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Two-Photon Excitation of Low-Lying Electronic Quadrupole States in Atomic Clusters

V. O. Nesterenko·P. -G. Reinhard·T. Halfmann·L. I. Pavlov
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Abstract

A simple scheme of population and detection of low-lying electronic quadrupole modes in free small deformed metal clusters is proposed. The scheme is analyzed in terms of the TDLDA (time-dependent local density approximation) calculations. As test case, the deformed cluster $Na^+_{11}$ is considered. Long-living quadrupole oscillations are generated via resonant two-photon (two-dipole) excitation and then detected through the appearance of satellites in the photoelectron spectra generated by a probe pulse. Femtosecond pump and probe pulses with intensities $I = 2\cdot 10^{10} - 2\cdot 10^{11} W/cm^2$ and pulse duration $T = 200 - 500$ fs are found to be optimal. The modes of interest are dominated by a single electron-hole pair and so their energies, being combined with the photoelectron data for hole states, allow to gather new information about mean-field spectra of valence electrons in the HOMO-LUMO region. Besides, the scheme allows to estimate the lifetime of electron-hole pairs and hence the relaxation time of electronic energy into ionic heat.

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V. O. Nesterenko, P. -G. Reinhard, T. Halfmann, L. I. Pavlov. 2005-11-08. Two-Photon Excitation of Low-Lying Electronic Quadrupole States in Atomic Clusters. https://doi.org/10.1103/physreva.73.021201

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