Channeled spectropolarimetry based on division of aperture and field of view

Abstract

In order to obtain accurate image, spectrum and polarization state of target by the interferometric channeled spectropolarimeter, the interferogram and the image need to be separated. Although it can be achieved by digital image processing technology, heavy computations with approximation would be introduced. In the application of channeled spectropolarimetry, an inevitable crosstalk will be present between channels of the interferogram formed on the CCD. Spatial filtering in the optical path difference domain will generate a loss of spectral resolution and the distortion of the recovered spectrum. To overcome these drawbacks, a static imaging channeled spectropolarimeter based on division of aperture and field of view is presented. The aperture is divided by a polarization array, which consists of two polarizers with their transmission axes perpendicular to each other. The field of view is divided by a pair of lenses with the same focal lengths. The spectral modulation module is composed of an achromatic quarter wave plate, a retarder and a polarization array. The interference system consists of an achromatic half wave plate, a Wollaston prism, and a Savart polariscope. Two pairs of in-phase and anti-phase interferogram with different intensity modulations can be obtained simultaneously on a single detector array. The pure image of the target is acquired by the summation of the four interferograms. The background intensity is removed by the subtraction of the interferograms with in-phase and anti-phase, and the pure interference fringes can be acquired. By the summation and subtraction of the two pure interference fringes, the single channeled interference fringes corresponding to spectrum of intensity and linear polarization state can be obtained. Spectral and polarization information of the target are acquired by Fourier transform of the single channeled interference fringes. Compared with previous instruments, the described model has the significant advantage that the background intensity can be removed from the hardware of the layout, and thus avoiding the spatial filtering in the optical path difference domain. The obtained spectra have the same resolutions as those obtained from the interference system, and the distortion of the recovered spectrum can also be vanished. Since there is neither rotating part nor moving part, the system is relatively robust. In the present paper, the principle of the instrument is described, and the interference fringe intensity distribution formula is obtained and analyzed. The performance of the system is demonstrated through a numerical simulation. This work will provide an important theoretical basis and the practical instruction for designing a new type of imaging sepctropolarimeter and its engineering applications.