改型Wollaston棱镜干涉光谱仪的调制度研究

Study on Modulation Degree of Fourier Transform Spectrometer Based on Modified Wollaston Prism

摘要:

改型Wollaston棱镜(MWP)无需中继,可构建微型傅里叶变换光谱仪。回顾了MWP的基本原理,从调制度定义出发,计算得到准单色光源的复相干度,找到调制度的影响因素——扩展视场、剪切结构、焦面探测等。建立一般的干涉定域分析模型后,由像点逆光路追迹给出MWP的厚度计算公式,代入调制度约束参数得到不同参量的误差容限。通过FRED记录不同视场扩展情况的灰度与辐照度,结果显示,调制度为0.9时,视场与理论估算值1.24°基本相符;不同剪切量的灰度与辐照度变化特性表明,结构角会使定域垂直系统光轴的入射角发生变化,与晶轴倾角共同影响双折射率差;2.5和8μm像元探测采样表现出调制度差异,描述了定域深度或离焦的影响。以准单色光源、复相干度表示调制度,可将不同影响因素统一至约束参数中,相关变量误差容限可作为MWP-FTS的设计依据。

Abstract:

The modified Wollaston prism (MWP) whose optical axis is tilted can be constructed into a micro Fourier-transform spectrometer (FTS) without a relay lens to project the image. By reviewing the basic principle of MWP, through the definition of fringe visibility, the complex interference degree of the quasi-monochromatic light source was calculated, thus the related factors such as the FOV, shearing structure, focal plane detection, and etc were indicated. Based on the established general fringe localization model, the thickness calculation formula of MWP was given by tracing the imaging point back, and the error tolerance of different parameters was obtained. By testifying the interference of the quasi-monochromatic light source via FRED, the visibility results showed that the FOV (visibility 0.9) is basically the same as the theoretically estimated value. The FRED results show that the shearing angle changed the incident angle needed to make the fringe localization plane formal to the axis of optical system, influencing the refractive index difference together with the crystal axis inclination angle. Finally, the visibility difference of the sampling pixel of 2.5 and 8μm describes the effects of localization depth or defocus. The modulation degree is represented by the complex coherence degree of the quasi-monochromatic light source, making different influencing factors be unified to constraint parameters, and thus the error tolerance can be used to design MWP-FTS.