Laser excitation of acoustic resonances in a spherical resonator

Laser excitation of nonradial and radial acoustic modes via transformation of absorbed optical into acoustical energy was studied in a spherical cavity. A computer-controlled technique was employed to record the resonance profiles with high precision as a function of CH4 pressure in the cavity. The conditions for efficient laser excitation of acoustic modes are discussed in terms of the overlap integral, which also explains the disappearance and reappearance of modes as a function of pressure. This effect was observed for the first radial mode in CH4. The investigation of the splitting of the degenerate first nonradial mode allowed an estimate of the deviations of the real cavity from the ideal spherical symmetry.