Self-holograms of laser-induced surface depressions in heavy hydrocarbons

Among applications of lasers in the petroleum industry are samples of heavy oils heated by a He-Ne laser beam. It is shown that laser power concentrations as low as 1 mW/mm(2) induce noticeable changes in the form of the surface. The far-field diffraction pattern of the reflected wave can be considered as a self-hologram of the hole, with the paraxial focus of the bottom of the hole as a point reference source. Annular images corresponding to different zones of the hole are reconstructed by illuminating the hologram with a spherical wave. A geometrical model of the shape of the irradiated surface is proposed and compared with experimental data.