A short pulse of laser light can act as a source of acoustic energy for acoustic imaging. Although tllf're are a number of mechanisms by which the light pulse may generate sound, all require a pulse of high peak power density and short duration. In this work, we address exampl('s wl1(>re the material is highly absorbing at the laser -wavelength, and the sound is gem'rated near t.he surface. In these cases, there exist two different mechanisms which can COllwrt the light to sound. The first is heating followed by expansion, and the second is gelH'ratioll of a plasma in the air above the surface. In the first case, sound generation occms in tIl(' medium of interest and the energy efficiency can be very high, in the sense that no refi('ction losses occur. We present two applications from our own research.
