Nature of the “Extreme Conditions” in Single Sonoluminescing Bubbles

A plasma diagnostics analysis is reported which looks at the experimental spectrum of the sonoluminescence emitted by a single argon bubble oscillating nonlinearly in an acoustic field. Under the hypothesis that the bubble is mainly filled with Ar atoms able to participate in the plasma, an order-of-magnitude estimation of the electron density ( N e ) associated with the intracavity medium gives N e ≈ 10 25 m -3, with an electronic temperature estimated to be about 20 000 K, perhaps more. This analysis suggests that the conditions at the root of single-bubble sonoluminescence are highly energy charged and may be compatible with a sparklike process. The plasma developed inside the argon bubble is assumed to be in local thermodynamic equilibrium.