Momentum distributions from bichromatic ionization of atoms and molecules

从理论上研究了原子和分子对两种颜色组成的强激光脉冲的响应。在该项目的一个部分中，两种颜色在垂直方向上都被线极化，以探索由具有弱二次谐波场的基场所引起的电离动力学。在另一部分中，我们选择了圆极化和反旋转两种颜色，以探索在这样的双圆场中从电离时间到最终电子动量的不寻常映射。近年来，双圆场在高次谐波产生领域引起了人们的广泛关注，但光电子动量分布仍未得到很好的研究。用含时薛定谔方程的数值解计算了电子的动量分布，以捕捉电子的直接轨迹和再散射轨迹。并与强场近似作了比较。在原子中，应用双圆场研究亚周期电离动力学类似于ATTOCLOCK方法。在分子中，我们分析了与强场过程相关的量的取向关系，如电离时间和动量分布的横向宽度。在双圆场中分子的再散射电子信号中，我们寻找电子衍射的特征，以进行分子结构的超快成像。

The response of atoms and molecules to intense laser pulses composed of two colours is investigated theoretically. In one part of the project, both colours are linearly polarized in orthogonal directions in order to probe the ionization dynamics induced by the fundamental field with a weak second harmonic field. In the other part, we choose both colours circularly polarized and counter-rotating in order to exploit the unusual mapping from ionization times to final electron momenta in such bicircular fields. Bircircular fields have recently found remarkable attention in the area of high-harmonic generation, but the photoelectron momentum distributions remained mostly unexplored. The momentum distributions are calculated by numerical solution of the time-dependent Schrödinger equation in order to capture both the direct and the rescattering electron trajectories. Comparisons are made with the strong-field approximation. In atoms, application of bicircular fields for the study of sub-cycle ionization dynamics is envisaged analogous to the attoclock method. In molecules, we analyse the orientation dependence of quantities relevant for strong-field processes such as ionization times and the lateral width of the momentum distributions. In the rescattering electron signal from molecules in bicircular fields, we search for the signature of electron diffraction to perform ultrafast imaging of molecular structure.