半周期波形调控产生超宽谐波光谱平台区

Half-cycle waveform control for generating ultra-wide harmonic spectral plateau

为了获得高强度超宽谐波光谱平台区,采用数值求解含时薛定谔方程的方法,提出利用多色组合场调控半周期波形来获得最佳半周期谐波辐射条件。结果表明,通过调节双色场啁啾参量可以获得最佳的负向半周期波形;通过调节啁啾延迟可以获得最佳的正向半周期波形;在上述波形下,谐波截止能量得到延伸;引入紫外激光场后,在紫外共振增强电离的影响下,可以使谐波强度得到增强;当紫外光能量满足单、双光子共振增强电离时,谐波强度增强明显;随着紫外光子能量减小,谐波强度增强效果减弱;通过叠加谐波平台区谐波还可获得脉宽在50as以下的单个脉冲。这一结果对高次谐波调控以及阿秒脉冲产生是有帮助的。

In order to obtain intense and broad harmonic spectral plateau,by numerical solution of time-dependent Schrödinger equation,the half-cycle waveform control for producing the optimal half-cycle harmonic emission conditions was proposed by using multi-color combined field.The results show that,by controlling the chirps of two-color field,the optimal negative half-cycle waveform can be obtained;while,by controlling the chirp delay,the optimal positive half-cycle waveform can be produced.Driven by the above waveforms,the harmonic cutoffs can be extended.Further,with the introduction of ultraviolet pulse,due to the ultraviolet resonance enhanced ionization,the harmonic intensity can be enhanced.Furthermore,when the ultraviolet energy meets the single and two photon resonance enhanced ionization,the harmonic intensity is remarkably enhanced.With the decrease of ultraviolet photon energy,the enhancement of harmonic intensity decreases.Finally,the single attosecond pulses of sub-50as can be obtained by superposing harmonics on the harmonic spectral plateau.The results are helpful for the control of high-order harmonic generation and the production of attosecond pulses.