Dressed states and adiabatic passage for high-intensity nonlinear optics

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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.