Acousto-optic tunable filter based spectropolarimetric imagers

Development of robust compact spectropolarimetric imagers that can acquire spectral, spatial and polarization features from a scene of interest is of utmost importance for efficient detection of targets and backgrounds. Spectral features arise due to the material properties of objects as a result of the emission, reflection, and absorption of light while the polarization features arise from the physical nature of the object surfaces and edges that influence the polarization properties of the reflected, scattered, or emitted light. Using a hyperspectral imager one can acquire images with narrow spectral bands and take advantage of the characteristic spectral signatures of different materials making up objects and backgrounds. By combining both polarization and hyperspectral detection capabilities in one single imager, we can perform much better object detection and identification than by using either polarization or hyperspectral detection capability. Spectropolarimetrc imagers designed using an acousto-optic tunable filter (AOTF) are ideally suited to provide both agile spectral and polarization signatures. At the U.S. Army Research Laboratory (ARL), we are developing small, vibration-insensitive, robust, remotely controlled, and programmable hyperspectral imagers from the ultraviolet to the long wave infrared. We have also demonstrated a full Stokes polarization imager using an AOTF with two liquid crystal retarders. Here, we will discuss our imager designs and present results from our experiments.