Intraexcitonic coherent nonlinear optics in quantum wells

A fundamental problem in light-matter interaction is the coupling of an intense, monochromatic electromagnetic wave with a quantum mechanical two-level system. One effect related to this is the Autler-Townes or AC Stark effect. Originally observed and described in molecular spectroscopy the effect refers to a splitting of an energy level that is resonantly coupled via intense radiation to an adjacent level, i.e. the states get ”dressed” by the light-matter interaction. We investigate this effect using a free-electron laser (FEL) driven intra-excitonic transition between the heavy-hole 1s and 2p states in a semiconductor multiple quantum well. We have observed distinct intensity- and wavelength dependent Rabi sidebands of the 1s exciton line when the FEL was tuned around the 1s-2p transition [1]. We also present measurements at higher electric fields exploring the regime beyond the rotating-wave approximation (RWA), where the Rabi energy is comparable to the transition energy. Theoretical calculations support the understanding of the underlying processes, which is especially interesting for the regime beyond the RWA. Also temperature-dependent measurements have been done and a clear Rabi-sideband behavior is observable up to 200 K where the thermal energy already exceeds the exciton binding energy by a factor of 1.7 [2]. A threefold NIR transmission change at 200 K on picosecond timescales could be promising for optical modulators with Peltier-cooling.
[1] M. Wagner, H. Schneider, D. Stehr, S. Winnerl, A. M. Andrews, S. Schartner, G. Strasser, and M. Helm, Phys. Rev. Lett. 105, 167401 (2010)
[2] M. Wagner, M. Teich, M. Helm, and D. Stehr, Appl. Phys. Lett. 100, 051109 (2012)