Comment on ``Sonoluminescence as Quantum Vacuum Radiation''

Sonoluminescence occurs when tiny bubbles rilled with noble gas atoms are driven by a sound wave. Each cycle of the driving field is accompanied by a collapse phase in which the bubble radius decreases rapidly until a short but very strong light flash is emitted. The spectrum of the light corresponds to very high temperatures and hints at the presence of a hot plasma core. While everyone accepts that the effect is real, the main energy focussing mechanism is highly controvers...

Sonoluminescence is the intriguing phenomenon of strong light flashes from tiny bubbles in a liquid. The bubbles are driven by an ultrasonic wave and need to be filled with noble gas atoms. Approximating the emitted light by blackbody radiation indicates very high temperatures. Although sonoluminescence has been studied extensively, the origin of the sudden energy concentration within the bubble collapse phase is still controversial. It is hence difficult to further increase ...

We consider the correlation of the electromagnetic field to determine spatial coherence inside a sonoluminescing bubble. We explicitly calculate the first order correlation function for two limiting cases of the excitation field: a blackbody spectrum and a discrete multifrequency spectrum. The correlation length for blackbody fields at temperatures between 3000 K and 10000 K is found to be on the order of the optical wavelength, increasing with decreasing temperatures. We pre...

It has been suggested by various authors that the `dynamical Casimir effect' might prove responsible for the production of visible-light photons in the bubble collapse which occurs in sonoluminescence. Previously, I have argued against this point of view based on energetic considerations, in the adiabatic approximation. Those arguments have recently been strengthened by the demonstration of the equivalence between van der Waals and Casimir energies. In this note I concentrate...

In a companion paper [quant-ph/9904013] we have investigated several variations of Schwinger's proposed mechanism for sonoluminescence. We demonstrated that any realistic version of Schwinger's mechanism must depend on extremely rapid (femtosecond) changes in refractive index, and discussed ways in which this might be physically plausible. To keep that discussion tractable, the technical computations in that paper were limited to the case of a homogeneous dielectric medium. I...

We investigate several means of coupling between a sonoluminescing bubble and an applied magnetic field. Recent experiments show a strong quadratic dependence between the forcing pressures required for stable sonoluminescence and magnetic field amplitude. However, all coupling mechanisms calculated here for comparable magnetic fields involve energies no more than one percent the mechanical energy of bubble collapse. We conclude that the applied field must influence the system...

Sonoluminescence is a phenomenon involving the transduction of sound into light. The detailed mechanism as well as the energy-focusing potentials are not yet fully explored and understood. So far only optical photons are observed, while emissions in the ultra-violet range are only inferred. By doping the fluorescent dye quinine into water with dilute sulphuric acid, the high energy photons can be converted into the optical photons with slower decay constants. These sonolumine...

Light emission in sonoluminescence is shown to be a lasing process with a wide gain bandwidth. Population inversion of the gas molecules inside the bubble is achieved by hydrodynamical pumping. Analytic expressions are derived for the sonoluminescence pulse shape, pulse width, and their codependence on the spectrum and intensity in physically relevant regimes. A detailed comparison with experiments(R. Hiller et al., Phys. Rev. Lett. 80, 1090 (1998); M.J. Moran et al., Phys. R...

In single-bubble sonoluminescence, a bubble trapped by a sound wave in a flask of liquid is forced to expand and contract; exactly once per cycle, the bubble emits a very sharp ($< 50 ps$) pulse of visible light. This is a robust phenomenon observable to the naked eye, yet the mechanism whereby the light is produced is not well understood. One model that has been proposed is that the light is "vacuum radiation" generated by the coupling of the electromagnetic fields to the su...

The phenomenon of sonoluminescence (SL), originally observed some sixty years ago, has recently become the focus of renewed interest, particularly with the discovery that one can trap a single bubble and induce it to exhibit SL stably over a large number of acoustical cycles. In this work we shall adopt a version of the provocative suggestion put forward by Schwinger: the mechanism responsible for the radiation in SL is a dynamic version of the Casimir effect. It has been k...