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We have demonstrated the feasibility of employing directly acousto-optic interactions in an optical fiber to produce a sensitive acoustic detector. Our technique utilizes the phase modulation of an optical beam in a submerged optical fiber coil by sound waves propagating in a fluid. Analysis of our results indicates that the sensitivity of this technique compares well with that of the best available hydrophone.

Thermal Brillouin scattering has been studied in fused silica from room temperature, through the glass transition temperature (1200°C), and up to near the melting temperature of quartz (∼1700°C). The shear and longitudinal Brillouin shifts, the longitudinal linewidth, Pockel's coefficient, and the Landau-Placzek ratio are measured. From these the behavior of the elastic moduli and absorption coefficient with temperature are obtained. A significant change in the temperature dependence of the moduli and Pockel's coefficient is found to occur above 500°C. In addition, by using the Landau-Placzek ratio the first measurement in fused quartz of the equilibrium static compressibility above the glass transition has been obtained. Surprisingly little temperature dependence is observed.

From the measurement of the acoustic pressure on a cylindrical, two-dimensional contour located close to the surface of an underwater, vibrating cylinder, the complete three-dimensional sound field can be reproduced (reconstructed) with the aid of a computer. This reconstruction technique, called GENAH (generalized nearfield acoustical holography), is unlike conventional holography because it provides a super resolution image of the sound-pressure field from the surface of the cylinder to the farfield. At the same time, GENAH reconstructs, from this two-dimensional measurement, the vector velocity and the vector intensity fields (energy flow) in the nearfield of the source, and identifies modes of surface vibration of the cylinder. Experimental results are provided and the accuracy of GENAH is demonstrated by comparison with the two-hydrophone technique.

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