用于汤姆孙散射诊断的高重频高光束质量焦耳级Nd：YAG纳秒激光器∗

摘要

A joule-level Nd:YAG nanosecond laser of high repetition frequency and high beam quality is developed for Thom-son scattering diagnosis. The laser is designed as a master oscillator power-amplifier system mainly including single longitudinal mode seed, pre-amplifier unit and energy extraction unit. The single-longitudinal-mode Q-switched laser of a high stability is taken as the seed laser of output pulse at µJ level. The pre-amplifier unit amplifies the µJ-level pulse laser beam into hundreds of mJ level. In order to obtain the high-quality laser beam output, phase conjugation is adopted to compensate for the laser beam distortion. The ultra-filtered FC-770 is taken as an SBS gain medium of 0.0011 cm−1 absorption coefficient, 197.9 GW/cm2 optical breakdown threshold and 3.5 cm/GW gain coefficient. The double-pass amplification of SBS phase conjugation could realize a real-time repair towards the non-uniformity, deformation and wavefront aberration caused by thermal distortion of the optical components and the laser amplifier to achieve the uniform amplified beam output of high quality close to the diffraction limit. In the energy extraction unit, the amplifier of large-diameter slab is used for energy amplification. The size of the slab is 7 mm × 35 mm × 138.2 mm of 56◦ cutting angle and 0.6% Nd3+ doping concentration. The slab is plated by a layer of SiO2 against light leak. Horizontal pumping mode is adopted. And the slow axis of the laser diode is almost the same as the length of the slat and the direction of laser transmission. The single-plane array is composed of 8 groups of vertical stacks and each group consists of 12 laser diode bars of power 200 W. At 200 Hz repetition frequency, 250 µs pump pulse width and 140 A pump current, the up to 2.3 J stored energy can be achieved The energy extraction unit achieves high gain amplification and finally outputs high-quality laser beam. Under the condition of 200 Hz high repetition frequency and 8.23 µJ single pulse energy injected by the single longitudinal mode seed, 1.85 J output energy is gained. The energy extract efficiency of the laser system is 52.46%. The output laser possesses a pulse width of 5.36 ns, a far field beam spot 1.72 times the diffraction-limited value, and 1.3%energy stability (RMS).%基于激光二极管抽运棒状放大器和板条放大器相结合的方式,研制了一台应用于汤姆孙散射诊断的高重复频率、高光束质量焦耳级的Nd：YAG纳秒激光器.激光器采用主振荡功率放大的结构,主要包括单纵模种子、预放大单元和能量提取单元三部分.为了获得高光束质量的激光输出,采用相位共轭技术对激光光束畸变进行补偿.在重复频率200 Hz、单纵模种子注入单脉冲能量8.23µJ的条件下,获得了1.85 J的能量输出.输出激光的脉冲宽度为5.36 ns,远场光斑为1.72倍衍射极限,能量稳定性(RMS)为1.3%.