Investigation On Stimulated Brillouin Scattering Self-phase Control For Coherent Beam Conbination With Independent Cell Configuration

Using stimulated Brillouin scattering to lock the phase relations between the beams,then to obtain the beam combination, is a promising method for the high energy outputwith a high repetition rate in many applications, such as those in high energy densityphysics, laboratory astrophysics, especially a basic research of inertial fusion, bysolving fundamental thermal problems, compensating the distortion generated duringamplification, and working at10Hz.What is a very important factor is that the phase relations between the sub beamsshould be locked. A destiny modulation to Brillouin medium can be obtained byintroducing a reference light, which can control Stocks phase. This paper aims toinvestigation on the mechanism of controlling Stocks phase by the self-generateddensity modulation.The coupled wave equations of stimulated Brillouin scattering in general rule arederived according to Maxwell equations and Navier-Stokes equations; and thenconsidered the density modulation, the coupled wave equations including self-generateddensity modulation are also derived. So the self-generated density modulation theorymodel and its numerical equation are established.A method of implicit finite difference in time and backward difference in space isused to solve the obtained equation numerically, and the dependence of phase stabilityof Stocks beam on parameters of pump beam, medium and structure of independent cellis computed numerically by the theoretical model, by computing initial position ofStocks and analyzing relationship between Stocks position and Stocks phase, then anoptimum operating parameter of stimulated Brillouin scattering self-phase control bydensity modulation is obtained, including factors of waveform of Stocks and energyreflectivity of stimulated Brillouin scattering.Analysing the demand of balancing the energies between beams on differentthresholds theoretically, a independent cell configuration to control Stocks phase ismade out, and an optical system is designed and built, with low threshold by lens andtwo sub beams by amplitude dividing scheme. Phase stabilities on different thresholds isobtained experimentally, and the ideal threshold operating point is finally determined.