激光辐照下腔镜热变形对光场模式影响研究

发布时间：2018-03-05 18:22

本文选题：激光器　切入点：腔镜　出处：《国防科学技术大学》2015年硕士论文　论文类型：学位论文

【摘要】：本文以高能激光器中常用的正支虚共焦非稳腔为研究对象,讨论分析了激光辐照下腔镜热变形对光场模式的影响,研究结果可以为长时间工作条件下高能激光器谐振腔输出光束特性分析及后续光束控制提供一定指导意义。论文主要研究内容有:基于角谱传播法的谐振腔光场模式分析,激光辐照下腔镜热变形的计算,腔镜热变形对光场模式的影响研究,不同光束对发射系统聚焦距离的影响研究等,主要研究内容如下:1.建立了基于角谱传输法的谐振腔光场模式的计算模型,采用腔镜光阑边缘“软化”处理、有源腔内增益薄层分布等方法,实现了光场模式的数值计算。完成了基于MATLAB的谐振腔光场模式计算程序编写,计算了正支非稳无源腔的光场模式,将计算结果与文献报道对比,验证了计算程序的正确性。分析计算了三种有源腔的光场模式,计算结果表明,光场振幅分布与腔内小信号增益的分布有关,小信号增益分布不含相位扰动时,相位分布主要由谐振腔结构决定,输出波面近似平面。2.开展了激光辐照下腔镜温升和热变形的分析研究,在腔镜热变形控制方程及有限元分析方程的基础上,完成了基于ANSYS软件的命令流控制程序编写,实现了温升和变形的数值计算,计算结果表明,腔镜温升和变形随激光功率和辐照时间增加而增加,正支非稳高能激光谐振腔中,次镜温升与变形大于主镜,较大的腔镜热变形对激光器输出光场存在影响。3.采用时间离散化、光场模式与腔镜变形序列耦合等方法,研究了出光时长较长时腔镜热变形对光场模式的影响,计算了出光4s时谐振腔输出光场的振幅分布、相位分布及对应的远场光斑。计算结果表明,出光过程中,腔镜热变形导致激光器输出光场发生变化,波面逐渐发散,文中计算条件下,由出光初始时刻的近似平面变为出光结束时刻的近似发散球面,其远场光斑在y方向分裂为上下两个光斑。试验验证了腔镜热变形对激光器输出光场的影响,讨论分析了采取腔镜背面冷却措施时的温升、变形及对光场的影响。4.解析推导了激光发射光学系统发射平面波、球面波、高斯光束时的聚焦距离与调焦量的关系,计算了激光发射光学系统发射平面波、球面波、高斯光束时的聚焦距离。结果表明:望远镜相同的调焦量下,球面波的聚焦位置、平面波的聚焦位置与高斯光束的束腰位置存在偏差,可通过增加高斯光束的束腰宽度、增大发射系统的扩束比等方法,减小高斯光束与平面波的聚焦距离差,可通过增大球面波的曲率半径,减小球面波与平面波的聚焦距离差;当要求聚焦距离一致时,需根据发射光束特征,对望远镜的调焦量进行调整,如果按照平面波的方法对球面波进行聚焦发射,聚焦位置必定偏离预定位置。
[Abstract]:In this paper, the influence of the thermal deformation of the mirror on the mode of optical field is discussed and analyzed, which is commonly used in high energy laser, and the positive branch and virtual confocal unstable resonator is used as the research object. The results can provide some guidance for the analysis of the output beam characteristics of the high energy laser resonator and the subsequent beam control under the condition of long time operation. The main contents of this paper are as follows: the optical field mode analysis of the resonator based on the angular spectrum propagation method. The calculation of the thermal deformation of the mirror under laser irradiation, the study of the influence of the thermal deformation of the mirror on the mode of the light field, the study of the influence of different beams on the focusing distance of the emission system, etc. The main research contents are as follows: 1. The calculation model of optical field model of resonant cavity based on angular spectrum transmission method is established. The method of "softening" the edge of the mirror diaphragm and the distribution of gain thin layer in the active cavity are adopted. The numerical calculation of the optical field mode is realized, and the calculation program of the optical field mode of the resonator cavity based on MATLAB is completed, and the optical field mode of the positively supported unstable passive cavity is calculated. The calculated results are compared with those reported in the literature. The calculation results show that the amplitude distribution of the optical field is related to the distribution of the small signal gain in the cavity, and the small signal gain distribution does not contain phase perturbation. The phase distribution is mainly determined by the structure of the resonator, and the output wave surface is approximately plane. 2. The temperature rise and thermal deformation of the mirror under laser irradiation are analyzed and studied. Based on the governing equation of the thermal deformation of the mirror and the finite element analysis equation, The command flow control program based on ANSYS software is completed, and the numerical calculation of temperature rise and deformation is realized. The results show that the temperature rise and deformation increase with the increase of laser power and irradiation time. The temperature rise and deformation of the secondary mirror are larger than that of the primary mirror, and the larger thermal deformation of the mirror affects the output light field of the laser. 3. The method of time discretization and coupling of the light field mode with the mirror deformation sequence is adopted. The influence of the thermal deformation of the mirror on the mode of the light field is studied when the time is long. The amplitude distribution, the phase distribution and the corresponding far field spot of the output light field of the resonator are calculated when the output light is 4 s. The calculation results show that, in the process of light output, the distribution of the amplitude, the phase distribution and the corresponding far field spot are calculated. The thermal deformation of the mirror causes the laser output light field to change, and the wave surface gradually diverges. In this paper, the approximate plane at the initial time of the light is changed into the approximate divergent sphere at the end of the light. The far-field spot splits into two spots in the y direction. The effect of the thermal deformation of the mirror on the output light field of the laser is verified by experiments, and the temperature rise is discussed and analyzed when the cooling measures on the back of the mirror are taken. The relationship between the focusing distance of laser emitting optical system and the focusing quantity of Gao Si beam is derived analytically, and the plane wave and spherical wave emitted by laser emitting optical system are calculated. The results show that the focusing position of spherical wave and plane wave are different from those of Gao Si beam under the same focusing range of telescope, which can be increased by increasing the waist width of Gao Si beam. By increasing the beam expansion ratio and decreasing the focusing distance difference between Gao Si beam and plane wave, the focusing distance difference between spherical wave and plane wave can be reduced by increasing the curvature radius of spherical wave, and when the focusing distance is the same, The focusing quantity of the telescope should be adjusted according to the characteristics of the emitting beam. If the spherical wave is focused according to the plane wave method, the focusing position must deviate from the predetermined position.
【学位授予单位】：国防科学技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN248

【相似文献】