High beam quality 5 J, 200 Hz Nd:YAG laser system

Abstract

A high beam quality, all-solid-state Nd:YAG laser system of high-repetition frequency has been built for Thomson scattering diagnosis. A 1.7 times diffraction limited output beam at a pulse energy of 5 J at 1064 nm is achieved for the first time with a pulse duration of 6.6 ns (FWHM) and a repetition rate of 200 Hz; the output energy stability is 4.9% peak-to-valley over 6000 shots.A novel pulsed laser system (Supplementary Fig. S1) with high average power and high beam quality has recently been built by Dr Zhong-Wei Fan's group at the Academy of Opto-Electronics, Chinese Academy of Sciences. Both the laser diode side-pumped rod and slab crystals are integrated into the amplifier (AMP) system. A 1.7 times diffraction-limited output beam at a pulse energy of 5 J at 1064 nm is achieved for the first time with a pulse duration of 6.6 ns (FWHM) and a repetition rate of 200 Hz; the output energy stability is 4.9% peak-to-valley over 6000 shots. The test results are shown in Figure 1a and 1b.The laser system is constructed in a master oscillator power amplifier (MOPA) configuration, as shown in Figure 1c, with four components: a single-frequency seed laser, pre-amplifier unit, beam control unit, and post-amplifier unit. The pre-amplifier consists of a three-stage, side-pumped rod amplifier. The dimensions of the rod crystals are φ3 mm × 67 mm with a Nd 3+ concentration of 0.8% for AMP1 and AMP2, and φ6.35 mm × 140 mm with a Nd 3+ concentration of 0.6% for AMP3 and AMP4. The techniques of the stimulated Brillouin scattering phase-conjugate mirror (SBS-PCM) and adaptive optics are implemented in the beam control unit to correct the wavefront distortion dynamically. The postamplifier unit is composed of a three-stage, large slab amplifier. The dimensions of the slab crystals are 138 mm (L) × 35 mm (W) × 7 mm (D) with a Nd 3+ concentration of 0.6% for AMP5, AMP6 and AMP7. The single-frequency seed laser produces an output power of 8.58 μJ with a pulse duration of 33.9 ns (FWHM) at a 200-Hz repetition rate. The root-mean-square (RMS) fluctuation in pulse energy is smaller than 1% and the beam quality is better than 1.12 times diffraction limited. The seed pulses first pass through the pre-amplifier and then through the control unit, at which the beam shaping is applied. The pulse energy is amplified to 300 mJ. The pulse duration is 30.5 ns and the beam quality is better than 1.4 times diffraction-limited. After passing through the post-amplifier, the pulse energy reaches 5 J with 3.2 times diffraction limited beam quality. An adaptive optics system is applied for wavefront correction, and the beam quality is improved to 1.7 times diffraction limited.The core parts of the laser system include the single-frequency laser source, slab amplifier module with high-energy storage efficiency, and the phase-conjugated, stimulated Brillouin scattering mirror. The single-frequency source is an active Q-switching laser utilizing acousto-optic modulation. Single-longitudinalmode operation is achieved by applying a Fabry-Pérot (FP) etalo...

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High‐Power Laser Systems

“…In addition to the above conventional adjustments, people have also developed some targeted design Raman filter fibers for the Sub -GW Rod-type 0.69 GW 9 J 13 ns 10 Hz 2017 [86] Zigzag slab 0.76 GW 5 J 6.6 ns 200 Hz 2017 [72] Active mirror slab 1.74 GW 13.9 J 8 ns 2 Hz 2013 [89] 0.85 GW 8.5 J 10 ns 1 Hz 2014 [ 196] 0.1 GW 1 J 10 ns 100 Hz 2015 [ 197] 1.22 GW 12.2 J 10 ns 10 Hz 2017 [90] 1.28 GW 12 J 9.4 ns 10 Hz 2019 [83] 1.03 GW 10.3 J 10 ns 10 Hz 2019 [48] 0.93 GW 9.3 J 10 ns 33.3 Hz 2021 [49] Thin-disk multipass 0.18 GW b)…”

“…[71] However, even if the most advanced thermal managements are used, it is difficult to completely eliminate the wavefront distortion in the high-intensity amplification process. [72,73] The laser wavefront distortion caused by the thermal effect of the amplifier can be compensated to improve the laser beam quality by using phase conjugate mirror or adaptive optics. [74,75] A beam spot energy distribution before and after correction is illustrated in Figure 1g.…”

“…At present, it is mainly used in highenergy pulsed lasers pumped by flash lamps [82] and the preamplification stage of high-energy ns/ps lasers. [72,[83][84][85] There are also examples where high-energy pulsed lasers are directly realized by diode laser pumped rod lasers. Xu et al reported that PDLpumped Nd:YLF rods achieved an output of 9 J, 13 ns, 10 Hz, and 1053 nm, corresponding to a peak power of 692.3 MW.…”

“…Fan et al used three-stage series zigzag Nd:YAG amplifiers and reported an output of 5 J, 6.6 ns, 200 Hz, and 1064 nm, corresponding to a peak power of 757.6 MW. [72] The seed beam propagates down the slab by multiple total internal reflections, forming an unextracted energy storage area and reducing the amplification efficiency. [87] Temperature gradients limit power scaling in the gain medium before the medium is damaged.…”