%0 Generic
%A Kundu, Mrityunjay
%D 2007
%F heidok:7941
%K Nanoplasma , Coulomb-Explosion , Harmonische EmissionNanoplasma , Coulomb explosion , Harmonic emission, laser-irradiated atomic cluster
%R 10.11588/heidok.00007941
%T Energy absorption, ionization, and harmonic emissionin laser-irradiated atomic clusters
%U https://archiv.ub.uni-heidelberg.de/volltextserver/7941/
%X The excellent coupling of laser light to atomic clusters is a known, experimentally established fact. However, the physical mechanism of laser absorption is still controversially discussed. Linear resonance (LR) absorption occurs for sufficiently long laser pulses of optical or longer wavelengths. Here the Mie-plasma frequency initially rises above the laser frequency, then drops due to cluster expansion and therefore meets the laser frequency at some point. Instead, in few-cycle laser pulses this LR is not met but efficient laser energy absorption is found to persist. By particle-in-cell simulations and analytical modelling it is shown that the cluster electrons contributing to efficient absorption pass a nonlinear resonance (NLR), i.e., the instantaneous frequency of their motion in a time-dependent, anharmonic potential transiently meets the laser frequency. For a given laser intensity and cluster it is further shown that an optimum laser wavelength for absorption exists which typically lies in the ultraviolet regime. This yields a higher laser absorption efficiency than employing LR during the cluster expansion. The emission spectrum of laser-irradiated clusters is also investigated. Only the deeply bound, coherently oscillating electrons in the cluster potential contribute to low-order harmonic emission. In contrast, electrons crossing the NLR and leaving the cluster emit radiation with random phase which inhibits high-order harmonics. A pump-probe experiment is proposed to measure the time-dependent nano-cluster charge density by detecting the harmonic radiation.