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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。
The half-wave hole problem has seriously affected the application of the frequency-doubling beam splitter in high-power laser systems. In order to study the generation mechanism of the half-wave holes, the half-wave holes of the 1/4 wavelength symmetric regularized film system were simulated respectively by the thickness mismatch of the high and low refractive index films and the dispersion loss of the film materials. Based on the theory of equivalent layer, the equivalent refractive index E of the film system is calculated on the Matlab platform, and the corresponding extreme value envelope curve of reflectivity is plotted. By studying the relationship between the equivalent refractive index, reflectance spectrum and reflectance envelope of the symmetrical membrane system, the characteristics, such as the size, position and changing trend of the half-wave pore, are analyzed theoretically. The results show that the thickness mismatch of the film causes the equivalent refractive index of the symmetric film system to produce a cutoff band at the half-wave spectrum. The more the number of layers, the more serious the mismatch between the thickness of the film and the chromatic dispersion of the film, the deeper the half-wave hole of the frequency-doubling beam splitter.