Three-dimensional strong acousto-optic interaction theory

Abstract

This dissertation presents two different three-dimensional theories that examine the interaction between light and "strong" sound fields. Strong refers to a sound field strength sufficient to deflect most of the incident light into the first diffracted order, but not strong enough to induce nonlinear behavior in the acousto-optic cell. Primary emphasis is placed on deriving and experimentally verifying theories that predict the interaction process. All strong interaction theories to date consider only two transverse dimensions, where sound and light travel predominantly in the x and z directions, respectively. Our theories employ "split-step" type numerical methods to solve the theoretical equations derived for the interaction. The first method is called the Fourier-Optics approach and applies directly to a nondiffracting sound column. An incident light beam propagates through the cell by alternating between interaction and diffraction. The second method is called the Wave-Equation approach because it solves the coupled differential equations derived from Maxwell's equations. This method differs from the Fourier-Optics approach because it includes sound field diffraction into the interaction process. Throughout both theories we assume the sound field represents a bulk acoustic wave. Theoretical predictions show and experimental measurements verify that adding the y dimension into the interaction process enables one to examine acousto-optic interaction effects in a different way. Specifically, we show that the height (measured along the y-direction) of the sound beam contributes to distortions of the zero diffracted order not predicted by other theories. We also show that the y-dimension contributes to a reduction in diffraction efficiency as the light beam is incident at greater distances away from the acoustic transducer. This effect while observed in practice has not been shown in theory by previous acousto-optic interaction theories. Both theoretical predictions and experimental results are presented below.