DIRS Laboratory 76-3215
August 23, 2019 at 10:00am
Jacob Wirth
Ph.D. Thesis Defense
Abstract: 

Abstract

 

A novel computational imaging approach to sensor protection based on point spread function (PSF) engineering is designed to suppress harmful laser irradiance without significant loss of image fidelity of a background scene. PSF engineering is accomplished by modifying a traditional imaging system with a lossless linear phase masks at the pupil which diffracts laser light over a large area of the imaging sensor. The approach provides the additional advantage of an instantaneous response time across a broad region of the electromagnetic spectrum. As the mask does not discriminate between the laser and desired scene, a post-processing image reconstruction step is required, which may be accomplished in real time, that both removes the laser spot and improves the image fidelity.

This thesis includes significant experimental and numerical advancements in the determination and demonstration of optimized phase masks. Analytic studies of PSF engineering systems and their fundamental limits were conducted. An experimental test-bed was designed using a spatial light modulator to create digitally-controlled phase masks to image a target in the presence of a laser source. Experimental results using already known phase masks: axicon, vortex and cubic are reported. New methods for designing phase masks are also reported including (1) a numeric differential evolution algorithm, (2) a “PSF reverse engineering” method, and (3) a hardware based simulated annealing experiment. Broadband performance of optimized phase masks were also evaluated in simulation. Optimized phase masks were shown to provide three orders of magnitude laser suppression while simultaneously providing high fidelity imaging a background scene.