Berlin 2005 – scientific programme

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MO: Molekülphysik

MO 22: Poster I

MO 22.13: Poster

Saturday, March 5, 2005, 10:30–12:30, Poster HU

Femtosecond photoelectron spectroscopy of sodium clusters — •Abdollah Malakzadeh, Christian Hock, Christof Bartels, Raphael Kuhnen, and Bernd v.Issendorff — Fakultät für Physik, Universität Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg

Recently we have shown that the electron gas in a free sodium cluster can be heated by a single fs-laser pulse to temperatures high enough for thermal electron emission to occur. This emission can be described by a simple model: the laser excites the collective motion of the electrons (the plasmon), which after a very short time (a few fs) decays into single electron-hole excitations. Due to the strong electron-electron interaction within a short time this nonthermal energy distribution of the electrons is transformed into a thermal one. The electron gas then cools by electron-phonon coupling. Time-resolved pump-probe photoelectron and photofragmentation spectroscopy has been applied to measure the electron-phonon-coupling constant as a function of cluster size. This has been done using relatively long laser pulses (τ ≈ 200 fs). In order to obtain more information about the early stages of the excitation, shorter laser pulses are necessary. Therefore a NOPA (noncollinear optical parametric amplifier) has been constructed, which allows the production of wavelength tunable, short (τ < 50 fs) laser pulses, as well as a hollow capillary compressor. The performance of these devices and first results for sodium clusters are discussed.