A N T - P H - 9 50 60 24 Theory of quantum radiation observed as sonoluminescence

Sonoluminescence is explained in terms of quantum radiation by moving interfaces between media of di erent polarizability. In a stationary dielectric the zero-point uctuations of the electromagnetic eld excite virtual two-photon states which become real under perturbation due to motion of the dielectric. The sonoluminescent bubble is modelled as an optically empty cavity in a homogeneous dielectric. The problem of the photon emission by a cavity of time-dependent radius is handled in a Hamiltonian formalism which is dealt with perturbatively up to rst order in the velocity of the bubble surface over the speed of light. A parameter-dependence of the zero-order Hamiltonian in addition to the rst-order perturbation calls for a new perturbative method combining standard perturbation theory with an adiabatic approximation. In this way the transition amplitude from the vacuum into a two-photon state is obtained, and expressions for the single-photon spectrum and the total energy radiated during one ash are given both in full and in the short-wavelengths approximation when the bubble is larger than the wavelengths of the emitted light. A model pro le is assumed for the time-dependence of the bubble during the collapse, and in this model the radiated energy and the spectrum are calculated numerically and in the shortwavelengths limit also analytically. It is shown analytically that the spectral density has the same frequency-dependence as black-body radiation; this is purely an e ect of correlated quantum uctuations at zero temperature. The present theory clari es a number of hitherto unsolved problems and suggests explanations for several more. Possible experiments that discriminate this from other theories of sonoluminescence are proposed. PACS numbers: 03.70.+k, 11.10.-z, 42.50.Lc, 78.60.Mq e-mail to: [email protected]