氦原子在啁啾激光与中红外组合场中产生的单个阿秒脉冲

Single attosecond pulse generated by model helium atom exposed to the combined field of an intense chirped laser pulse and midinfrared laser pulse

通过Crank Nicolson方法数值求解一维氦原子的含时Schrdinger方程,研究了啁啾激光与中红外激光形成组合场驱动氦原子发射高次谐波的特点.研究结果表明,在组合场驱动下,高次谐波平台区能得到很大的扩展,其截至位置得到大幅度扩展,对平台区不同阶次范围的高次谐波进行叠加均能得到单个的阿秒脉冲,最短可实现46 as的单个脉冲输出,经分析发现,中红外场的加入,不仅使高次谐波的平台得到扩展,而且提高了平台区前端的谐波强度.通过经典计算和对电离几率特点的讨论,解释了发生这种现象的原因.

By solving numerically the time - dependent Schr6dinger equation with Crank - Nicolson method, we investigate characteristics of the high - harmonic generation of one - dimensional helium atom exposed to the combined field of the intense chirped laser and midinfrared laser pulse. It is shown that the cutoff of the harmonic spectrum is extended greatly in case of the combined fields, and we can get a group of isolated attosecond pulses by superimposing some high -order harmonics in the plateau, the minimum pulse achieves 46 attoseconds. By means of the analysis, we find that the adding midinfrared laser pulse can not only extend the plateau of high - harmonic spectrum, but also improve intensity of high- harmonic spectrum in the plateau front. We explain the reasons by classical analysis and discussion about characteristics of ionization probability.