Laser generation of acoustic waves in the ablative regime

A practical model of acoustic wave generation by a pulsed laser source in t he ablative regime is presented. The pressure exerted on the surface during Q-switched laser heating is calculated through a finite difference solutio n of the vaporization problem. The epicentral displacement is found through summation of the displacement field induced by the vaporization process wi th that caused by thermoelastic expansion. The model is restricted to the w eakly ablative regime in the absence of a backing gas. The results are comp ared to the epicentral displacements generated in aluminum samples under ro ugh vacuum conditions at generating wavelengths of 532 and 1064 nm. The wav eforms compare well over a limited irradiance range. The effects of rough v acuum conditions on the generated acoustic signals are also examined and co mpared to signals generated in the presence of a backing gas. The divergenc e in the shape and amplitude of these signals observed under highly ablativ e conditions is discussed. (C) 1999 American Institute of Physics. [S0021-8 979(99)06104-6].