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Proceedings Paper

Femtosecond laser excitation and spectroscopy of liquid helium
Author(s): Alexander Vict Benderskii; Ruben Zadoyan; Nikolaus Schwentner; Vartkess Ara Apkarian
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Paper Abstract

Femtosecond laser pulses focused inside liquid helium initiate an excitation sequence that leads to formation of molecular Rydberg states He2 detected by fluorescence spectroscopy. Unlike in the case of longer laser pulses, the excitations may be created in a controllable way, at light intensities below dielectric breakdown. The initial step is ionization of He atoms, as demonstrate by charge separation in external electric field. A sequence of the subsequent processes is proposed, which accounts for rapid production of He2, in less than 10 ns, observed by nanosecond time- resolved laser induced fluorescence following the excitation pulse. the lowest triplet state excimers He2(3a), probed in the latter experiment, are long-lived and survive in concentrations of the order of 1011-1012 cm-3 on a millisecond time scale. Femtosecond time- resolved spectroscopy was performed on He2* molecules in liquid He, using the pump-probe sequence He2*(3a) + 790 nm yields He2*(3c), He2*(3c) + 790 nm yields He2*(3f). The observed decay of the transient signals with characteristic time 3.5 ps is thought to be due to solvent motion corresponding to the relaxation of the liquid helium 'bubble' around the intermediate He2*(3c) state.

Paper Details

Date Published: 24 April 1998
PDF: 12 pages
Proc. SPIE 3273, Laser Techniques for Condensed-Phase and Biological Systems, (24 April 1998); doi: 10.1117/12.306135
Show Author Affiliations
Alexander Vict Benderskii, Univ. of California/Irvine (United States)
Ruben Zadoyan, Univ. of California/Irvine (United States)
Nikolaus Schwentner, Univ. of California/Irvine (Germany)
Vartkess Ara Apkarian, Univ. of California/Irvine (United States)

Published in SPIE Proceedings Vol. 3273:
Laser Techniques for Condensed-Phase and Biological Systems
Norbert F. Scherer; Janice M. Hicks, Editor(s)

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