<title>Design and construction of a four-channel 527-nm imaging polarimeter</title>

Abstract

A four channel imaging Stokes polarimeter has been designed and constructed at the Air Force Research Laboratories to measure the polarization properties of laser speckle patterns. An imaging polarimeter spatially measures the polarization state of light coming from an object, thereby producing a "polarization image". This provides a complete characterization, in terms of the 4 Stokes polarization parameters, of light received from different regions of an object. In addition to the intensity information obtained from conventional imagery, an imaging polarimeter also measures the two components of the electric field, and the phase between these components. This additional information has been shown in the laboratory to aid in the discrimination of otherwise similar looking materials. Due to the random phases present in unpolarized light, polarization images are most useful when the object being viewed is illuminated by a uniformly polarized light source, such as a simple laser illuminator. The system described was designed to image the pupil of an optical system containing speckle patterns created by illumination of diffuse objects with light from a pulsed 527 nm laser. Diagnostic techniques developed to measure path length differences between channels and various system calibration and characterization tests are described and results are presented.