Dressed states and adiabatic passage for high-intensity nonlinear optics

这一更新建议的目的是扩展我们之前对谐波产生的研究，通过原子多光子共振的相干-绝热相互作用增强。我们的特别目标是将在中等激光强度下建立的相干相互作用的概念转移到高强度非线性光学中。在我们的工作中，我们应用了盛装态和绝热过程。后者对实验参数的波动提供了鲁棒性，并且适用于仍然足够中等带宽的短激光脉冲，以选择性地驱动和利用原子共振。如果驱动激光场不超过原子中的库仑场，从而破坏或强烈改变能级结构，那么通过原子共振的相干-绝热控制方法就能很好地工作。另一方面，高效的非线性光学通常需要超快、高强度的激光脉冲。在这种情况下，能级结构和跃迁的光谱形状发生了很大的变化，例如，通过交流斯塔克位移，很容易达到每TW/cm²激光强度许多太赫兹。共振增强和绝热过程在这种高强度状态下的应用需要新的方法来处理交流电平移位。正如我们最近在（符号删除）中所展示的，即使在惊人的大激光强度下，共振和激光修饰态仍然发挥着相当大的作用，达到或超过10 TW/cm²。在高强度光-物质相互作用方面，这对应于Keldysh参数γ接近于单位。在这个更新建议中，我们将改进有关效率，鲁棒性和适用性的相干绝热控制方法。我们将研究基于盛装态和绝热通道的替代方法，以提高在高激光强度下的频率转换。此外，我们将研究相干-绝热量子动力学如何在更大的强度下向更强的光-物质相互作用方向变化，对应于小Keldysh参数γ<1。这将在微扰相互作用和强场状态之间转换的共振动力学中产生新的基本见解。提出的研究有助于回答基本的科学问题：通过共振应用相干绝热量子动力学的极限在哪里？我们能在多大程度上提高激光强度，同时还能通过修饰态和绝热通道利用共振和量子相干？当我们施加超过原子库仑势的强光场时，这些过程会发生怎样的变化？哪种控制方案最适合高强度的应用？有没有办法补偿激光引起的位移和共振的加宽？该项目将有助于澄清共振（无论是“裸”状态还是“激光修饰”状态）在高强度频率转换中的基本作用。

The aim of this renewal proposal is to extend our previous investigations in (sign removed) on harmonic generation, enhanced by coherent-adiabatic interactions via atomic multi-photon resonances. Our particular goal is to transfer concepts of coherent interactions, which are well established at moderate laser intensities, to high-intensity nonlinear optics. In our work we apply dressed states and adiabatic passage processes. The latter offer robustness with regard to fluctuations in experimental parameters and are applicable with short laser pulses of still sufficiently moderate bandwidth to selectively drive and exploit atomic resonances. Coherent-adiabatic control approaches via atomic resonances work well, if the driving laser field does not exceed the Coulomb field in the atom and, hence, destroy or strongly modify the level structure. On the other hand, efficient nonlinear optics usually require ultra-fast, high-intensity laser pulses. In this case, the level structure and spectral shape of transitions change considerably, e.g., by AC Stark shifts, which easily reach many THz per TW/cm² laser intensity. Application of resonance enhancements and adiabatic processes in this high intensity regime requires new approaches to deal with AC level shifts. As we recently demonstrated in (sign removed), resonances and laser-dressed states still play a considerable role even at surprisingly large laser intensities, up to or beyond 10 TW/cm². In terms of high intensity light-matter interaction, this corresponds to a Keldysh parameter γ approaching unity. In this renewal proposal we will refine the coherent-adiabatic control approaches with regard to efficiency, robustness, and applicability. We will investigate alternative approaches based on dressed states and adiabatic passage to enhance frequency conversion, driven at high laser intensity. Moreover, we will study how coherent-adiabatic quantum dynamics change for even larger intensities proceeding towards the regime of stronger light-matter interaction, corresponding to small Keldysh parameter γ<1. This will yield new fundamental insight in the dynamics of resonances in the transition between perturbative interaction and the strong field regime.The proposed investigations serve to answer the basic scientific questions: Where are the limits for applications of coherent-adiabatic quantum dynamics via resonances? How far can we increase the laser intensities and still exploit resonances and quantum coherences via dressed states and adiabatic passage? How do such processes change when we apply intense light fields, which start to exceed the atomic Coulomb potential? Which control scenarios are most appropriate for applications at higher intensities? Are there ways to compensate for laser-induced shifts and broadenings of resonances? The project will serve to clarify the fundamental role of resonances (no matter whether “bare” or “laser-dressed” states) in frequency conversion at high intensities.