Combination of temporal phase unwrapping and long-wave infrared digital holographic interferometry for metrology of mosaic detector under space simulated conditions

We present digital holographic interferometry (DHI) in the long-wave infrared for monitoring the deformation under cryogenic conditions of a segmented focal plane array to be used in a space mission. The long wavelength was chosen for its ability to allow measurement of displacements 20 times larger than DHI in the visible and which were foreseen with the test object under such temperature changes. The specimen consists of 4x4 mosaic of detectors assembled on a frame. It was required to assess the global deformation of the ensemble, the deformation of each detector, and piston movements of each of them with respect to their neighbors. For that reason we incorporated the temporal phase unwrapping by capturing a sufficiently high number of holograms between which the phase does not suffer strong variations. At last since the specimen exhibit specular reflectivity at that wavelength, it is illuminated through a reflective diffuse