A theory of the excitation of ultrasound waves arising from photoelastic coupling with light is presented in this article. Using several reasonable approximations, a numerical calculation of the transient stimulated Brillouin scattering process shows that a large amplitude of acoustic wave can be built up during the pulse of pump light, and it may result in damage to optical materials. This model gives a damage threshold value of ∼30–50 J/cm2when using Gaussian or square nanosecond pulses on optical materials. ©1997 American Institute of Physics.