Efficient generation of surface acoustic waves by thermoelasticity

Short laser pulses were used for generating surface acoustic waves (SAW's) on optically opaque solids via the thermoelastic effect. The spatial and temporal shapes of the laser pulses were either a spot or a line of variable total width delta = 2 alpha with a Gaussian power distribution. Maximal effciency is obtained when alpha = ypsilon sub R tau (ypsilon sub : Rayleigh velocity, 2 tau : total laser-pulse length). This condition is caused by interference effects between the individual frequency components radiating from the area of the thermoelastic source. If the intensity of the laser beam were 100% modulated at a given frequency, maximal efficiency would occur if k sub R = square root 2/alpha(k sub R: wave vector of the SAW's).