黑腔中空间束匀滑光束成丝不稳定性的数值模拟

Numerical simulation of filamentation for spatially smoothing beam in hohlraum

为深入研究黑腔内激光成丝不稳定性产生和发展,建立了空间束匀滑光束的传播模型,利用三维激光等离子体相互作用程序LAP3D模拟了黑腔物理条件下的大尺度成丝现象。模拟结果可正确描述成丝后光强的束发散现象及谱空间光强分布特征。从激光能量参数角度分析了导致成丝不稳定性发展的物理因素,并讨论了应用空间束匀滑技术抑制成丝不稳定性的局限性。研究表明:空间束匀滑光束发展成丝的能力取决于光斑内小焦斑的成丝表现,当具备成丝能力的小焦斑份额达到一定比例后,就会导致整个空间束匀滑光束成丝,因此对于光斑平均功率密度较高的光束,须考虑结合其他束匀滑手段来抑制成丝发展。

Three dimensional models of spatially smoothing beam propagating in hohlraum are established in a laser plasma simulation code named LAP3 Dto investigate laser filamentation.Simulation results of spatially smoothing beam produced by continuous phase plates（CPP）with a given fnumber（f=11）propagating in a 2000 laser wavelength long homogeneous slab plasma,corresponding to plasma density at tenth of the critical density,electron and ion temperature at 3and 1keV,respectively,are presented in this paper.The influence of parameters associated with the beam power and intensities on developing of laser filamentation instability is analyzed.Features of laser filamentation instability are found with simulation results,including beam spay and laser energy spreading to higher wave numbers in the Fourier space.It is found that there is a clear correlation between onset of the beam filamentation and the value of the average laser intensity.Based on simulation results,it is suggested that with high hot spot intensities,bigger size hot spots or other smoothing methods should be applied to suppress laser filamentation.