Allan D. Pierce
Guido V. H. Sandri
Dept. of Aerosp. and Mech. Eng., Boston Univ., 110 Cummington St., Boston, MA 02215
An order of magnitude estimate is provided of the duration of the extremely short flashes of light that are emitted at regular intervals when a spherical gas bubble is made to oscillate by ultrasonic excitation---the phenomenon known as sonoluminescence. The estimate is based upon a recently proposed mechanism for this phenomenon [H. P. Greenspan and A. Nadim, Phys. Fluids A 5, 1065--1067 (1993)], which envisions the formation of spherically converging shock waves within the oscillating gas bubble, which itself acts as a spherical ``piston.'' As the shock wave converges toward the geometric center of the bubble, it gives rise to extremely high temperatures, ionizing the gas and leading to the emission of light. In the present contribution, it is shown that under reasonable assumptions on the distance and strength of the shock from the bubble center when it first occurs, the time during which the gas near the bubble center is hot enough to produce visible light is on the order of tens of picoseconds, in agreement with experimental observations.