Explosive evaporation of Rb or K fractal clusters by low power CW radiation in the presence of excited atoms1
Institute Automation and Electrometry, Russian Academy of
Science, Prosp. Koptyug,
2 Dipartimento di Fisica dell’Università di Ferrara and Istituto Nazionale di Fisica Nucleare Sezione di Ferrara, Via G. Saragat 1, 44122 Ferrara, Italy
a e-mail: email@example.com
Received in final form: 22 March 2012
Published online: 23 May 2012
In this paper we describe a new, spectacular, unpredictable effect of the explosive evaporation of metallic Rb or K fractal clusters, only in the presence of excited atoms stimulated by resonant CW laser radiation in a heat-pipe glass cell. Evaporation occurs at low laser-power density, in the presence of a buffer gas. The effect consists of the generation of optically thick, sharply localized alkaline metals vapour clouds propagating in the cell against the laser beam. These clouds are charged and exhibit a strong luminescence of Rb or K spectral lines. We believe that the explosive evaporation of metallic fractal clusters observed is explained by the laser excitation of alkali atoms. The excited atom collides into the surface of the clusters and transfers its internal energy to the surface locally. This energy greatly raises the temperature of this local part of the clusters surface, melts it and decreases the fractal surface area. Because, in general, any fractal cluster systems have a high surface energy, some of processes which leads to decreasing their surface area can liberate the surface energy. This energy increases the total temperature of the clusters and eventually leads to the thermal explosion of the cluster.
Key words: Clusters and Nanostructures
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© EDP Sciences, Società Italiana di Fisica and Springer-Verlag 2012