Abstract

Spatial variations of a laser beam propagating in an absorbing medium are amplified by stimulated thermal Rayleigh scattering. Small perturbations of wavelength Λ on a beam of optical wavelength λ and path length z are predicted to grow asymptotically ~exp[(tz)^1/2] for Λ << (λz)^1/2 and ~exp{[tz(λz/Λ²)]^1/3} for Λ >> (λz)^1/2. The principal damping mechanisms are thermal diffusion, inhomogeneous convection, and turbulent mixing of the medium. When growth exceeds damping, small perturbations, either seeded or from noise, grow in time and space until they are comparable to the unperturbed beam.

© 1989 Optical Society of America