Münster 1999 – scientific programme
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HL: Halbleiterphysik
HL 29: Ultrakurzzeitdynamik I
HL 29.11: Talk
Thursday, March 25, 1999, 13:00–13:15, H2
Few-cycle THz spectroscopy of semiconductor quantum structures — •Rudolf Bratschitsch1, Roland Kersting1, Edwin Thaller1, James Heyman2, Gottfried Strasser1, and Karl Unterrainer1 — 1Institut für Festkörperelektronik, TU-Wien, Floragasse 7, A-1040 Wien — 2Macalester College, St. Paul, MN 55105, USA
In our experiments we generate few-cycle THz pulses by ultrafast laser excitation of coherent plasma oscillations in n-doped GaAs. This THz radiation can drive electronic intersubband transitions in modulation doped quantum well structures. By using a cross-correlation technique we are able to detect both amplitude and phase of the transmitted radiation. We show results for both resonant and non-resonant excitation of the quantum well intersubband transition which serves as a model two level system. While resonant excitation shows the signature of the free induction decay a completely different observation is made in the off-resonant case: at early times the coherent polarization oscillates with the frequency of the exciting THz-pulse but after the end of the driving pulse the electrons inside the quantum well perform a phase jump and begin to oscillate with the eigenfrequency of the intersubband transition. Experiments are under way to selectively populate the upper state of the two level system by interband pumping and to probe the population by a delayed THz pulse.