Regensburg 2007 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 29: Symposium THZ interactions
HL 29.4: Hauptvortrag
Mittwoch, 28. März 2007, 15:45–16:15, H15
Nonlinear terahertz and midinfrared response of n-type GaAs — •Michael Woerner1, Peter Gaal1, Wilhelm Kühn1, Klaus Reimann1, Thomas Elsaesser1, Rudolph Hey2, and Klaus Ploog2 — 1Max-Born-Institut , Berlin — 2Paul-Drude-Institut, Berlin
In most THz experiments the THz radiation is used as a linear probe. Using THz radiation for nonlinear excitation requires the ability to generate high enough THz intensities. Our recent development of a simple and reliable method to generate THz pulses with high electric field amplitudes [1] has paved the way for nonlinear optics in the THz regime. We present two experiments on n-type GaAs which are in strong contrast to the predictions of Drude theory: (i) Nonlinear propagation of intense THz pulses through a thin n-type GaAs layer shows a coherent emission at 2 THz with a picosecond decay of the emitted field, despite the ultrafast carrier-carrier scattering at a sample temperature of 300 K [2]. While the linear THz response is in agreement with the Drude response of free electrons, the nonlinear response is dominated by the super-radiant decay of optically inverted impurity transitions. (ii) A nonlinear THz pump--midinfrared probe experiment shows a quantum kinetic phenomenon of the electron--LO phonon dynamics. Ultrafast acceleration of free carriers in n-type GaAs in a strong THz field results in an oscillatory occurrence of midinfrared gain/absorption with the LO phonon frequency. [1] T. Bartel et al., Opt. Lett. 30, 2805 (2005). [2] P. Gaal et al., Phys. Rev. Lett. 96, 187402 (2006).