Investigation of the focusing action of media with residual stresses

An experimental study was made of glass plates which exhibited a focusing action after illumination with a CO laser beam. Focusing of helium–neon laser radiation by these plates gave rise to a spatial structure similar to that observed in the thermal self-focusing of light. When the region illuminated with the CO₂ laser was greater than the cross section of the helium-neon laser beam, the divergence and the transverse dimensions of the beam decreased without affecting the mode structure.