Date of Award

6-1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Engineering Physics

First Advisor

Michael C. Roggemann, PhD

Abstract

In sheared coherent beam interferometric imaging, an estimate of the average reflectivity profile of the object can be computed from measurements of point to point phase differences in the far field interference pattern and a suitable phase reconstruction technique. The phase difference information is encoded in the irradiance of three identical, shifted and superimposed speckled laser beam patterns. A minimum variance phase reconstruction technique is presented to estimate the phase of the field in the measurement plane from the phase differences and evaluate its performance. Prior knowledge of the phase covariance is used in the minimum variance reconstructor. Analytic calculations and computer simulations are used to evaluate phase reconstruction errors as a function of object coherence area and spatial sample spacing in the measurement plane. The performance of the minimum variance reconstructor is compared to two least squares reconstructor implementations. Theoretical performance comparisons are made between the minimum variance reconstructor and a new implementation of the least squares formalism. The new least squares reconstructor uses the same error metric as the minimum variance reconstructor but does not use any statistical information in estimating the measurement plane phase function. Comparisons of the minimum variance reconstructor with a conventional implementation of the least squares formalism are also made. The performance of the minimum variance reconstructor is demonstrated for objects which are optically smooth as well as optically rough. A small random double point source object is used to demonstrate the near diffraction limited resolution of the minimum variance wavefront reconstructor.

AFIT Designator

AFIT-DS-ENP-95-J

DTIC Accession Number

ADA297541

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