Stokes Shapes Trait Disquisition Of Stimulated Brillouin Scattering

Stimulated Brillouin scattering (SBS) is an important means to achieve optical phase conjugation beam, which has the characteristics of self-pumping, producing phase conjugation wave. The dissertation is based on stimulated Brillouin scattering (SBS) phase conjugation technology, integrating with light(wavelength 532ns) pulse laser system which has high transmission radio in ocean.Based on stimulated Brillouin scattering(SBS), we put forward method of detecting object underwater. By analyzing Stokes pulse portrait of SBS in the ocean, we give the feasibility of submarine object detection by SBS. The dissertation has important science meaning in developing theory and practicality of SBS.First, based on coupled wave equations of interaction between pump field, Stokes field, acoustic field in SBS process, theoretical model of stimulated Brillouin scattering including noise initiation is constructed, and then physical models of one-cell SBS for numerical simulation are built up. Using an implicit finite differencing in time and a down-wind differencing scheme in space, theoretical calculation models of SBS for numerical simulations are built up, numerical calculation programs for simulating SBS pulse shapes of one-cell are made.On the basis of theoretical calculation models of SBS,five parameters which characterize Stokes portrait in SBS process are defined as follows: peak power reflectivity; separation between peaks; peak power ratio; modulation depth; leading edge.Transit numerical simulation and theory analyse Stokes shape change rule in water, Relationships of all above parameters on configuration parameters (focusing length, cell length),pump parameters (input peak power , pulse duration), medium parameters (gain, phonon life time) are analyzed, and discuss deep-seated physics reasons. By investigating Stokes pulse portrait in stimulated Brillouin scattering process,we discovered by increasing cell length and pump pulse duration, choosing SBS medium with proper focus , upper pump energy and gain coefficient, short lifetime, then we can gain high signal and fast response characteristics.On the basis of theoretical calculation models of SBS, we introduce fiber simulate Brillouin Scattering to ocean. Four parameters which characterize Stokes portrait in SBS process are defined as follows: peak power reflectivity; pulse compression; modulation depth; leading edge. By studing of Stokes pulse portrait in SBS of fiber,we found by increasing pump pulse duration and energy, choosing SBS fiber medium with large gain coefficient, and choosing short lifetime, we can be conveniently give high signal and good response characteristics.The dissertation of Stokes por trait performs in stimulated Brillouin scattering process gives theoretical direction for the application of SBS in submarine object detection.