas, P. Monot, F. Mathieu, and P. Audebert, “The Apollon 10 PW laser: experimental and theoretical investigation of the temporal characteristics,” High Power Laser Sci. Eng. 4, e34 (2016). [CrossRef]
12. H. W. Lee, Y. G. Kim, J. Y. Yoo, J. W. Yoon, J. M. Yang, H. Lim, C. H. Nam, J. H. Sung, and S. K. Lee, “Spectral shaping of an OPCPA preamplifier for a sub-20-fs multi-PW laser,” Opt. Express 26(19), 24775–24783 (2018). [CrossRef]
13. S. Gales, K. A. Tanaka, D. L. Balabanski, F. Negoita, D. Stutman, O. Tesileanu, C. A. Ur, D. Ursescu, I. Andrei, S. Ataman, M. O. Cernaianu, L. D’Alessi, I. Dancus, B. Diaconescu, N. Djourelov, D. Filipescu, P. Ghenuche, D. G. Ghita, C. Matei, K. Seto, M. Zeng, and N. V. Zamfir, “The extreme light infrastructure—nuclear physics (ELI-NP) facility: new horizons in physics with 10 PW ultra-intense lasers and 20 MeV brilliant gamma beams,” Rep. Prog. Phys. 81(9), 094301 (2018). [CrossRef]
14. H. Kiriyama, A. S. Pirozhkov, M. Nishiuchi, Y. Fukuda, K. Ogura, A. Sagisaka, Y. Miyasaka, M. Mori, H. Sakaki, N. P. Dover, K. Kondo, J. K. Koga, T. Z. Esirkepov, M. Kando, and K. Kondo, “High-contrast high-intensity repetitive petawatt laser,” Opt. Lett. 43(11), 2595–2598 (2018). [CrossRef]
15. O. D. Mücke, D. Sidorov, P. Dombi, A. Pugžlys, S. Ališauskas, V. Smilgevičius, N. Forget, J. Posius, L. Giniūnas, R. Danielius, and A. Baltuška, “10-mJ optically synchronized CEP-stable chirped parametric amplifier at 1.5 µm,” Opt. Spectrosc. 108(3), 456–462 (2010). [CrossRef]
16. G. Andriukaitis, T. Balčiūnas, S. Ališauskas, A. Pugžlys, A. Baltuška, T. Popmintchev, M.-C. Chen, M. M. Murnane, and H. C. Kapteyn, “90 GW peak power few-cycle mid-infrared pulses from an optical parametric amplifier,” Opt. Lett. 36(15), 2755 (2011). [CrossRef]
17. F. Tavella, A. Marcinkevlčius, and F. Krausz, “Investigation of the superfluorescence and signal amplification in an ultrabroadband multiterawatt optical parametric chirped pulse amplifier system,” New J. Phys. 8(10), 219 (2006). [CrossRef]
18. D. Herrmann, L. Veisz, R. Tautz, F. Tavella, K. Schmid, V. Pervak, and F. Krausz, “Generation of sub-three-cycle, 16TW light pulses by using noncollinear optical parametric chirped-pulse amplification,” Opt. Lett. 34(16), 2459–2461 (2009). [CrossRef]
19. W. He-Lin, Y. Ai-Jim, L. Yu-Xin, W. Cheng, X. Zhi-Zhan, and H. Lan-Tian, “Optical parametric chirped pulse amplification based on photonic crystal fiber,” Chin. Phys. B 20(8), 084208 (2011). [CrossRef]
20. A. Vaupel, N. Bodnar, B. Webb, L. Shah, M. Hemmer, E. Cormier, and M. Richardson, “Hybrid master oscillator power amplifier system providing 10 mJ, 32 W, and 50 MW pulses for optical parametric chirped-pulse amplification pumping,” J. Opt. Soc. Am. B 30(12), 3278–3283 (2013). [CrossRef]
21. N. Ishii, C. Y. Teisset, S. Köhler, E. E. Serebryannikov, T. Fuji, T. Metzger, F. Krausz, A. Baltuška, and A. M. Zheltikov, “Widely tunable soliton frequency shifting of few-cycle laser pulses,” Phys. Rev. E 74(3), 036617 (2006). [CrossRef]
22. M. Saeed, D. Kim, and L. F. DiMauro, “Optimization and characterization of a high repetition rate, high intensity Nd:YLF regenerative amplifier,” Appl. Opt. 30(18), 2527–2532 (1991). [CrossRef]
23. C. G. Durfee and H. M. Milchberg, “Pulse compression in a self-filtering Nd:YAG regenerative amplifier,” Opt. Lett. 17(1), 37–39 (1992). [CrossRef]
24. LAS-CAD GmbH. Available online: http://www.las-cad.com/ (accessed on 1 February 2021).
25. L. M. Frantz and J. S. Nodvik, “Theory of Pulse Propagation in a Laser Amplifier,” J. Appl. Phys. 34(8), 2346–2349 (1963). [CrossRef]
26. Y. Sato and T. Taira, “Temperature dependencies of stimulated emission cross section for Nd-doped solid-state laser materials,” Opt. Mater. Express 2(8), 1076 (2012). [CrossRef]
