热晕对高功率列阵激光大气传输光束质量的影响

High-power laser array beams play an important role in applications of high-energy weapons and inertial confinement fusion, and so on. The thermal blooming effect is the important factor that affects the beam quality of high-power laser array beams propagating through the atmosphere. Until now, there are a few studies on this topic. The thermal blooming depends on the characteristic of the laser beam and the state of the atmosphere. The thermal blooming both in the stationary and non-stationary modes of high-power laser array beams propagating through the atmosphere is investigated in this project. The infulence of the thermal blooming on the 4 types of combined beams (i.e., coherently combined single mode laser, incoherently combined single mode laser, coherently combined multi-mode laser and incoherently combined multi-mode laser) is studied. Single mode or multi-mode, coherent combining or incoherent combining, which is in favor of reducing the thermal blooming on the beam quality, are examined. The infulence of the thermal blooming on the beam quality of high-power laser array beams propagating through the atmosphere along a slant path is studied. The difference of influence on the beam quality between the thermal blooming without turbulence and the thermal blooming with allowance for turbulence is examined. The influence of the array type, the element number, the fill factor and the aperture effect on the thermal blooming is also studied. The four-dimensional (4D) computer codes of the time-dependent propagation of high-power laser array beams through the atmosphere are designed in this project. The results obtained in this project will propose methods to reduce the thermal blooming of high-power laser array beams propagating through the atmosphere, and will provide the theoretical basis for applications of high-power laser array beams propagating through the atmosphere.

高功率列阵激光在激光能量远程输运和利用、惯性约束核聚变等领域中扮演着重要角色，而热晕效应是影响高功率列阵激光大气传输光束质量的重要因素，目前国内外对此研究甚少。热晕效应与光束形态和大气状态有密切关系，本项目拟研究高功率列阵激光大气传输的瞬态和稳态热晕效应，主要研究内容有：针对4种类型的合成光束（单模光束相干与非相干合成、多模光束相干与非相干合成），研究热晕对其光束质量的影响，探究单模与多模、相干与非相干合成哪种更有利于减小热晕对光束质量的影响；研究斜程大气热晕对列阵激光光束质量的影响；研究大气湍流条件下的热晕与单纯热晕对列阵激光光束质量影响的差异；研究列阵激光排列方式、子光束数目、填充因子以及光阑效应等因素对激光热晕效应的影响。本项目结果将提供减小热晕对列阵激光光束质量影响的途径、以及列阵激光束在大气中传输的四维仿真模拟程序，为工作在大气环境中的高功率列阵激光的相关应用提供理论基础。

高功率列阵激光在激光能量远程输运和利用、惯性约束核聚变等领域中扮演着重要角色。热晕效应是影响高功率列阵激光大气传输光束质量的重要因素，之前国内外对此研究甚少。因此，本项目编制了列阵激光束在大气中传输的四维仿真模拟程序，采用数值模拟和理论解析方法对此展开了详细研究。本项目主要研究内容、重要结果及其科学意义如下：（1）研究了热晕对截断光束光束质量的影响。研究发现：截断光束的光束扩展受热晕的影响小于非截断光束。光束重心位置随截断参数的变化是非单调的。（2）研究了热晕对列阵高斯光束大气传输的影响。研究发现：填充因子越大的列阵光束受热晕影响越小。相干合成的列阵光束比非相干合成的受热晕影响更大。相干合成的列阵光束最大光强始终大于非相干合成的，但是由于热晕效应的影响相干合成的传输效率并不总是大于非相干合成的。达到最大传输效率的最优填充因子的值随着激光功率的增大而增大，但是达到最大峰值的最优填充因子几乎与激光功率无关。同时，给出了与子孔径填充因子有关的扭曲参数的表达式。另外，研究了列阵高斯光束斜程传输，以及热晕和湍流综合效应对列阵高斯光束的影响。（3）研究了热晕对厄米高斯（H-G）光束大气传输影响。研究发现：相同功率情况下，H-G光束模式数越高，其热晕效应越弱。若采用像散参数评价光束的对称性，热晕效应可以改善原本非对称H-G光束的对称性。若选择合适的权重因子，热晕效应会使多模光束（TEMm0）在靶面上的光斑最小。同时，得到了与模式有关的扭曲参数的表达式。另外，对非相干合成的H-G光束以及多模列阵光束在大气中传输的热晕效应进行了研究。（4）研究了热晕对列阵平顶高斯光束大气传输影响。研究发现：光束阶数越大的列阵平顶光束受热晕影响越小。相同功率下，大气中列阵平顶光束的传输效率优于列阵高斯光束。本项目所得结果对合成高功率激光及其大气传输实际应用具有意义。