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.

Study of condensed matter by optical techniques; inelastic light scattering spectroscopy; structure, optical properties and applications of liquid crystals; liquid crystal electro-optics; membrane biophysics; structure and dynamics of colloidal suspensions; nanometer scale fabrication; liquid structure and melting; soft matter chirality; liquid crystals of bent-core molecules; liquid crystals of DNA and RNA; liquid crystals and the origin of life; ferromagnetic liquid crystals.

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Formulas are derived for the roots of the dispersion equation for temporally damped hydrodynamic waves in a viscous, thermally conducting liquid having also a frequency-dependent viscosity with one or more relaxation times. Values of the roots are then computed for CCI. at 25°C for practically the entire range of wavenumbers, under the assumption that the extra viscosity has a relaxation time of 5.43 X 10-11 sec. Next, the values of the roots corresponding to k",,2X1()6 cm-I (for 90° scattering of He-Ne laser light) are used to calculate both the unbroadened and the instrumentally broadened Rayleigh-Brillouin spectrum. A similar calculation under the assumption that CCI. is doubly relaxing shows radically different velocity dispersion curves according to the relaxation time T2 assigned to the longitudinal viscosity. For T2= 10-18 sec, viscous overdamping reduces the sound velocity to zero for a narrow range of wavenumbers above about k = 1.2X 10 7 em-I. For n= 10-12 sec, the velocity is an increasing function of frequency with points of inflection at about 3 and 100 GHz, as anticipated for a process having two widely separated relaxation frequencies. whose molecules have internal degrees of freedom weakly coupled to their translational degrees by a process having a single relaxation time. 2 ,3 His explicit (and approximate) expression for the intensity spectrum of the scattered light predicts Brillouin peaks which are symmetric Loren tzians, apart from overlap with the central components.This symmetry has been verified frequently by 2 R. D. Mountain, J. Chern. Phys. 44, 832 (1966).