像差对三镜型线聚焦滤波器效能影响的数值研究

Numerical Research into Aberration Effect on Efficiency of Three-Lens Slit Spatial Filter

线聚焦滤波技术能够大幅缓解甚至解决目前聚变装置中的等离子体堵孔效应及激光装置规模庞大等问题,在聚变激光装置中具有较广阔的应用前景。采用像差的衍射理论,分析了各类像差对三镜型线聚焦滤波器效能的影响。给定滤波系统中评判像差影响时采用的两个重要参量(输出光束的近场对比度及滤波狭缝的内边缘强度)及其容许范围;在滤波器中引入不同类型和大小的像差,根据参量的变化获得各类像差的容许值,并与传统的针孔滤波器进行对比。结果表明:透镜上存在的各类像差都会导致波面上产生各种非均匀的相位变化,并降低光束质量,而像差导致的弥散或形变也会使滤波狭缝内边缘的辐照强度发生变化,即随像差增大而不断降低。对三镜型线聚焦滤波器效能影响最大的像差来自于第一块柱面镜上的球差和场曲。

Slit spatial filtering technology can be used to significantly ease or even solve problems related to plasma pinhole closure and large scale in current high-power lasers for fusion,which has broad application prospects in fusion laser facilities.According to the diffraction theory of aberrations,this paper numerically analyzes the aberration effect on efficiency of a three-lens slit spatial filter.Two important parameters(near-field contrast of output beam and intensity on inner edge of filter slit)are considered as evaluation parameters of aberration effect in a given filtering system,and the permitted percentages to be changed are given.Different types of aberrations with different magnitudes are introduced into the filtering system,and the tolerance of each aberration is obtained according to the change of parameters.The introduced filtering system is compared with conventional pinhole filters.The results demonstrate that all types of aberrations on the lens may introduce various inhomogeneous phase changes in the wave-front of a light beam and degrade beam quality.In addition,dispersion or deformation caused by aberrations may change the intensity irradiated on the inner edge of slit apertures,which is reduced continuously with increased aberrations.The most noteworthy aberrations relative to the three-lens slit spatial filter are the spherical aberration and field curvature of the first cylindrical mirror.