Berlin 2008 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 39: Ultra fast phenomena
HL 39.7: Talk
Thursday, February 28, 2008, 12:45–13:00, ER 270
Ultrafast dynamics of coherent optical phonons in α-quartz — •Konrad von Volkmann1, Tobias Kampfrath1, Marcel Krenz1, Alexander Grujic2, Christian Frischkorn1, and Martin Wolf1 — 1Freie Universität Berlin, Berlin, Germany — 2Femtolasers GmbH, Fernkorngasse 10, 1100 Vienna, Austria
Femtosecond laser excitation of α-quartz causes oscillation of the transmitted intensity and polarization of probe light. This is due to coherent phonons modulating the real and imaginary part of the refractive index α-quartz ñquartz= n +i k. Optical phonon modes are found at 3.9, 6.3, 10.5, 12.2, and 13.9 THz. The observed amplitudes significantly depend on the probe method, either transient absorption (yielding k) or ellipsometry (leading to n).
We present temperature and pump-polarization dependent data for both probe methods. The polarization dependence will be discussed in terms of impulsive stimulated Raman scattering as excitation mechanism and a detailed analysis of the corresponding Raman tensors will be given. Previous measurements have shown a pump-fluence independent lifetime which indicates that the decay mechanism of the lattice vibrations is phonon-phonon scattering. The temperature dependence of the phonons confirms this finding and enables a discussion of the scattering rates and the involved phonons.