Measurement Of Sound Velocity In The Water Based On The Stimulated Brillouin Scattering

Stimulated Brillouin scattering (SBS) as an important subject of non-linear optics,not only in theory and basic experimental research, but also in applied research areattracted people’s interest widely, and have done a lot of work on it. In this paper, wemainly revolves two important parameters of stimulated Brillouin scattering, frequencyshift and line width, to research the application of parameter measurement in water.On the one hand, we research the relation between the Stimulated Brillouinfrequency shift and the sound velocity. On the basis of theoretical analysis, wemeasured the Brillouin scattering frequency shift in the pure water and theconcentration of35‰brine through experiment, respectively, then calculation thesound velocity in the water by the frequency shift, then analyze the influence ofsalinity and temperature to the measure of frequency shift and sound velocity. On theother hand, line width as another important parameter for research sea parameters andmarine monitoring. In order to measure line width, we have proposed a new method bytime domain Fourier transform of pulse width in this paper. We have researched thecorrelation between SBS line width and pulse width at the temperature range from5to40℃. We obtainedSBS line width at different temperature by measured the SBS pulsewidth with Fourier transform and error correction at different temperature.The laser we used in the experiment is an injection-seeded Nd:YAG laser which isworking at the wavelength of532nm. The pure water we used is the distilled water andthe attenuation coefficient is about0.06/m, the salt water is the simulated seawater andthe concentration of35‰. The results of experiment show that, the measurements ofsound velocity is approach to the theoretical value, and can meet to the requirements ofactual measurements. The maximum error of sound velocity in pure water is about1.7m/s, the maximum relative error is about0.13%. The maximum error of soundvelocity in Salt water is about0.9m/s, the maximum relative error is about0.06%. Themaximum relative error of line width calculated by Fourier transform is less than3.5%.