采用单电子模型研究了圆偏振飞秒脉冲激光作用下电子振荡导致的谐波辐射频谱的特性.研究发现随着激光强度的增加,电子在激光场中运动的相对论效应可以导致谐波辐射,并且发现谐波辐射频谱随着激光强度的增加发生了展宽和红移.电子与强激光脉冲相互作用,电子除了在激光场的作用下做横向振荡运动之外,激光脉冲的纵向有质动力对电子还有推动作用,这是产生谐波频谱红移的原因,而谐波辐射频谱展宽是由电子纵向速度的变化引起的.分析激光场中电子在不同方向的辐射频谱表明:随着谐波阶数的升高,红移在有规律地变大;在θ＝3π/4方向上电子频谱的红移比θ＝π/2方向上更明显.

The characteristics of spectral distribution of harmonic emission are analyzed with a single electron model in the cases of circularly polarized femtosecond laser pulses.It is discovered that with the increase of laser intensity,the oscillation of electrons,due to their relativistic motion,will generate harmonic emission,the spectrum of harmonic emission is broadened and red shift occurs.The effects discussed in this paper may be used to explain the broaden and redshift of harmonic emission from plasma irradiated by femtosecond intense laser pulses.