Characteristics of photostrictively produced optoacoustic pulses

The characteristics of optoacoustic pulses produced by photostrictive means are investigated. Since such acoustic disturbances have a nonthermal origin, and can be as short as the inverse of the highest frequency phonons that couple the photostrictive deformation to the lattice, ultrashort (subpicosecond) optoacoustic pulses can be produced. the differences are discussed between cold photostrictive optoacoustic pulses and those produced by thermal means in terms of what may be called a rise time reduction factor that characterizes the relative pulsewidths of the thermal to nonthermal pulses; a criterion for picking materials that would show large rise time reduction factors is given. the strength of a photostrictive optoacoustic pulse, in the high-intensity regime, is calculated. Since the nonthermal nature of the photostrictive optoacoustic pulse is important in the production of ultrashort optoacoustic pulses, thermalization mechanisms subsequent to laser irradiation of the photostrictive material are examined. It is shown that there is a trade-off between the strength of the compression and the initial temperature that it exhibits, and an estimate of the expected initial temperature of the compression is given. The characteristics of photostrictively generated optoacoustic pulses and those produced by other means, including nonthermal electrostrictive generation, are compared.