基于3PEMs和AOTF的光谱偏振成像系统及光谱修正

Optical System Design and Spectral Correction Based on 3PEMs and AOTF Spectropolarimetric Imaging

基于弹光调制器和声光可调谐滤波器(AOTF)的新型光谱偏振成像系统部件多,AOTF入射角小,同一幅图中光谱分布不均。为此提出了一种前置光学系统由凸透镜、凹透镜和凸透镜构成的光学系统,压缩被测目标视场角,使其满足AOTF视场角要求,并将目标平行入射光变为平行光入射进AOTF,以便光谱修正。不同位置的目标以不同入射角依次进入光学系统和AOTF,在CCD上的成像位置也不同。AOTF的衍射光中心波长与入射角有关,可通过拟合测得衍射波长与入射角的关系,进而得到CCD像元与中心波长的关系,并对光谱修正方法进行了详细分析。实验结果表明,修正后的光谱测量误差比普通的AOTF光谱成像平均降低一个数量级,且成像清晰,提高了光谱偏振成像系统的光谱测量精度。

The spectropolarimetric imaging system based on three photoelastic modulators and one acousto-optic tunable filter （AOTF）, has many components, limited field angle of AOTF and uneven spectral distribution in one image. To overcome the disadvantages, an optical imaging system is reported, in which the front optical system is composed of convex lens, concave lens and convex lens. The field angle of measured target is compressed so as to satisfy the requirement of the AOTF field angle. The parallel incident light of the target is changed to parallel light incident into AOTF for subsequent spectral correction. Target light at different positions enters the optical system and AOTF with different incidence angles, and the imaging positions on CCD are also different. Since the central wavelength of the AOTF diffracted light is related to the incidence angle, the relationship between them can be determined by fitting, which further identifies the relationship between the central wavelength and the CCD pixel. The spectral correction method is analyzed in detail. The experimental results show that the error of corrected spectral value is reduced by an order of magnitude compared with that of the common AOTF spectral imaging system. The spectral imaging results are clear and the accuracy of the speetropolarimetric imaging measurement system is improved.