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HL: Fachverband Halbleiterphysik

HL 50: Ultra fast phenomena

HL 50.8: Vortrag

Freitag, 27. März 2009, 12:15–12:30, BEY 118

Nonlinear THz spectroscopy of excitons in optically excited semiconductors — •Johannes T. Steiner, Mackillo Kira, and Stephan W. Koch — Fachbereich Physik, Philipps-Universität, Renthof 5, D-35032 Marburg

We theoretically investigate the interaction of optically-excited semiconductors with strong coherent terahertz (THz) pulses using a fully microscopic many-body theory. In contrast to optical fields, THz fields are resonant with intraband transitions and can directly induce internal transitions of the optically-excited quasi-particles [1]. In the past, time-resolved linear THz spectroscopy has been used, e.g., to monitor the build-up of exciton populations. In my talk, I will concentrate on situations where a strong THz pulse induces nonlinear transitions between different exciton states, e.g., between the 1s and 2p exciton states. The THz pulse can interact either with coherent excitons, i.e., interband polarization which decays within a few picoseconds after optical excitation or with incoherent excitons, i.e., genuinely bound electron-hole pairs. I will discuss the signatures of THz-induced nonlinearities which include Rabi oscillations, ponderomotive effects and extreme-nonlinear dynamics. The nonlinear THz regime is distinguished by the fact that three characteristic energies – the 1s-to-2p transition energy, the Rabi energy and the ponderomotive energy – are of the same order of magnitude. The theory is quantitatively compared to recent experiments in different material systems.

[1] M. Kira and S. W. Koch, Prog. Quantum Electron. 30, 155 (2006)