为了研究超强激光与薄膜靶相互作用在入射光反射方向引起的高次谐波辐射, 基于在入射激光的透射方向,相干同步辐射机制会导致高次谐波的产生, 采用粒子模拟方法研究了超强激光驱动固体密度薄膜靶(即高密度薄膜靶)高次谐波辐射在入射激光透射和反射方向的空间分布。结果表明, 当靶厚小于激光趋肤深度、靶等离子体密度远大于临界密度(800Nc)时, 在透射方向,相干同步辐射机制会导致高次谐波辐射, 同时在反射方向,存在相对论镜面振荡机制驱动的谐波场辐射, 证明了在超强激光-薄膜靶相互作用过程中两种谐波会产生共存机制; 讨论了在两种产生机制下, 靶厚度对谐波辐射阶次的影响, 发现靶厚度超过200nm, 透射方向谐波阶次达到65阶以上。该研究对深入理解超强激光-薄膜靶驱动高次谐波的产生及阿秒X射线光源的未来发展具有一定的理论意义。

In order to study the higher order harmonic radiation induced by the interaction between super laser and thin foil targets in the reflection direction of incident light, the spatial distribution of high-order harmonic radiation of ultraintense laser-driven thin foil targets (high-density film targets) was investigated in the transmission and reflection direction of incident laser by using particle simulation method, because synchrotron radiation mechanism could lead to higher harmonic generation in the transmission direction of incident laser. The results show that, when the target thickness is less than the laser skin depth and the target plasma density is much larger than the critical density (800Nc), coherent synchrotron radiation can cause higher order radiation in the transmission direction. Harmonic field radiation is driven by relativistic mirror oscillation mechanism in the reflection direction. During the interaction between ultraintense laser and thin foil target, the coexistence of two harmonic generation mechanisms is proved. The influence of target thickness on the order of harmonic radiation was discussed under two kinds of production mechanism. The transmitted harmonics are more than 65 orders when target thickness exceeds 200nm. The study has some theoretical significance to research of high order harmonics generated by ultraintense laser-driven film targets and the future development of attosecond X-ray light sources.