M. Visser et al., Sonoluminescence: Bogolubov coefficients for the QED vacuum of a time-dependent dielectric bubble, PHYS REV L, 83(4), 1999, pp. 678-681
We extend Schwinger's ideas regarding sonoluminescence by explicitly calcul
ating the Bogolubov coefficients relating the QED vacuum states associated
with changes in a dielectric bubble. Sudden (nonadiabatic) changes in the r
efractive index lead to an efficient production of real photons with a broa
dband spectrum, and a high-frequency cutoff that arises from the asymptotic
behavior of the dielectric constant.