最近的理论和实验研究表明，相对论强激光与固体靶相互作用产生高次谐波辐射的方案可以突破与气体靶相互作用产生机制中对驱动激光强度的限制，有望产生能量更高、时间更短的相干脉冲辐射。这一过程中预等离子体密度标长对高次谐波产生效率及其时空特性都有重要影响。本项目拟在上海交通大学200太瓦飞秒激光装置上对相对论强激光脉冲与固体靶相互作用产生高次谐波的物理过程开展实验研究，发展相关的实验诊断测量技术，通过改变激光对比度和引入预脉冲两种方法控制靶面等离子体密度标长，研究其对高次谐波产生的影响，为将来提高产生效率，降低对驱动激光的要求等提供参考。

Recent theoretical and experimental results indicate that high oder harmonics generation by the interactions of relativistic laser with solid target could overcome the limit on laser intensity in the laser-gas interactions, so that it is potential to obtain coherent radiations with higher energy and shorter pulse duration. The preplama density scale length has great effect on the generation efficienty and temporal-spatial characteristics of high-order harmonics.The project expects to perform experimental studies on the high-order harmonics generation from relativistic laser pulses with plasmas using the 200 TW femtosecond laser facility at Shanghai Jiao Tong University. We propose to develop the diagnostic and detection techniques for the measurement of high order harmonics, and investigate the influence of plasma density scale length on the high-order generation process by changing the contrast of the laser pulse or using a prepulse,for improving the generation efficiency and decrease the technical demands on the driven lasers in the future .