| High pulse energy and high-average-power picosecond lasers are widely used in space debris ranging,fine processing,medical applications,and scientific research.However,the damage of optical components caused by non-linear effects such as selffocusing due to high pulse peak intensity during the power amplification process,as well as beam depolarization caused by thermally induced birefringence in the gain module,making it difficult to obtain high energy,high average power,and better beam quality picosecond lasers.Besides,for short pulses,the energy extraction efficiency is very low,which also increases the difficulty of the system.Therefore,the development of high single pulse energy and high-average-power picosecond lasers that can operate safely and stably for a long time has important research significance and engineering practical value.Based on theoretical analysis and numerical simulation,the SESAM(semiconductor saturable absorption mirror)passive mode-locking is used to generate picosecond ultra-short pulse seed light,and the burst-mode pulses obtained by the pulse stretcher and beam splitter is injected into the regenerative amplifier(RA)for high-gain amplification,followed by beam shaping,two-stage traveling-wave amplification,and frequency doubling.Finally,a high-average-power burst-mode picosecond green laser is obtained.The content of the thesis is mainly divided into the following parts.1.The research background of high-power picosecond lasers is introduced,and its application value is described in the term of space debris laser ranging.Various technologies and methods developed for obtaining high pulse energy and high average power picosecond laser light sources are summarized.It also summarizes the development status of the research on regeneration amplification theory,and finally introduces the main research content of this article.2.The mechanism of picosecond pulse generation,the principle of regenerative amplification,and the frequency doubling theory of passive mode-locking of SESAM was analyzed and explained,which laid a theoretical foundation for subsequent experimental research.3.Based on the ABCD matrix method,a mode-locked cavity with adjustable coupling output rate of cavity mirror is designed.According to the passive mode-locking theory of SESAM,the influence of the coupling output rate of cavity mirror on the mode locking state,beam quality and output power of the beam is studied..4.The evolution model of the brust-mode pulses in the regenerative amplification cavity is established,by extending the existing single-pulse regenerative amplification theory.The effects of seed pulses energy and energy distribution on the overall extraction energy and energy distribution of the brust-mode RA output beam are mainly considered.The effect of the number of injection pulses on the pointing stability of the regenerative amplified output beam is experimentally studied.By increasing the number of injection pulses and cavity optimization,the regenerative amplified light with a beam pointing stability better than ± 8.75 ?Rad is finally obtained,and the jitter is relatively uniform in all directions in space.A traveling wave amplification experiment is performed,and a 1064 nm laser with an output power of 100 W was obtained.5.Based on the finite element method,the internal temperature field distribution of the frequency-doubling crystal in different states is theoretically simulated,and it is used to improve and optimize the frequency-doubling scheme.A high-power picosecond laser extra-cavity frequency doubling experiment is carried out to study the effect of different frequency doubling schemes on the second harmonic conversion efficiency and the effect of the number of pulses on frequency doubling efficiency under the same burst-mode fundamental frequency optical pumping.By adding multiple 4F aerial image transmission systems to improve beam quality and adding polarizers to improve the polarization purity of the fundamental frequency beam,green light with a power greater than 50 W was finally obtained,which corresponds to the second harmonic conversion efficiency reaches 68%.The beam quality factor M2 is less than 3.4,and the long-term power stability is better than 1%. |
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