The Theory Analysis Of Brillouin Scattering Dynamic Grating In Water And Related Technology Research

Stimulated Brillouin Scattering(SBS) has received general attention owing to itscharacteristics such as pulse compression, the phase conjugate and high energyreflectivity.The Brillouin sound field can be seen as a grating structure becauseStimulated Brillouin Scattering effect can produce periodic modulation of refractiveindex of medium. People can grasp a microscopic understanding of its scatteringmechanism by analyzing the refractive index modulation and the distributions ofultrasonic grating in the medium which produced Stimulated Brillouin Scattering(SBS).In this way,it is conductive to explain a series of Stimulated Brillouin Scattering(SBS)phenomenon on a theoretical level.Firstly, this paper has infered one-dimensional approximation to the coupledwave equation of Stimulated Brillouin Scattering in theory and have deduced formulaof the reflectivity of SBS. Then build the refractive index modulation model of thewater which includes Gauss-cosin refractive index modulation and non-uniformrefractive index modulation.This paper also has analyzed and discussed the factorsaffecting grating period and built the model of non-uniform period acousticgrating.The transfer matrix method is developed with the theory of multilayerdielectric film to numerical simulation of reflectance spectrum of Stimulated BrillouinScattering.Secondly, this paper has introduced the dynamic acoustic grating structure of thewater medium caused by Stimulated Brillouin Scattering phenomenon, including thelength of acoustic grating, the period of acoustic and other parameters. The SBSspectrum is simulated by the transfer matrix method based on the theory of multilayerdielectric film. The SBS spectrum for the hyper-acoustic grating we get is for aincident laser pulse’s wavelength of532nm, and in this paper has analyzes theinfluence of acoustic grating length and refractive index modulation depth and linearvariation coefficient of period on the efficiency of Stimulated Brillouin Scatteringspectrum peak. The stimulation results indicate that the greater the depth of refractiveindex modulation and the higher the spectrum peak efficiency of SBS, the wider thebandwidth of the reflection spectrum. It is also find that when the acoustic grating length L increased, the reflection efficiency of Stimulated Brillouin Scatteringincreased gradually, and the reflectivity increased dramatically and then became stablegradually when L reached centimeter magnitude. For a certain length of hyper-acousticgrating, the greater the reflection efficiency, the greater the bandwidth.The main peakof the spectral reflectance is bifurcated and the wavelength of the peak isredshift,caused by the increase of periodic linear variation coefficient.