Detection of polarimetric signatures using high-efficiency polarimetric imaging techniques.

摘要

This research involved the development of a polarimetric imaging algorithm used for selective detection of back scattered photons transmitted through a medium. The novelty of the algorithm was the use of Stokes parameters and Mueller matrix methods to enhance turbid media imaging. This in turn may replace time-gated imaging, optical heterodyne, and second-harmonic generation techniques.; The first part consisted of exploring polarimetric phenomenology of 1-D and 2-D signals in a variety of experimental scenarios. Corner cube reflectors and arrays, photodiode windows, and camera zoom lenses were used as targets. Their polarization signatures, mainly reflected signal, optical cross section, line spread function (LSF) and modulation transfer function (MTF), were studied by applying Mueller matrix formalism.; The second part consisted of exploring the applicability of multi-fusional multi-spectral active imaging principles. This was aimed at enhancing image quality under different harsh imaging conditions using arithmetic manipulations of images at more than one wavelength. Aluminum strips, bar patterns, and computer chips were used as underwater targets and interrogated with more than one wavelength of laser. The images were analyzed using the Mueller matrix formalism. The resulting polarized images, and multi-wavelength subtraction images, were studied for contrast differences.; As a result of the study, we noted a few improvements. There was a visible increase in signal level when applying the degree of linear polarization (DOLP) algorithm. Since significant results were established using polarimetric signals, the polarimetric algorithm was used to test the impact on the size of a target's cross section. Using the range equation, we were able to improve the back scattered cross section of a corner cube and a camera zoom lens. DOLP was also able to improve the contrast of images taken with the lens focused, blurry, and out of focus. Similar results were observed for the LSF and MTF.; For underwater imaging, polarimetric intensities improved even though scattered intensities decreased with increasing water cloudiness. However, the increase was not uniform. When comparing images of two separate wavelengths, it was noted that the contrast of the DOLP images was not significantly better than the non-polarimetric images. The image of the first Stokes parameter of each wavelength managed to improve contrast two fold or better. The subtraction of back scattered images also improved contrast.