(Dr. Peter Rogers, advisor)

"Underwater Surface Displacement in the Presence of Underwater Sound Using LDV"

Abstract

Research conducted here at Georgia Tech in the area of sonar development has produced the desire for an LDV system capable of making measurements on a diffusely reflecting surface and in the presence of underwater sound.  Previous work done at Georgia Tech in the area of LDV development has shown that such as system must have several unique characteristics.  First, since measurements are being made in the presence of sound, the LDV probe must have a minimal acoustic presence.  In other words, it cannot significantly alter the acoustic field present.  Secondly, the system must be able to account for several sources of piezooptically induced modulation which would otherwise produce erroneous measurements.  Thirdly, since measurements are being made on a diffusely reflecting surface, the system must be able to operate on a very small amount of backreflected light.

The work done in completion of this thesis addressed these issues critical to the development of such an LDV system.  In particular, the work dealt with, one, the development of an optical system that could detect vibrations from an optically diffuse surface by sending and receiving light through one SMPM optical fiber.  Two, verifying that the optical probe of such a system would have a minimal acoustic presence in the water.  Three, examining piezooptic effects in SMPM fibers due to underwater acoustic fields along with the feasibility of eliminating these effects using common-mode rejection.