ray showers. Intense laser beams and radiation acoustics Later G. Askaryan showed that intense laser beam passing through matter also generates sound waves. This effect may be used for processing and for destruction of matter. As a result of this series of investigations, a new branch of physics was created, radiation acoustics, and G. Askaryan was the founder. Interaction of laser beam with substances After discovery of lasers, G. Askaryan began to investigate interaction of laser beam with various substances. At that time physicists who worked with lasers, used to break through thin metal specimens (usually, razor blades) with laser beam. It was something like a game. G. Askaryan also rendered tribute to this game. He noticed that holes made by laser beam were of two kinds. When he used laser of moderate power, the edges of aperture were smooth, as if the aperture was melted through (indeed, it was melted). However, the hole made by powerful laser had rough uneven edges, as if the hole was broken through, not melted. At first G. Askaryan supposed that it was the light pressure which knocked out the part of razor blade in the light spot, however, simple estimates showed that the assumption was wrong. The problem was later cleared up by G. A. Askaryan and E. M. Moroz. The explanation was the following. The beam from a powerful laser heats metallic surface so intensely that surface layer turns into a vapor before the heat penetrates into next layers. The vapor is ejected from the surface. Thereby, a force arises which acts on the part of surface within the spot. This force is numerically equal to the momentum of vapor ejected during a unit of time. Such is the reaction of vapor on the surface. And in the case of powerful laser this reaction is so strong that the metal within the spot is torn out. The reaction of the vapor gives pressure that is many orders greater than the light pressure. Vaporizing ablation is now used for compressing the nuclear fuel in the problem of laser induced controlled thermonuclear reactions. Self-focusing of waves Perhaps one of the most brilliant of Askaryan's discoveries was the self-focusing of light. In the medium with third order nonlinear polarization, the refractive index can be represented as n = n0 + n2I, where n0 is the linear refractive index, n2 is an optical constant characterizing the