【作者】 周琼；

【导师】 姜宗福；

【作者基本信息】 国防科学技术大学 ， 光学工程， 2012， 博士

【摘要】 随着激光功率水平的不断提高，激光传输通道中的镜面和气体的热效应问题愈发严重，导致激光系统光学性能的下降。本文从镜面热变形和气体热效应的基础理论出发，以Comsol多物理场耦合软件和Matlab数学软件为计算工具，采用理论分析和仿真模拟等方法，围绕内光路通道的镜面热变形像差、气体热效应分析以及整体热效应的波前预补偿等内容展开了较为系统的研究。开展了内光路通道中反射镜热变形像差的数值研究，并建立了内光路通道的镜面热效应缩比模型。首先，分析了高反膜层的体变形对反射镜总体热变形的影响，并对不同的激光能量吸收方式下的反射镜热变形进行了对比，确定了在进行反射镜热变形像差计算时采用的面热源吸收条件。其次，对不同激光辐照条件下的反射镜热变形像差进行了计算和分析：在强度均匀分布的激光辐照条件下，分别计算了不同的吸收总功率、入射角度、辐照时间和相对尺寸等条件下的反射镜热变形分布，对计算结果进行了分析，并定义像差比率nm来量化热变形像差与各影响因素的关系；在强度分布不均匀的激光辐照条件下，对采用光束旋转的方式时反射镜的热变形像差进行了仿真计算，旋转角速度的增加可以有效的减少热变形像差中的高阶项成份。最后，依据反射镜的热变形尺度律和光学传输的等Fresnel数条件建立了内光路通道的等比缩放计算模型，并通过对其热变形像差分布及其Zernike多项式拟合系数的分析，建立了缩放模型与原始模型之间的数值反演关系。开展了L型内光路通道中气体热效应像差的仿真研究，并实现了内光路通道中镜面和气体的整体热效应像差仿真计算。对长时间加热条件下L型管道中气体热效应进行了仿真计算，并分析了气体热效应像差分布的时间特性，结果表明，随着工作时间的增长，气流的温度和密度极值位置会向管道出口处移动，且气体热效应像差的“双鱼眼型”结构也随之消失。结合镜面热变形和气体热效应的数值计算，实现了内光路通道中光场、温度场、应力/应变场和流场的多物理场耦合仿真，并对L型内光路通道的整体热效应像差和出射激光的光束质量进行了分析，结果表明：随着激光加热时间的增长，管道内的反射镜和气体的温升均趋于稳定，热效应像差均方根值的增加和出射激光远场光束质量的下降均趋于平缓。开展了内光路通道中反射镜热变形和气体热效应的波前预补偿仿真研究，并对热变形像差波前预补偿的不稳定性进行了分析。首先，分别对不同激光辐照条件下的热变形像差波前预补偿进行了计算和研究，结果表明：当激光的强度分布不均匀时，对于Fresnel数为NF=95的内光路通道，在反射镜吸收功率较大的情况下波前预补偿方式对系统光学性能的改善会更加明显；在强度分布均匀的激光辐照条件下，结合对反射镜热变形像差的分析结论，利用Zernike拟合多项式建立了内光路通道中热变形像差波前预补偿的简化计算模型，其数值仿真结果与原始模型能够较好的吻合。其次，分别考察了信标光的畸变相位误差、共轭校正精度和系统Fresnel数等因素对内光路通道中反射镜热变形像差波前预补偿的影响：当采用信标光的畸变波前作为共轭补偿相位时，分光镜的端面效应会使出射激光的畸变波前中高阶像差成分的比重增加；随着校正精度N的增加出射光的补偿相位残差逐渐减少，且当校正精度N高于20时，波前预补偿能够得到较好的校正效果；出射激光的远场光束质量随着系统Fresnel数的增大而提高，并逐渐趋于稳定。再次，对内光路通道中热变形像差的波前预补偿不稳定性进行了讨论和分析，当工作时间较短时波前预补偿的不稳定性表现较明显，随着系统工作时间的增长，激光的光束质量因子的变化趋于稳定。最后，对长时间激光加热条件下L型内光路通道中的热效应波前预补偿进行了仿真研究，结果表明：随着工作时间的增长，波前预补偿的相位残差均方根值逐渐增加，且其主要像差成分由初级像差变为主球差和第25阶像差。更多还原

【Abstract】 With the increase of laser power, the thermal effect of mirror and gas in the beampath is serious, which causes the decrease of the optical performance of laser system.Based on the basic theory of the thermal deformation and gas thermal effect, by usingthe Comsol multiphysis simulation software and Matlab calculation software, contentsincluding the aberration caused by thermal deformation and gas thermal effect, thewavefront pre-compensation of whole thermal effect in the inner beam path areinvestigated in theory and simulation in this thesis.The thermal deformation aberration of mirrors in inner beam path is studied insimulation, and the scaling model for an inner optical system is designed. Firstly, theinfluence of deformation of reflection coating on the thermal deformation of mirror isanalysed. The thermal deformations on different absorbtion conditions are comparatedand the surface heat condition is choosed to calaulating of thermal deformationaberration. Secondly, the thermal deformation of reflector is calculated and analysed onvary laser irradiation condition. When the distribution of absorption intensity is even,the influence of absorptiton power, angle of incidence, irradiation time and relative sizeon thermal deformation is studied respectively, and the abrration ratio nmis defined todescribe this relation. When the distribution of absorption intensity is uneven, theinfluence of beam rotation on thermal deformation is analysed, and the result shows thatwith the increase of rotation velocity the high-order aberration is decreased. Finally,based on the angular spectrum diffraction theory of light, the heat conduction theory andthe thermal elastic theory, the thermal deformation aberration and the wavefrontpre-compensation are simulated for both models. The scaling model can be numericallytransformed to original model.The distribution and time characteristic of gas thermal effect in a L shaped innerbeam path is discussed, and the thremal effect containing thermal deformation and gasthermal effect is claculated in simulation.The gas thermal effect distribuytion in a Lshaped inner beam path is calculated by using Comsol muli-physics software. Onconditon that the irradiation time is long the peak value spot of temperature and densityis moved to exit of pipe and the characteristic of ’double pearl eye’ structure is disappear.The coupling of beam field, temperature field, stress/strain field and fluid field in aninner beam path is simulated. The thermal effect of L shaped path and the beam qualityof outgoing laser are analysed. With the increase of heat time the temperature rise ofmirror and gas in pipe is steady, and the thermal effect and beam quallity of laser arechanged no more.The wavefront pre-compensation of thermal deformation and gas thermal effect ininner bam path is studied in simulation and the thermal effect compensation instabilities is analysed. Firstly, the thermal deformation pre-compensation on vary laser irradiationcondition is calculated and studied respectively. The results show that on condition thatthe distribution of absorption intensity is uneven, the active influence of wavefrontpre-compensation on the optical performance is more obvious when the value ofirradiation power is higher. On condition that the distribution of absorption intensity iseven, based on the analysis conclusion of thermal deformation aberration of mirrors, thesimplification calculation model of thermal deformation pre-compensation in innerbeam path is established with Zernike polynomials. Secondly, the influence of distortionphase error of beacon, precisions of adaptive conjugation correction and general Fresnelnumber on thermal deformation pre-compensation in inner beam path is studiedrespectively. When the distortion phase of beacon is used as conjugation correctionphase the proportion of high-order aberration in outgoing laser phase is increasedbecause of thermo-optic effect. The residual phase is decreased with increase ofprecisions of adaptive conjugation correction N, and when N>20, the correction ofthermal deforamtion aberration is more obvious. With the increase of general Fresnelnumber the beam quality in far field of outgoing laser is increased. Then, the thermaldeformation pre-compensation instability in inner beam path is studied and analysed.When the irradiation time is little, the instability of compensation is obvious. With theincrease of irradiation time the increase of beam quality factor is slow down.Finally, on condition that the irradiation time is long the thermal effect compensation ofL shaped path is studied in simulation. The results show that with the long irradiationtime the residual phase is increased.更多还原