White light channeled imaging polarimeter using broadband polarization gratings

Abstract: A white-light snapshot channeled linear imaging (CLI) polarimeter is demonstrated by utilizing polarization gratings (PGs). The CLI is capable of measuring the 2-dimensional distribution of the linear Stokes polarization parameters corresponding to S0, S1 and S2 by incorporating two identical PGs, in series along the optical axis. In this configuration, the general optical shearing functionality of a uniaxial crystal-based Savart plate is realized. However, unlike a Savart plate, the diffractive nature of the PGs creates a linear dependence of the shear versus wavelength, thus providing broadband functionality. The concept is also theoretically demonstrated to be capable of measuring the complete Stokes vector (S0, S1, S2 and S3) in white light. Consequently, by incorporating the PG-based Savart plate into a Savart plate channeled imaging polarimeter, white-light interference fringes can be generated. This enables polarimetric image data to be acquired at shorter exposure times in daylight conditions, making it more appealing for snapshot remote sensing applications versus previously described quasi-monochromatic instruments. Furthermore, the PG-based device offers significantly more compactness, field of view, optical simplicity and vibration insensitivity than previously published white-light channeled linear imaging polarimeter implementations. Included in this paper are theoretical descriptions for both the linear and complete Stokes imaging polarimeters. Additionally, descriptions of our calibration procedures and our experimental proof of concept CLI system are provided. These are followed by laboratory and outdoor polarimetric measurements of S0, S1 and S2.