双色激光场驱动原子产生太赫兹辐射相关电子动力学研究

The terahertz(THz) emission is simulated with the model of the residual current density (RCD) excitation in the interaction of the laser field and the atom. We can get the residual current, which is the initial impetus to plasma excitation of transverse dipole oscillationa with THz frequencies, by solving the time-dependent Schr?dinger equation. The THz intensity is proportional to the square of the RCD. Comparing to the direct calculation of THz emission spectrum based on the quantum calculation, this is still the ab initio model with the same veracity. While the calculation efficiency is enhanced a lot, because the pico-seconds interaction calculation, which is much longer than the duration of the laser pulse, is not necessary to get the coherent emission spectrum in THz precision. In the RCD model, the asymmetry of the velocity of the ionized electron is the key reason for the THz emission. We constrate on the dynamics of the electron in strong two-color laser field, which is a usual way to strengthen the THz emissions. The new physical phenomena and effects can be observed by adjusting the relative phase, intensity and the phase duration of the two-color laser fields. Besides, the THz emission dynamics can be connected to the other strong-filed phenomena such as the high-order harmonic generation (HHG) and above-threshold ionization (ATI) etc. This connection can enrich the electronic dynamical process in the strong laser field and help us decribe the electronic dynamics quantificationally.

本项目拟采用剩余电流密度模型对太赫兹辐射进行数值模拟，通过数值求解真实原子体系的含时薛定谔方程，对激光作用时间内电子的剩余电流，即等离子体以太赫兹频率震荡的初始动力，进行计算。太赫兹辐射强度正比于剩余电流密度的平方。与直接用量子模型计算太赫兹辐射谱相比，该方法不需要在程序中计算皮秒量级以获得太赫兹精度的相干辐射谱，在保证太赫兹辐射精确计算的基础上大大提高了计算效率。该模型中，太赫兹辐射正比于电离电子空间速度分布的不对称性，基于该机制，我们将着重研究电子在双色激光场中的动力学行为，改变激光相位、强度、脉宽等特征，观察新的物理现象和效应。并将太赫兹辐射与高次谐波、阈上电离等强场物理现象相联系，对其相应动力学行为进行定量描述并丰富强场中的电子的动力学图像。

现今，太赫兹成为观测和操控强场中电子动力学的新手段。本项目通过求解含时薛定谔的方法同时计算了双色场下太赫兹辐射，高次谐波以及阈上电离谱。首先结合实验上同步探测高次谐波以及太赫兹辐射的结果，我们发现太赫兹辐射会受到阿秒精度内动力学行为的调制，指出激光场的阿秒整型以及库仑势的存在会改变逃逸电流与重散射电流之间的比率以及双色场下太赫兹辐射的最优相位，并且该相位会随光强增加而减少，为太赫兹辐射相关的电子动力学行为给出了更加细致的光电流模型。接着，为了给出具体逃逸电流与重散射电流之间的比率变化，我们讨论了阈上电离谱的双平台强度的变化，进一步证实了我们给出的重散射动力学模型。这项工作首次将太赫兹辐射强度与阈上电离谱的左右不对称性相关联，该关联效应比高次谐波的更加直接，可为我们进一步研究太赫兹辐射相关动力学行为以及相干控制手段提供很大的帮助。