Düsseldorf 2007 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 4: Atomic Clusters II
A 4.5: Vortrag
Montag, 19. März 2007, 15:15–15:30, 6G
Harmonic generation in the laser-cluster interaction
— •Mrityunjay Kundu and Dieter Bauer — Max-Planck-Institut für Kernphysik, Postfach 103980, 69029 Heidelberg, Germany
Laser-atom or laser-molecule interaction typically shows higher order harmonics of the incident laser frequency. Experiments with atomic clusters, on the other hand, demonstrate the generation of low-order harmonics of higher intensity than with rare-gas atoms. By particle-in-cell (PIC) simulations of ArN clusters (with N up to 92096 atoms) in 800 nm, short (<30 fs) laser pulses, we investigate why the emission is restricted to lower order harmonics. We show that the dipole radiation of the bound electrons and the free electrons counteract each other, and the resulting destructive interference limits the harmonics in to low orders. In this short-pulse regime the free electron population increases by absorbing laser energy only via the nonlinear resonance NLR [1,2]. We find that occurrence of the NLR coincides with predominant dipole radiation. However, the total dipole radiation shows enhanced third and fifth harmonic emission at times when the Mie-frequency of the ionizing and expanding cluster linearly resonates with the respective harmonics. The harmonic emission may be used to study the cluster dynamics with pump-probe experiments. By PIC simulations, we discuss a possible pump-probe experiment to predict the maximum of the cluster charge density at a given laser intensity.
[1] M. Kundu and D. Bauer, Phys. Rev. Lett., 96, 123401 (2006).
[2] M. Kundu and D. Bauer, Phys. Rev. A., 74, 063202 (2006).