Davin Mao

Date of Award

3-22-2019

Document Type

Thesis

Degree Name

Master of Science in Applied Physics

Department

Department of Engineering Physics

First Advisor

Glen P. Perram, PhD

Abstract

Digital holography (DH) has been demonstrated to be an effective tool for tactical applications which involve in low signal-to-noise ratios (SNR). In practice, DH uses a strong reference beam from a local oscillator (LO) to scale SNR, however since DH relies on the interference of a signal beam with a mutually coherent LO, the coherence properties of the master oscillator (MO) can degrade system SNR for long range engagements. In this thesis, a digital holography system in the off-axis image plane recording geometry was assembled and used to measure the effects of the coherence properties of the MO on SNR. The coherence properties of the MO were degraded using sinusoidal phase modulation that imparted maximum phase shifts of 0.38π, 0.55π, and 0.73π at modulation frequencies of 20 MHz to 100 MHz. A relative visibility-squared model was developed and used to predict the the measured efficiency losses. Predictions were computed both from the modulator specifications, and from measurements taken using a Fabry-Perot interferometer, and at best the measurements deviated from the predictions by root-mean-square errors of 0.0378, 0.0373, and 0.391 for depths of modulation 0.38π, 0.55π, and 0.73π, respectively. Coherence efficiencies were measured at baseline SNRs of 75, 100, and 125 at the greatest depth of modulation, and it was found that the system’s baseline SNR did not significantly impact the coherence efficiency in the high SNR regime. Overall, the empirical data and models presented in this work may be used to assess efficiency losses in a DH system due to coherence effects.

AFIT Designator

AFIT-ENP-MS-19-M-084

DTIC Accession Number

AD1078185

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