Opto-Acoustic Response From Absorbed Particle in Liquid
V.In'kov, I.M.Pelivanov (Faculty of Physics, Moscow State University, Moscow, Russia); A.A.Karabutov (International Laser Center, Moscow State University, Moscow, Russia)
This work is devoted to a theoretical analysis of the opto-acoustic effect in an inhomogeneous medium consisting of an absorbing spherical particle in an immersion (nonabsorbing) liquid irradiated with laser pulses. The problem of determining the opto-acoustic response in an inhomogeneous medium is separated into three sequential steps: determination of the distribution of the light flux in a medium, calculation of consequent temperature field distribution, and the solution of the acoustic problem of thermo-optical excitation of sound by thermal sources [Karabutov A.A., Podymova N.B., Letokhov V.S. // Appl. Phys., 1996, vol.63, p.545-563]. The independence as well as linear one of a thermal expansion coefficient from a temperature was taken into account. The cases of thermally large and thermally small particles are analyzed. In the case of a thermally large particle, the time profile of the pressure of the acoustic signal strongly depends on the relation between the coefficient of light absorption by a particle and its radius, as well as on the duration of the laser pulse. In the case of a thermally small particle, a heating of a particle takes place uniformly at its volume and the opto-acoustic pulse is excited only by thermal expansion of immersed layer of liquid.
Section : 9