激光脉冲诱导的等离子体密度调制及其产生的相位反射

理论研究和数值模拟发现入射光和反射光在低密度等离子体中形成的干涉场可以产生深度的等离子体密度调制. 对于中等强度的入射光，譬如10¹⁵W／cm² ，产生密度调制的时间尺度在几十个光周期的范围. 这样的等离子体密度调制可以起类似布拉格反射镜的 作用，使得后面的入射光在临界面以下的区域产生相位反射. 因为密度调制的周期是光在等 离子体中波长的一半，其产生的反射率可以接近100％. 相位反射也可以在不均匀的低密度 等离子体中产生，它可以极大地减少等离子体对光的吸收，因此在惯性约束核聚变中需要考 虑到它的影响. 关键词： 相位反射 密度调制 激光等离子体 粒子模拟

Density modulation produced by ultrashort laser pulses and the phase reflection induced in underdense plasmas

It is shown theoretically and by particle-in-cell simulations that the interfering fields of the incident and reflected laser pulses can produce deep plasma density modulations in underdense pre-plasmas. This occurs within a few tens of laser cycles if the incident laser pulse is at moderate intensities such as 10^15W/cm^2. Such density modulations can serve as a Bragg reflector, which results in phase reflection from underdense plasmas. Because the deep density modulations are just a period of half a wavelength in the plasma,the reflected wave reaches the maximum by resonance with a reflectivity up to near 100% .The phase reflection can also be observed from the plasma with a linear density profile, which can significantly reduce the laser absorption by fusion targets.