Bicircular Attoclock with Molecules

在这个理论项目中，我们研究了双原子分子中电子在阿秒时间尺度上的动力学。我们使用一种特别定制的强光形式，称为双圆场，它是两个不同颜色的反向旋转的圆偏振激光场的叠加。通过求解含时薛定谔方程，计算了分子在双圆场中电离产生的光电子动量分布。根据这些结果，我们推断了强场电离的阿秒尺度时间演化信息(由此得名ATTOCLOCK)及其与分子取向的依赖关系。动量分布中最大值的位置提供了有关出射电子轨迹的信息。通过这种方式，钟表起到了纳米尺子的作用，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，得到了指定动量的电离时间。与以前使用近圆偏振光的时钟方案不同，双圆磁场具有所需的特性，即它可以被定制，使得在电子逃逸期间电离场方向几乎是恒定的。此外，与传统的线极化相比，该场避免了电子轨迹的重新散射或干扰等复杂情况。为了分析和解释数值计算的动量分布，我们使用了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，我们使用一种无轨迹的纯量子力学方法从含时薛定谔方程的积分表示中求出电离时间。

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.