arXiv subjects

E. Matthias

Publications and source records attributed to E. Matthias.

3 recordsLinked to original sources

arXiv1997

Does femtosecond time-resolved second-harmonic generation probe electron temperatures at surfaces?

Femtosecond pump-probe second-harmonic generation (SHG) and transient linear reflectivity measurements were carried out on polycrystalline Cu, Ag and Au in air to analyze whether the electron temperature affects Fresnel factors or nonlinear susceptibilities, or both. Sensitivity to electron temperatures was attained by using photon energies near the interband transition threshold. We find that the nonlinear susceptibility carries the electron temperature dependence in case of Ag and Au, while for Cu the dependence is in the Fresnel factors. This contrasting behavior emphasizes that SHG is not a priori sensitive to electron dynamics at surfaces or interfaces, notwithstanding its cause.

cond-mat↗

arXiv1997

Nonequilibrium Magnetization Dynamics of Nickel

Ultrafast magnetization dynamics of nickel has been studied for different degrees of electronic excitation, using pump-probe second-harmonic generation with 150 fs/800 nm laser pulses of various fluences. Information about the electronic and magnetic response to laser irradiation is obtained from sums and differences of the SHG intensity for opposite magnetization directions. The classical M(T)-curve can be reproduced for delay times larger than the electron thermalization time of about 280 fs, even when electrons and lattice have not reached thermal equilibrium. Further we show that the transient magnetization reaches its minimum approx. 50 fs before electron thermalization is completed.

cond-mat↗

arXiv1997

Second-order magnetic contributions to the hyperfine splitting of the 5snd ^1D_2 states in ^87Sr

The hyperfine structure of 5snd ^1D_2 states in ^{87}Sr was studied for principal quantum numbers 11 <= n <= 25 by Doppler-free two-photon excitation combined with thermionic detection. Based on the more accurate data, compared to previous results, the hyperfine structure was analysed by second order perturbation theory using MQDT wavefunctions. As a result we find that the surprisingly large B-factors obtained by fitting the data with the Casimir formula do not reflect a quadrupolar interaction but rather consist predominantly of second order magnetic dipole contributions. Further, inconsistencies in the King plot of odd-even isotope shifts were removed by this type of analysis. The result demonstrates the importance of higher order effects in hyperfine splittings of excited states in atoms with two valence electrons, even when the fine structure splitting is large compared to the hyperfine splitting.

physics.atom-ph↗