长脉冲YAG激光放大器的研究

发布时间：2018-03-23 03:39

本文选题：YAG激光器　切入点：MOPA结构　出处：《华中科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：本论文对千瓦级长脉冲Nd:YAG固体激光放大器进行了理论分析和实验研究。首先,在时间域和空间域对激光器振荡级和放大级进行了分析和模拟,得到了耦合输出镜透过率、输出功率、提取效率、高斯光束传输特性以及增益特性等方面的理论分析结果,确定了激光器的结构参数。该结构保证各级之间高斯光束匹配,使入射光束恰好充满介质棒的端面,充分利用有效模体积的同时进行自孔径选模,抑制热致球差对M2因子的负面作用。经过调整各级的间距和热焦距的匹配,得到放大级不改变传输光束BPP的结果。然后,针对强泵浦、高功率固体激光器,基于非线性模型进行了热效应分析。研究了[111]切割方向Nd:YAG激光介质热致双折射与其偏振特性,给出了激光介质纵向截面内热致双折射椭圆分布图。根据对非线性模型的光程差拟合分析,得出半径相关的二次项对热焦距产生贡献,而四次项决定了热透镜球差,高功率情况下热致球差不能忽略,并且会影响光束质量的结论。根据热致双折射所导致的折射率变化重新分析了基于非线性模型的热焦距,实测值与理论值的吻合度比线性模型更高。最后,实验采用单级振荡两级放大的MOPA结构,在重复频率为90 Hz,脉冲宽度为1 ms时,得到1024 W的平均输出功率,输出激光的单脉冲能量11.4 J,峰值功率11.4 kW,电光效率3.41%,BPP=20.9 mm×mrad。其中振荡级BPP=19.8 mm×mrad,通过两级放大,BPP在误差范围内基本保持不变,符合预期设计目标。与同级别千瓦级的腔内串接固体激光器比较,MOPA结构固体激光器的BPP更小,电光效率较高,另外还能避免腔内激光介质和光学元件的光损伤,从而降低系统的组装、调试以及维护等方面的复杂度。
[Abstract]:In this paper, the theoretical analysis and experimental study of kilowatt-class long-pulse Nd:YAG solid-state laser amplifier are carried out. Firstly, the laser oscillation stage and amplifier stage are analyzed and simulated in time domain and space domain, and the transmittance of coupling output mirror is obtained. The theoretical analysis results of output power, extraction efficiency, beam propagation characteristics and gain characteristics of Gao Si have determined the structural parameters of the laser. The incident beam is filled with the end surface of the dielectric rod, and the self-aperture mode selection is carried out by making full use of the effective mode volume to suppress the negative effect of the thermal spherical aberration on the M2 factor. The results of the amplification stage without changing the propagating beam BPP are obtained. Then, the thermal effect analysis is carried out based on the nonlinear model for strongly pumped, high-power solid-state lasers. The thermally induced birefringence and polarization characteristics of the Nd:YAG laser medium with the cut direction are studied. The thermal birefringence ellipse distribution in the longitudinal section of laser medium is given. According to the optical path difference fitting analysis of the nonlinear model, the quadratic term related to the radius contributes to the thermal focal length, and the fourth term determines the spherical aberration of the thermal lens. The conclusion that thermal spherical aberration can not be ignored and will affect the beam quality under high power condition is concluded. The thermal focal length based on nonlinear model is reanalyzed according to the refractive index variation caused by thermally induced birefringence. The agreement between the measured and theoretical values is higher than that of the linear model. Finally, a single-stage oscillatory two-stage amplified MOPA structure is used to obtain an average output power of 1024 W at a repetition rate of 90 Hz and a pulse width of 1 Ms. The single pulse energy of the output laser is 11.4 J, the peak power is 11.4 kW, the electro-optic efficiency is 3.41 and the BPP is 20.9 mm 脳 mrad.Oscillation stage BPP=19.8 脳 mrad. through two-stage amplification, the BPP remains basically unchanged within the error range. The BPP of MOPA-structured solid-state laser is smaller, the electro-optic efficiency is higher, and the optical damage of the laser medium and optical elements in the cavity can be avoided, compared with the intracavity series solid-state laser with the same level of kilowatts. In order to reduce the system assembly, debugging and maintenance and other aspects of the complexity.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN722

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