Measuring the spectral response of a division-of-focal-plane polarization imager using a grating monochromator

Abstract

Spectral characterizations are performed on imagers to obtain a relative spectral response (RSR) curve. This process often utilizes a grating monochromator with an output that changes polarization as a function of wavelength (our monochromator’s degree of linear polarization was found to vary from less than 10% to more than 70%). When characterizing a polarization-sensitive imager, this introduces polarization artifacts into the RSR curve. We present a simple method to avoid these polarization artifacts for division-of-focal-plane polarization imagers by directly illuminating the camera with the monochromator output and calculating the S0 Stokes parameter at each super pixel, then we show consistent results from this method for two division-of-focal-plane polarization imagers. We also show that ignoring the monochromator polarization results in order-of-magnitude RSR errors. The recommended method uses an iris to limit the spatial extent of the monochromator output, which was found experimentally to increase the minimum signal-to-noise ratio by more than a factor of 2.