【作者】 马宁；

【导师】 陈檬；

【作者基本信息】 北京工业大学 ， 光学工程（专业学位）， 2020， 硕士

【摘要】 高脉冲能量、高平均功率皮秒激光广泛应用于空间碎片测距、精细加工、医疗应用以及科学研究等领域。然而,皮秒激光因其较窄的脉宽在功率放大过程中极易因峰值功率过高引起自聚焦等非线性效应造成光学元器件的损伤,以及增益模块因热致双折射所引起的光束退偏等因素,导致难以获得高能、高平均功率和较好光束质量的皮秒激光光源。此外,对于短脉冲,激光能量提取效率非常低,增加了系统研制困难。因此,研制可长期安全稳定运行的高单脉冲能量、高平均功率皮秒激光器具有重要的研究意义和工程实用价值。本论文在理论分析与数值模拟的基础上,采用SESAM(半导体可饱和吸收镜)被动锁模技术产生皮秒超短脉冲种子光,经脉冲展宽器、光束分束器获得脉冲串激光注入到再生放大器中进行高增益放大,再依次经过光束整形、两级行波放大以及倍频,最终获得高功率皮秒脉冲串绿光激光光源。论文内容主要分为以下几个部分。1、介绍了高功率皮秒激光器的研究背景并从空间碎片激光测距方面阐述了它的应用价值,总结了为获得高脉冲能量和高平均功率的皮秒激光光源所发展的各种技术和方法,并对再生放大理论研究的发展现状进行了梳理,最后介绍了本文主要研究内容。2、对SESAM被动锁模产生超短脉冲机理、再生放大原理和倍频理论进行了分析与阐述,为后续实验研究奠定了理论基础。3、基于ABCD矩阵法,设计了腔镜耦合输出率可调节的锁模振荡腔;依据SESAM被动锁模理论,研究了腔镜耦合输出率对光束的锁模状态、光束质量和输出功率等性质的影响。4、对现有的单脉冲再生放大理论进行扩展,获得脉冲串在再生放大腔中的演变过程,重点研究了注入脉冲串种子光总能量和串内能量分布对放大输出脉冲串整体能量提取及串内能量分布的影响;从实验上研究了注入脉冲根数对再生放大输出光束指向稳定性的影响,通过增加注入脉冲根数和腔型优化,最终获得了光束指向稳定性优于±8.75μRad的再生放大光,且在空间各个方向上抖动较均匀;进行了行波放大实验,获得了输出平均功率为100W的1064 nm激光。5、基于有限元方法,理论模拟了不同状态下倍频晶体内部温度场分布,用于优化倍频方案。开展了高功率皮秒激光腔外倍频实验,研究了在同一脉冲串基频光泵浦条件下,不同倍频方案对二次谐波转换效率的影响以及脉冲根数对倍频效率的影响。通过增加多个4F空间像传递系统提高光束质量以及增加偏振片提高基频光束偏振纯度等措施,最终获得了功率大于50W、倍频转换效率达到68%、光束质量因子M~2小于3.4、功率长期稳定性优于1%的绿光。更多还原

【Abstract】 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 μRad 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%.更多还原