Effect of power losses on self-focusing of high-intensity laser beam in gases

A theoretical study of power loss from periphery of an ultrashort pulse laser beam and temporally resolved defocusing produced by laser-induced plasma are performed using paraxial approximation. Our analysis incorporates consideration of spatial distribution of the laser beam irradiance and the results show that substantial power losses (10-80%) occur from the beam periphery limiting the length of a filament. It was also shown that the generally accepted concept of self-focusing critical power is inconsistent with consideration of self-induced refraction of spatially distributed laser beam. A new criterion for self-focusing and hypothesis for multiple filamentation are proposed.