散斑场的随机波数及其参量非线性效应  

Random wavenumber and nonlinear parametric effect of speckle field

作　　者：杨春林[1] Yang Chun-Lin(Laser Fusion Research Center,China Academy of Engineering Physics,Mianyang 621900,China)

机构地区：[1]中国工程物理研究院激光聚变研究中心,绵阳621900

出　　处：《物理学报》2024年第2期175-180,共6页Acta Physica Sinica

摘　　要：散斑光场在非线性领域有特别的作用,它可用于抑制强光条件下的非线性过程.为了深入了解散斑的参量非线性作用机制,引入了具有波数失配的耦合波方程,讨论了方程的解,波数或位相匹配条件,波数不完全匹配时的增益阈值条件,以及完整解的待定系数.待定系数由边界场决定,如果边界的三个非线性波的复振幅都不为零,还存在边界位相匹配条件,满足该条件的待定系数最大.散斑光场的波数随机起伏,需要分段处理,这种波数随机起伏还会破坏边界位相匹配条件,从而抑制非线性增益.理论研究和数值计算的结果一致表明了散斑对受激布里渊散射参量过程的抑制作用.Speckle field is a relatively common phenomenon.But the speckle has special application value in nonlinear optical domain because it can be used to suppress different nonlinear processes that are caused by high power laser.To enhance the suppression capability,it is necessary to reveal the basic mechanism of the speckle parameter nonlinear optical interaction process.In this work,the coupling wave equation under the wave number mismatch condition is used to analyze the parameter process of speckles field.The solving process of the coupling wave equation is introduced in detail.And the wave number or phase matching condition is fully discussed.Furthermore,the threshold of the nonlinear gain is analyzed when the wave number does not fully meet the matching condition.To describe the solution of the coupling wave equation more clearly,the undetermined coefficient of the exact analytical solution is discussed.Since the boundary field will affect the confirmation of the undetermined coefficient,the characteristic of boundary field should be analyzed first.The nonlinear process of the speckle field is a three-wave interaction process.The different boundary conditions will affect the three-wave interaction process.And it is found that if the complex amplitudes of the three waves at the boundary are not zero,the undetermined coefficient will be changed with the phrase parameters of the three waves.To achieve the maximum value,the boundary waves must meet the phase matching condition.The wave number of the speckle filed is not an invariant,because of its random distribution characteristic.Therefore,during the analysis of the three-wave interaction process,the segment handling method is used to ensure the effective solving of the first order coupling wave equation.On the other hand,the randomly fluctuation of the wave number destroys the phase matching condition of the boundary.It is just through the basic mechanism that the speckle field can be used to suppress the nonlinear gain of high-power optical field.Both the theore

关 键 词：散斑 参量过程 位相匹配 

分 类 号：O437[机械工程—光学工程]