Plasma diagnostics and sonoluminescence

Abstract

Plasma diagnostic techniques are applied to single- and multibubble sonoluminescence (SBSL and MBSL). In the case of SBSL the electronic temperature (Te) and density (Ne) are deduced on basis of the spectrum of an Ar bubble in water [the recording by R. Hiller et al., Science 226, 248 (1994)]. This analysis, based on the emission continuum, reveals that the intracavity sonoluminescent medium behaves as a sparklike plasma highly charged with energy (Te=20 000 K; Ne=1025 m−3). In the case of MBSL (Ar bubbles in water), the method of the ratio ‘‘intensity of a line/intensity of the adjacent continuum’’ is used in order to determine Te. The higher the ultrasonic frequency, the hotter the bubble interior is. Two scenarios are analyzed (plasmas with a degree of ionization 〈or〉 1%) and the order of magnitude of Ne is estimated. The conditions associated with multibubble systems appear to be of the same kind as those associated with SBSL, with a lesser degree of intensity, however. The possibility is discussed that local thermodynamic equilibrium (LTE) or partial LTE is reached. [Work supported by F.N.R.S., Belgium.]