基于声光滤光和液晶相位调谐的高光谱全偏振成像新技术∗

摘要

为了获取高光谱分辨率、高空间分辨率、高偏振精度、高信噪比和稳定性好的全部Stokes 参量光谱图像,考虑到声光可调谐滤光器(acousto-optical tunable filter, AOTF)的±1级衍射光的正交特性,提出用一个AOTF滤光,一个液晶可变延迟器(liquid crystal variable retarder, LCVR)进行相位调制和两个CCD相机分别对±1级衍射光成像的高光谱全偏振成像新技术.从所采用的光学元件的穆勒矩阵出发,阐述了该技术的基本工作原理；理论分析表明, LCVR不但不会影响到第一个Stokes参量的探测精度,而且后3个Stokes参量的相对误差分别优于0.064%,0.31%和3.97%；利用原理样机获取了450—700 nm、光谱带宽为10 nm的26个光谱通道的图像数据,成像质量良好；以工作波长为600 nm的入射光为例,对其全部Stokes参量图像进行了具体分析讨论.结果表明,该新技术原理正确,方案可行.该研究可为光谱偏振成像技术提供新的理论和实现方案.%In order to achieve all Stokes parameters of spectral image with high spectral resolution, high spatial resolution, high polarization accuracy, high signal-to-noise ratio and good stability, taking into account the orthogonal characteristic of ±1 order diffraction light which diffracts from a acousto-optic tunable filter (AOTF), a new technique of full polarization hyperspectral imaging is presented. It uses one AOTF to diffract the incident light, one liquid crystal variable retarder (LCVR) to modulate the light retardation, and two CCDs to image the ±1 order diffraction light, respectively. According to the Muller matrixes of all optical elements in the system, the basic working principle of the new technique is that LCVR sequentially provides the retardation 2π, 1.5π,πand 0.5πfor each spectral channel, so the CCD obtains corresponding images. After analyzing these images, the all Stokes parameters are obtained;the precision of this system for polarization imaging is determined mainly by polarization modulation device LCVR. Considering the azimuth of LCVR fast axis and retardation precision at the same time, it is unveiled that LCVR has no effect on the accuracy of the first Stokes parameter, and the relative errors of other latter 3 Stokes parameters are less than 0.064%, 0.31% and 3.97%; then, our prototype system is used to do the outdoor experiments in a summer sunny morning, images data for 26 spectral channels with spectral bandwidth of 10 nm, which are from 450 nm to 700 nm, are acquired, the imaging quality is very fine. Firstly, LCVR are not assembled in our prototype system, and AOTF works in the sweeping frequency mode. The spectrum from each CCD proves that the diffraction efficiency of AOTF ±1 order diffraction light is not completely the same, and the difference must be considered in polarized image processing. Then another experiment is done after LCVR has been assembled. The image data of the incident light of 600 nm are taken for example to discuss its all Stokes parameters in detail. The results show that the principle of the new technique is correct and the new scheme is feasible. This study provides a new theory and implementation scheme for the polarization spectral imaging technology.