偏振型干涉成像光谱仪中Savart偏光镜通光孔径的研究

Analysis of the clear aperture of Savart plates in polarization interference imaging spectrometer

论述了偏振型干涉成像光谱仪的核心部件——Savart偏光镜的结构和分光机理.应用波法线追迹的方法,对光在任意方位入射面内,以任意入射角入射时Savart偏光镜中的光线传播规律及出射光孔径变化进行了理论推导,给出了出射孔径与入射位置、入射角及入射方位角之间满足的关系,并讨论了光线传播始终处于Savart偏光镜晶体内部,最终从出射面射出所需满足的条件.采用计算机模拟,给出了光线垂直入射时,出射孔径的表达式,验证了推导的正确性;在此基础上对自行设计的干涉成像光谱仪通光孔径进行了详细分析和讨论,结果表明通光孔径精确值和近似值之间存在较大差异.给出了孔径面积利用率随入射方位角的变化曲线,阐明在干涉成像光谱仪的参数论证以及孔径光阑的选取中,不能忽略由于晶体双折射现象带来的孔径变化.研究结果可为偏振型干涉成像光谱仪的设计、研制、调试和工程化提供重要的理论依据和实践指导.

The principle of beam splitting of interference imaging spectrometer based on Savart plates is presented. The propagation track of light wave in crystal and the exit aperture is analysed by combining wave normal-tracing method with ray-tracing method at random incidence angle and azimuth angle. The relationship among exit aperture, incident angle, incident position and azimuth angle is deduced in detail. The requirements that the propagation track of light remains in Savart plates and would not exit from the top surface, bottom surface and side are discussed in detail. The area and the position of exit aperture are simulated by computer, which proves the correctness of the deduction for normal incidence of light. It is shown that the lateral shear of single Savart plate restricts the boundary of clear aperture, and the area of the clear aperture is only 85.73~ against the total incident surface. The parameter of experimental prototype is introduced and the clear aperture is in detail analysed and discussed by the method mentioned above. The results show that the accurate and the approximate values of exit aperture area of experimental prototype are greatly different, and the position of exit aperture are shifted into the lower right, which may reduce the image quality and even cannot generate the double-beam interference fringes in some specific areas. The effective clear aperture as a function of azimuth angle is also presented. It shows that the used clear aperture area is between 0.8005 and 0.8547 while w changes from 0 to 2π, in order to match the conditions that the value of area availability decreases to 0.6976 when the light always propagates inside the Savart plates. The article shows that the change of clear aperture caused by crystal birefringence phenomenon cannot be ignored when selecting the instrument aperture stop and parameter of interference imaging spectrometer. The clear aperture of the two beams, o-light and e-light, which propagate in Savart plates should be calculated respectively and then they are used to determine the last clear apertures of plates. This study provides a theoretical and practical guidance for study, design, modulation, experiment and engineering of interference imaging spectrometers.