Chemical generation of sound waves: shock waves and a “giant” photoacoustic effect

When a suspension of carbon particles in water is irradiated by a high power, pulsed laser an anomalously large photoacoustic effect is generated which has an amplitude on the order of 2000 times larger than that produced by a dye solution with an equivalent absorption coefficient. Transient gratings generated in carbon suspensions with high power lasers show a doubling of the acoustic frequency corresponding to the optical fringe spacing of the grating. Both effects are attributed to high temperature chemical reactions initiated by the laser that consume energy and produce gaseous reaction products. A theory for generation of the photoacoustic effect is given that is applied to the reactions taking place in the carbon suspension