HYDRODYNAMIC SIMULATIONS OF BUBBLE COLLAPSE AND PICOSECOND SONOLUMINESCENCE

Numerical hydrodynamic simulations of the growth and collapse of a 10 mu m air bubble in water were performed. Both the air and the water ar e treated as compressible fluids. The calculations show that the colla pse is nearly isentropic until the final 10 ns, after which a strong s pherically converging shock wave evolves and creates enormous temperat ures and pressures in the inner 0.02 mu m of the bubble. The reflectio n of the shock from the center of the bubble produces a diverging shoc k wave that quenches the high temperatures (>30 eV) and pressures in l ess than 10 ps (full width at half maximum). The picosecond pulse widt hs are due primarily to spherical convergence/divergence and nonlinear stiffening of the air equation of state that occurs at high pressures . The results are consistent with recent measurements of sonoluminesce nce that had optical pulse widths less than 50 ps and 30 mW peak radia ted power in the visible.