Bicircular Attoclock with Molecules

在这个理论项目中，我们研究了在阿秒时间尺度上双原子分子中电子的动力学。我们使用一种特别定制的强光形式，称为双环场，它是两个不同颜色的反向旋转圆偏振激光场的叠加。求解含时薛定谔方程，计算了分子在双环场作用下电离产生的光电子动量分布。从这些结果中，我们推断阿秒尺度的强场电离的时间演化的信息（因此命名为attocock）和它的依赖于分子取向。动量分布中最大值的位置提供了关于出射电子的轨迹的信息。这样，原子钟就像一把纳米尺，可以检索电子的出生位置和势的渐近形状。通过分析具有可变延迟的附加探测场的响应，得到了特定动量的电离时间。与先前使用具有近圆偏振的光的时钟方案相比，双环场具有期望的性质，即它可以被定制，使得电离场方向在电子逃逸期间几乎恒定。这个场避免了复杂的问题，如电子轨迹的再散射或干扰。为了分析和解释数值计算的动量，分布，我们使用基于牛顿电子轨迹的模型。特别地，我们将经典的反向传播方法从原子扩展到分子。此外，我们使用一个无偏的，纯量子力学的方法来找到电离时间从含时薛定谔方程的积分表示。

In this theory project, we investigate the dynamics of electrons in diatomic molecules on the attosecond time scale. We use a specially tailored form of intense light, known as a bicircular field, which is a superposition of two counter-rotating circularly polarized laser fields of different colors. The time-dependent Schrödinger equation is solved to calculate the photoelectron momentum distributions resulting from ionization of molecules by bicircular fields. From these results we infer information about the attosecond-scale temporal evolution of strong-field ionization (hence the name attoclock) and its dependence on the molecular orientation. The location of the maximum in the momentum distribution provides information about the trajectory of the outgoing electron. In this way, the attoclock serves as a nano-ruler to retrieve the birth position of the electron and the asymptotic shape of the potential. The ionization time for a specified momentum is obtained by analyzing the response to an additional probe field with variable delay. In contrast to previous attoclock schemes using light with near-circular polarization, the bicircular field has the desirable property that it can be tailored such that the ionizing-field direction is nearly constant during the escape of the electron. Moreover, in contrast to conventional linear polarization, this field avoids complications such as rescattering or interference of electron trajectories.To analyze and interpret the numerically calculated momentum distributions, we use models based on Newtonian electron trajectories. In particular, we extend the classical backpropagation method from atoms to molecules. Furthermore, we use a trajectory-free, purely quantum-mechanical method to find the ionization time from an integral representation of the time-dependent Schrödinger equation.