Phase Retrieval with an Opacity Constraint in LAser IMaging (PROCLAIM)

Abstract

PROCLAIM is an active-illumination imaging method that utilizes flood illumination of an opaque object with a frequency-tunable laser [1,2,3]. The reflected radiation at a single frequency will create a speckle pattern in the far-field. The intensity of this far-field speckle pattern is directly detected with an array of detectors and without intervening optics. Typically, the illuminating laser will step through several frequencies so that a separate cross-range speckle intensity pattern is collected for each of multiple frequencies. Properly formatted, these data correspond to the modulus squared of the Fourier transform of the object’s 3-D complex reflectivity function [4]. If the object’s Fourier phase can be retrieved, then the Fourier representation of the object will be complete and a 3-D FFT could be used to recover the object’s 3-D complex reflectivity. Thus, phase-retrieval is an integral element of the PROCLAIM imaging modality. A schematic diagram of the data-collection and processing that constitute the PROCLAIM imaging modality is presented in Fig. 1.