基于等效层法分析对称性倍频分束镜的半波孔

半波孔问题严重影响了倍频分束镜在高功率激光系统中的应用。为研究半波孔的产生机理,分别模拟了由高、低折射率膜层厚度失配和膜料色散失配引起的1/4波长对称规整膜系的半波孔。基于等效层理论,在Matlab平台上计算膜系的等效折射率E,绘出其对应的反射率极值包络曲线。通过研究对称膜系的等效折射率、反射率光谱和反射率包络之间的关系,从原理上分析了半波孔的大小、位置和变化趋势等特点。结果表明,膜层的厚度失配使对称膜系的等效折射率在光谱半波处产生截止带。膜层数越多,膜层厚度和膜料色散的失配越严重,则倍频分束镜的半波孔越深。

Analysis of the Half-Wave Hole for Symmetrical Harmonic Beam Splitter Based on Equivalent Layer Theoretics

Half-wave hole has seriously influenced the application of harmonic beam splitters in high-power laser systems. Half-wave holes of the quarter wavelength symmetrical coatings usually caused by overall thickness mismatch and materials dispersion mismatch of the high and low refractive index films are simulated in order to conduct further research on their formation mechanism. Based on the theory of equivalent layers, the equivalent refractive index of a symmetrical design is calculated on Matlab platform. Consequently, the corresponding reflectance envelope is depicted. Through the study on the relation among the equivalent refractive index, reflectance spectrum and reflectance envelope of different designs, the characteristics of half-wave holes such as location, size and change tendency are analyzed in principle. Computational results indicate that thickness mismatch gives rise to equivalent refractive stop-band in the half wave of spectrum. The more the number of layers is, the more serious the thickness mismatch and dispersion mismatch are, the deeper the half-wave hole will be for a harmonic beam splitter.