Nonscanning computed tomography imaging spectropolarimeter (NS-CTISP): design and calibration

The Non-Scanning Computed Tomography Imaging Spectropolarimeter (NS-CTISP) is a novel imaging spectropolarimeter developed for snapshot imaging and collection of the four Stokes hyper-cubes. The patent pending NS-CTISP builds upon the computed tomography concepts proven in earlier imaging spectrometers and imaging spectropolarimeters by utilizing a combination of two-dimensional spectral dispersion and division of aperture polarization analysis to acquire all data necessary to estimate the Stokes hyper-cubes without scanning in spatial, spectral or polarimetric dimensions. A custom quadrant polarization analyzer and tetrahedron prism are used in tandem to perform aperture division and polarization analysis on each of the four pupils. Equations are developed which link the computed tomography spectral reconstruction and polarimetric calibration allowing the determination of Stokes vectors at each waveband. NS-CTISP is spectrally and polarimetrically calibrated by measuring the system's spectral and polarimetric response to a radiating object having a small spatial extent, limited spectral bandwidth and a pure polarization state using a monochromator, fiber and polarization state generator. Iterative techniques are used to solve a linear imaging equation, where the solution provides input into the polarization calibration. Preliminary estimates of calibration fundamental accuracy indicates the average Stokes parameter error for central wavebands is on the order of 1.4-1.8 percent. A simple pseudo-object is created using two different fiber images each having a different polarization and reconstructed with average Stokes parameter error ranging from 0.7% to 3.2%. A suite of data acquisition, reconstruction and display programs have been developed in Interactive Data Language (IDL) to support NS-CTISP development.