激光的组合场相对相位对CO分子产生阿秒脉冲的影响

Influence of Relative Carrier Envelope Phases on Attosecond Pulse Generation from CO Molecule Exposed to a Combined Field of Lasers

利用强场近似方法研究了CO分子在组合场中发射高次谐波和阿秒脉冲的性质,组合场由波长为800nm和2000nm的两束激光形成。考虑了分子在组合场中的线性Stark位移对CO分子能级的影响,通过优化组合场的相对载波相位驱动分子。研究表明CO分子在这种组合场中不仅高次谐波的截止位置有了扩展,并且由于这种不对称分子在某一方向的电离抑制,减少了电子在演化过程的干涉效应,由此得到的高次谐波有很好的超连续性。叠加平台区域的高次谐波均能得到单个阿秒脉冲,脉冲宽度最窄可达到98as,与单色对称场驱动CO分子产生的阿秒脉冲相比较,其脉冲宽度有了明显的缩短。

We theoretically study the high-order harmonic generation and attosecond pulse generation of CO molecule exposed to a two-color combined field composed of 800 nm and 2000 nm laser pulses based on the strong field approximation, where the effect of linear Stark shift on molecular energy levels is considered. The two-color combined field can be efficiently controlled by optimizing their relative carrier envelope phases. The results show that the cut-off of harmonics is significantly extended in the combined field, and the supercontinuum of harmonics is apparently improved due to the ionization suppression of asymmetric molecule in a certain direction, which leads to the decrease of quantum interference during the propagation of the continuum electron. By superimposing several harmonics of the plateau region, the isolated attosecond pulse can be obtained for several relative phases, and the shortest pulse achieves 98 as. The width of attosecond pulse is obviously shortened compared with the situation that CO molecule is driven by a one-color laser field.