THERMOELEASTIC RESPONSE OF POLYCRYSTALLINE Si TO AN INTENSE CW LASER BEAM.

We have used analytic methods to obtain closed forms for the thermal strains induced on polycrystalline Si when a cw visible laser beam is focused on its surface. The material is treated as isotropic with appropriately chosen elastic constants. The solution is expressed in terms of the Galerkin vectors for a semi-infinite bulk medium under point dilatation. The results show that considerable strains (corresponding to typical compressive stresses up to 0. 5 GPa) are produced even for laser power densities lower than the threshold for melting. Three-dimensional graphical representations are given for the elastic displacements, the strain, and stress components, as a function of appropriate geometrical coordinates.