Accession Number : AD0720311
Title : Thermal Blooming of Laser Beams in Gases.
Descriptive Note : Final rept.,
Corporate Author : NAVAL RESEARCH LAB WASHINGTON D C
Personal Author(s) : Hayes,J. N.
Report Date : 11 FEB 1971
Pagination or Media Count : 37
Abstract : The trajectories of light rays and the intensity pattern of a laser beam as a function of time and of distance down the beam are determined. It is assumed in this calculation that (a) the medium is a homogeneous, isotropic, and initially quiescent gas, (b) convection, viscosity, and thermal conduction may be ignored at early times, (c) changes in total beam power as a function of distance downbeam may be ignored, (d) a specific model of energy deposition is valid, (e) the medium may be described by equations of hydrodynamics and thermodynamics and obeys the Lorentz-Lorenz Law, and (f) geometrical optics applies to the problem. It is shown that this model can be solved exactly; long- and short-time behavior of the solutions is discussed, and the times for the onset of convection are estimated. The phenomenon of laser defocusing is shown to change rapidly with time; a definition of thermal blooming is given, and it is shown that the region of blooming moves up the beam toward the face of the laser. The intensity pattern at a fixed point in space is shown to change its profile, going over to a bright narrow annular ring whose radius increases with the passage of time. Parameter combinations required for studies of various aspects of the blooming phenomenon are pointed out as the mathematical development progresses. (Author)
Descriptors : (*LASERS, LIGHT TRANSMISSION), FOCUSING, INTENSITY, INTERACTIONS, PARTIAL DIFFERENTIAL EQUATIONS, INTEGRAL TRANSFORMS, GASES, ATMOSPHERES
Subject Categories : Lasers and Masers
Distribution Statement : APPROVED FOR PUBLIC RELEASE