Theory of Molecular Quantum Dynamics in High-Harmonic Generation

高谐波产生，即通过激光照射原子或分子产生高频光子，目前正在进行大量的研究工作。在被广泛接受的三步模型中，谐波辐射起源于电离、电子在激光场中的自由加速和与磁芯的重新结合的一系列过程。这种回忆是非常有趣的，因为它允许用它自己的电子探测分子的状态。以前，分子动力学对高次谐波产生的影响是在一个近似的情况下描述的，其中只有活性电子感受到激光力，而核心的动力学是场自由的。在这里，我们发展了一种理论来克服这一限制，并考虑到分子核与激光场的相互作用。这涉及到核波包在激光耦合玻恩-奥本海默表面的传播。这种方法既适用于双原子分子，也适用于多原子分子。由核运动引起的谐波谱中的特征包含了激光诱导的玻恩-奥本海默势的瞬时畸变信息，从而提供了一种实验研究这些畸变的方法。我们研究了利用核运动控制高次谐波产生的方案。不仅对通常的钛蓝宝石激光波长进行谐波光谱预测，而且还计划对更长的红外波长进行谐波光谱预测。

Intensive research efforts are currently devoted to high-harmonic generation, i.e. the generation of high-frequency photons by laser irradiation of atoms or molecules. In the widely accepted three-step model, harmonic radiation originates from a sequence of ionization, free acceleration of the electron in the laser field, and recollision with the core. This recollision is of great interest since it allows to probe the state of a molecule with its own electron. Previously, the influence of molecular dynamics on high-harmonic generation was described in an approximation where only the active electron feels the laser force while the dynamics of the core is field free. Here, we develop a theory to overcome this limitation and take the interaction of the molecular core with the laser field into account. This involves the propagation of nuclear wave packets in laser-coupled Born-Oppenheimer surfaces. The approach is applicable to diatomic as well as polyatomic molecules. The signatures in the harmonic spectrum due to nuclear motion contain information on the instantaneous laser-induced distortion of Born-Oppenheimer potentials, thus providing a way to investigate these distortions experimentally. We investigate schemes to control high harmonic generation by exploiting the nuclear motion. Predictions of harmonic spectra not only for the usual Ti:Sapphire laser wavelength but also for longer infrared wavelengths are planned.