Comparison of different active polarimetric imaging modes for target detection in outdoor environment.

We address the detection of manufactured objects in different types of environments with active polarimetric imaging. Using an original, fully adaptive imager, we compare several imaging modes having different numbers of polarimetric degrees of freedom. We demonstrate the efficiency of active polarimetric imaging for decamouflage and hazardous object detection, and underline the characteristics that a polarimetric imager aimed at this type of application should possess. We show that in most encountered scenarios the Mueller matrices are nearly diagonal, and sufficient detection performance can be obtained with simple polarimetric imaging systems having reduced degrees of freedom. Moreover, intensity normalization of images is of paramount importance to better reveal polarimetric contrast.

Active polarimetric imager with near infrared laser illumination for adaptive contrast optimization.

We designed and built an active polarimetric imager with laser illumination at 1.5 µm wavelength for adaptive polarimetric contrast optimization. It can generate and analyze any polarization state on the Poincaré sphere in order to best adapt to the polarimetric properties of the scene. Polarimetric contrast optimization is performed by analyzing the scene with an ultrafast active-contour-based segmentation algorithm. This device is, to the best of our knowledge, the first fully adaptive imager controlled by image processing algorithms for polarimetric contrast enhancement. Its capabilities are illustrated in some examples of real-world decamouflage applications.

Coded aperture detector: an image sensor with sub 20-nm pixel resolution.

We describe the coded aperture detector, a novel image sensor based on uniformly redundant arrays (URAs) with customizable pixel size, resolution, and operating photon energy regime. In this sensor, a coded aperture is scanned laterally at the image plane of an optical system, and the transmitted intensity is measured by a photodiode. The image intensity is then digitally reconstructed using a simple convolution. We present results from a proof-of-principle optical prototype, demonstrating high-fidelity image sensing comparable to a CCD. A 20-nm half-pitch URA fabricated by the Center for X-ray Optics (CXRO) nano-fabrication laboratory is presented that is suitable for high-resolution image sensing at EUV and soft X-ray wavelengths.