Amplification of scattered induced radiation flux in high-gain laser rods

The spatial distribution of induced radiation flkux within a laser rod is determined through integrated investigations of the angular characteristics of the noisy induced radiation exiting the rod and the angular characteristics of the radiation scattering on its lateral surface. The measurements are made on neodymium activated yttrium aluminum garnet active elements in the form of a rod with a cylindrical surface and plane parallel polished ends. Antireflection coatings were applied to the ends of the elements to reduce reflection to approximately 0.1%. It is demonstrated that closed induced radiant fluxes for which lasing conditions are satisfied can form during strong scattering on the boundaries of the active medium. The stability of these fluxes depends strongly upon their orientation. The most stable fluxes are found to be those which scattered repeatedly at other than mirror angles. The occurrence of a halo of the induced radiation accompanying the occurrence of the generated mode is noted.