Faceted grating prism for a computed tomographic imaging spectrometer

A computed tomographic imaging spectrometer (CTIS) disperses the three-dimensional (3-D) datacube (x, y, lambda) into two-dimensional (2-D) projections on a focal plane array (FPA). The 3-D datacube is subsequently reconstructed from these 2-D projections using iterative computed tomography algorithms. Conventional designs achieve the 3-D to 2-D mapping by incorporating an optimized disperser. However, these dispersers suffer from the linearity constraint inherent in the first-order grating equation. This constraint means that many of the FPA's pixels are either unilluminated or they are used to image redundant projections; in both cases, they can not be used to increase the datacube's spectral resolution. Here, we outline various hardware improvements that increase the CTIS's spectral resolution by making use of these previously unilluminated or redundant pixels. Specifically, we incorporated a new disperser based on a 2-D grating prism and a division of aperture approach. Included is an optical design analysis of the system, in addition to an experimental characterization of the instrument's performance. Lastly, the new disperser is compared to a conventional disperser to quantify the increased spectral resolution. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.OE.51.4.044002]