Dispersive effects in imaging polarimetry based on a wire-grid polarizer.

We explore effects of light dispersion by a wire-grid polarizer (WGP) in imaging polarimetry. The dispersive characteristics of a WGP, combined with off-axis scene incidence, cause significant non-uniformity. The normalized performance measure of contrast due to dispersion of WGP exceeded 0.84 for transmittance and 0.90 for extinction ratio (maximum non-uniformity at 1 and 0 for uniform performance). Dispersion also produces a lateral spread in the imaging plane, which may induce spectral image misregistration. Without higher-order excitation, the misregistration can be at the least a few pixels long in the detector. In the presence of higher-order modes, the dispersive misregistration can be severe and critical for polarized scene extraction. The results emphasize the need for an imaging polarimeter to be designed to manage the dispersive effects.