Simulation study on harmonic radiation of ultraintense laser-driven thin foil targets

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 (800N_c), 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.