<title>Polarization-sensitive QWIP thermal imager</title>

Abstract

A polarization-sensitive thermal imager has been assembled using a quantum-well infrared photodetector (QWIP) focal plane array (FPA) with peak responsivity in the long-wave infrared (LWIR) spectral band near 9 µm. Polarization-dependent responsivity is achieved by etching linear gratings onto each pixel during QWIP FPA fabrication, with adjacent pixels having orthogonal grating orientation. The direct integration of the gratings with the pixels eliminates all pixel registration errors encountered with previous infrared polarimetry instruments. We present here details of the FPA and thermal imaging system design and performance and show examples of polarization-enhanced imagery. IntroductionExploitation of infrared polarization signatures can enhance the contrast of targets vs backgrounds. Targets are composed of man-made materials that tend to be smoother than natural materials, and hence both reflect and emit a stronger polarization signature than natural backgrounds.The development of polarization-sensitive infrared detectors is complex. Some previous efforts have employed rotating polarizers [1], polarization elements at an intermediate focal plane [2], and a polarization beam splitter producing two images on a single FPA [3]. The practical use of such instruments also involves added complexities [4]. Polarization analysis is very sensitive to misalignments, and precise six-axis alignment is difficult to achieve, verify, and maintain.We have designed and fabricated a focal-plane array (FPA) detector with polarization elements integrated onto each pixel, which eliminates the alignments and artifacts associated with separate polarization elements or multiple images. A description of the instrument and some preliminary characterization data is given below. Report Documentation Page

Breaking the Intersubband Selection Rules for Absorption with ZnO Quantum Wells: Light Polarization Sensitivity under Normal Incidence

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