AOTF Based Spectro-Polarimetric Imaging System for Stand-off Chemical Detection

Our goal in this SBIR project is to develop a lightweight, low-power, inexpensive hyperspectral spectro-polarimetric imaging sensor for wide area standoff detection of chemical agents. The imaging system will employ an acousto-optic tunable filter (AOTF) that operates in the LWIR wavelength range. The sensor will have polarimetric imaging capabilities which, adds a valuable signature feature to imaging data, allowing a wide variety of targets to be detected with greatly enhanced contrast. We investigated mercurous halides for the AOTF and developed techniques to grow large, high quality crystals and orient them for device fabrication. We developed suitable bonding techniques and successfully fabricated an AOTF with 25% diffraction efficiency at 10.6 um, the highest ever reported for a mercurous halide (to the best of our knowledge). We developed an optical design for the LWIR hyperspectral imager. Further improvements to the system include optimization of bonding to improve diffraction efficiency, development of seeded growth, which will optimize use of the grown crystals, and investigation of the ternary halide material mercurous bromo-iodide. The sensor will be able to passively detect small chemical plumes of chemical agents at relevant concentrations at a distance of 5 kilometers or more under ambient conditions.