The Research On Spectropolarimetric Imaging System And Imaging Quality Based On AOTF

As a combination of space, spectrum and polarization measurement of modern photoelectric measurement technology, it has potential application value and developing prospects in photoelectric detection areas such as space exploration,features remote sensing, chemical analysis, national defense military and so on. As the core component of phase modulation and spectral choice in spectropolarimetric imaging(SPI) system,the performance of Liquid crystal phase variable retarder(LCVR) and acousto-optic tunable filter(AOTF) directly affect the measuring accuracy and stability of SPI. Due to the dispersion characteristics of AOTF crystal,imaging quality decline and wavelength-dependent image definition difference are important factors to the decline in system practicability.Therefore, how to improve imaging quality and keep images clear under different wavelengths, make the spectropolarimetric imaging system receive real gray image of the target object under different wavelengths, has become the important science problems need to be solved for researching on SPI, which AOTF as a spectral selection device.Based on the measuring principles and imaging characteristics of new spectropolarimetric imaging system, whose core components are LCVR and AOTF,the paper makes study on the image quality of SPI and develops the high image quality spectropolarimetric imaging platform, together with its drive and control system.Firstly, the influence mechanism on the image quality of spectropolarimetric imaging system caused by the dispersion characteristics of AOTF is studied.Based on the dispersion characteristics of acousto-optical interaction crystal TeO2 in AOTF, the focus length is wavelength-dependent when diffraction beam imaging clearly in different wavelengths, it is analysed under secondary imaging mechanism and put forward the scheme of automatic focus. In view of the system problems of spectral broadening in diffraction direction, the specific causes of the spectral broadening is analysed in the diffraction angle of deflection and diffraction efficiency two aspects.The influence mechanism of dispersion characteristics in AOTF and the imaging quality in spectropolarimetric imaging system is verified through experiments,the results laid the theoretical basis and experimental evidence for research on image quality of SPI.Secondly, a new hyperspectral full polarization imaging technologies based on LCVR and AOTF is researched. Based on the stokes polarization measurement theory,the polarization models of LCVR and AOTF were established, as well as their mueller matrix. A hyperspectral full polarization imaging system realizes spectral selection with an AOTF, phase modulation with a LCVR and two CCD cameras to image diffraction beam on ±1 orders, the measuring principles of the system were introduced and the stokes vector measurement model was also deduced, then the influence of the angle between LCVR fast axes and X axis, phase delay of tiny changes were analyzed,the error value has been verified with the experimental platform.Thirdly, in order to reduce the influence on image quality of SPI caused by the dispersion characteristics in AOTF, an automatic focus image quality evaluation function is presented based on the imaging characteristics of system whose core components are LCVR and AOTF. Based on the research on characteristics of variety of image sharpness evaluation function, according to the system imaging features, a new image sharpness evaluation only consider the brightness and contrast correlation in diffraction direction is put forward, which named ELSSIM evaluation function. The system imaging characteristics was verified through image analysis under different focal lengths and different wavelengths.Use ELSSIM and Gradient-operator-based evaluation function to evaluate the experimental images, the calculation advantage of the former can be concluded.The hardware and program of control system are also finished combined with auto-focus search algorithm.Finally, combined with the auto focus scheme and spectropolarimetric imaging technology, a spectropolarimetric imaging measurement platform is built by integrating the auto focus scheme.in order to verify its feasibility and practicability.Image on target objects with the measurement platform,and the results show that the system can achieve the best image quality under different wavelength and polarization and spectral characteristics of targets through analysis images, to achieve the purpose of target resolution.