The relationship between the method of acoustic excitation and the stability of single bubble sonoluminescence for various noble gases

When a gas bubble is properly excited it will oscillate and may undergo implosions during which the gas in the bubble can become so compressed that a plasma is formed, resulting in the emission of photons. That is, light pulses may occur during implosions. This phenomenon has been known of for more than 60 years and is called sonoluminescence. It is of great interest to scientists and engineers for high temperature chemical reactions, remediation of contaminated liquids and, more recently, the possibility of thermonuclear fusion. Measurements using mixed frequency ultrasonic bubble excitation were performed for different dissolved noble gases at various temperatures. The transient radius of the bubble was measured using Mie scattering and sonoluminescence (i.e., photon) emission was detected using two photomultipliers, which were band pass filtered to be sensitive to different parts of the emission spectrum. The reduction in the ambient radius was identified as being directly related to bubble stability (i.e., the smaller the ambient radius, the less likely is the bubble to break up). In addition, the apparent lower frequency between strong implosions (i.e., the longer time for interfacial perturbations to damp) is also important. Interestingly, it was found that while the intensity of the light emissions was directly related to the amplitude of the imposed excitation pressure, the corresponding average gas temperature was unaffected.