Abstract: A nonlinear optical fluid with radiation-absorbing small particles uniformly suspended in the fluid. For radiation below a threshold value, radiation passes through with slight attenuation. Above the threshold, only a limited level of radiation is passed, the limit being below the damage level of a sensitive optical detector.

Abstract: A system for remotely sensing the velocity of sound in water using Brillouin scattering. A pulsed laser irradiates the water and the scattered light is collected, collimated and passed through a Fabry-Perot interferometer, then to a photomultiplier. The photomultiplier output is digitized. The interferometer is driven by a ramp generator, and the instantaneous voltage corresponds to the point in the frequency domain to which the digitized output corresponds. For each spectrum, a plurality of laser shots is obtained. A register contains the record of each shot, and when full its contents are transferred to a storage medium. A computer reads the storage medium and develops a three dimensional graphic representation the axes of which are frequency, intensity and depth.