对超短超强激光脉冲(45 fs,6×1017 W/cm2)与光致电离氦气形成的欠稠密等离子体相互作用中的二次谐波辐射进行了实验研究.测量了多种打靶强度的飞秒激光脉冲与不同气体密度氦气相互作用的二次谐波光谱,得到在欠稠密等离子体中二次谐波辐射与打靶激光能量的关系,分析了产生二次谐波辐射产生的物理机制,在考虑了强短脉冲激光电离气体产生的等离子体径向电子密度梯度因素,基于非线性作用过程的理论预期曲线与实验结果较好地吻合.

The experimental results of the second harmonic emission (SHE) in an ultrashort (45fs, 6×10 17 W/cm 2) laser pulse interaction with underdense plasmas formed from an optically ionized helium gas are presented. The spectra of SHE are measured under different intensities of fs laser pulses and the gas densities. The relationship between the conversion efficiency of SHE and the laser energy is studied. The theoretical explanation is given to the origin of SHE in underdense plasma. In consideration of the radial electron density gradient in plasmas produced by the intense ultrashort pulses propagation in the gas, a good agreement is obtained between experimental results and theoretical curve based on the nonlinear process.