Studies on compact high-power all-solid-state picosecond oscillators and amplifiers

小型化高功率全固态皮秒激光器和放大器在科研、军事、医药和激光微纳加工等领域有着广泛和重要的应用，如非线性频率转换、生物光子学、激光测距和激光微纳加工等。由于商业半导体激光器的迅速发展以及在放大过程中不需要使用啁啾脉冲放大技术，皮秒激光器具有效率高，成本低，体积小，稳定性好等优点。和钛宝石飞秒激光器相比，皮秒激光器在工业应用环境以其低成本和高重复频率显示了独特的优势。今天，发展高功率，高重复频率，高光束质量的小型化全固态皮秒激光器具有重大的科学意义和应用价值。 目前，Nd:YVO4和Nd:YAG激光晶体以其优良的光学性能和机械性能以及可利用半导体激光器直接进行泵浦等优点，在全固态激光领域被广泛地研究和应用。为了研发出性能稳定的，高功率，高光束质量的Nd类超快激光器以满足各种应用的需求，本论文开展了基于Nd:YVO4和Nd:YAG的高重复频率，高功率皮秒激光系统的相关技术研究。主要的创新成果概括如下： 1、半导体激光泵浦Nd:YVO4晶体脉宽可调谐高功率锁模激光器研究。 采用半导体激光器泵浦，对Nd:YVO4晶体进行了连续及锁模激光实验研究。当晶体吸收泵浦功率为14.25 W时，得到了功率6.8 W，中心波长1064 nm的激光输出，对应的光光转换效率47.7%。利用SESAM作为锁模器件，实现了最高平均功率5 W的锁模激光输出，脉冲宽度为7 ps。该输出结果在国际同类激光器中处于领先水平。 设计了双端双泵、双晶体结构的被动锁模激光器，利用在激光腔不同位置插入两块Nd:YVO4晶体，通过控制其泵浦比例，实现了8.8 ps~20.3 ps的脉冲宽度可调谐输出。该结果为已知报道中首例基于Nd:YVO4晶体采用该类结构的脉宽可调谐锁模激光振荡器。 2、基于侧面连续泵浦Nd:YAG晶体的高功率再生放大器实验研究。 利用侧面连续泵浦Nd:YAG晶体作为再生放大介质，设计了高平均功率的再生放大器，实现了最高功率为8.8 W，重复频率为5 kHz，脉宽为28 ps的1064 nm再生放大输出。对应单脉冲能量1.76 mJ，峰值功率63 MW。该结果为已知报道基于侧面连续泵浦Nd:YAG晶体皮秒激光再生放大器中，获得的最大单脉冲能量。 3、基于Nd:YVO4片状晶体的带内泵浦Innoslab振荡放大器实验研究。 利用片状Nd:YVO4晶体为增益介质，研究了Innoslab带内泵浦、振荡放大器。在实验中创新发展了Innoslab放大器的模式匹配方式，充分结合了带内泵浦和Innoslab放大器二者的优势，最终实现了平均功率105 W，脉冲宽度为8.4 ps，重复频率120 MHz的皮秒激光放大输出。该结果为已知报道中，基于Nd:YVO4晶体Innoslab放大器设计获得的最高平均功率。Compact, high-power, all-solid-state picosecnond oscillators and amplifiers have significant applications in scientific research, military, medicine and industrial processing, including efficient frequency conversion, biological microscopy, laser ranging and laser micro-nano fabrication. Given the commercial development of laser diodes and non-requirement of chirped-pulse amplification, current picosecond lasers are highly efficient, low cost, small scale and reliable. Compared with Ti:sapphire lasers, picosecond lasers are well adapted to the industrial environment, which have a much more lower cost and higher repetition rate. Presently, compact all-solid-state picosecond lasers with high average power and high repetition rates, combined with near-diffraction limited beam quality, are highly needed in scientific research fields and other applications. With capacity for conveniently pumping with laser diodes and excellent optical and mechanical properties, Nd:YVO4 and Nd:YAG have been the most extensively studied and widely used in all-solid-state lasers. In order to develop reliable all-solid-state neodymium-doped ultrafast lasers with high average power and high beam quality for different applifcations, systematic experimental laser studies have been carried out in this dissertation. The main results in this dissertation have been summarized as follows: 1. Experimental research on diodes-pumped high power pulsewidth tunable mode-locked Nd:YVO4 lasers. With diodes as pump sources, continuous-wave laser performance of Nd:YVO4 was investigated. At an absorbed pump power of 14.25 W at 808 nm, the maximum output power of 6.8 W at 1064 nm was obtained, corresponding to a laser slope efficiency of 47.7%. With a SESAM adopted in the cavity, a maximum average power of 5 W was achieved. The pulse duration was measured to be 7 ps. The results reached the advanced level of our knowledgment. A passively mode-locked Nd:YVO4 laser with two gain medium at different locations in the cavity was designed. By manipulating the pump ratio of the two crystals, laser output with pulse width of 8.8 ps ~20.3 ps was achieved. To the best of our knowledge, this is the first pulse width tunable mode-modelocked Nd:YVO4 laser based on this design. 2. Experimental research on high power picosecond regenerative amplifier based on CW diode side-pumped Nd:YAG crystal. A compact high power picosecond regenerative amplifier based on cw-diode side-pumped Nd:YAG was designed. Average power of 8.8 W was demonstrated at a repetition rate of 5 kHz at the wavelength of 1.064 m with a pulse duration of 28 ps, corresponding to a pulse energy of 1.76 mJ and a peak power of 62.9 MW. The beam quality is close to the diffraction limit with M2x = 1.24, M2y = 1.03. To the best of our knowledge, This is the highest pulse energy from a cw-diodes side-pumped Nd:YAG picosecond regenerative amplifier. 3. Experimental research on in-band pumped Nd:YVO4 Innoslab master oscillator power amplifier. We investigated on a compact and effcient in-band pumped Nd:YVO4 Innoslab picosecond amplifier. A new method for mode matching was demonstrated to simplify the amplifier design. Integrating the benefits of the in-band pumping technique and the excellent thermal management of the Innoslab amplifier design, a 105 W, 8.4 ps, 120 MHz laser output was achieved with near-diffraction limited beam quality of M2x = 1.12 and M2y = 1.09 in the orthogonal directions. To the best of our knowledge, this is the highest picosecond output power based on a Nd:YVO4 Innoslab amplifier