Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 53: Ultra fast phenomena

HL 53.8: Talk

Friday, March 30, 2007, 12:45–13:00, H15

Ultrafast dynamics of coherent opticalphonons in α-quartz — •Konrad von Volkmann, Tobias Kampfrath, Lucca Perfetti, Jan Nötzold, Christian Frischkorn, and Martin Wolf — Freie Universität Berlin, Berlin, Germany

Femtosecond laser excitation of coherent phonons gives rise to an oscillatory modulation of the real and imaginary part of the refractive index of α-quartz ñ_quartz= 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).

For both probe mechanisms, we present polarization, pump-wavelength and temperature dependent data and discuss the observed dynamics in terms of impulsive stimulated Raman scattering as excitation mechanism. We find that the phonon peaks shift with temperature towards lower energies accompanied by a drop of the lifetime of the phonons. Together with a pump-fluence independent lifetime, this indicates that the decay mechanism of the phonons is phonon-phonon scattering, rather than electron-hole pair excitation.