Perturbation growth by thermal blooming in turbulence

Journal Article · Fri Jun 01 04:00:00 EDT 1990 · Journal of the Optical Society of America, Part B: Optical Physics; (USA)

DOI:https://doi.org/10.1364/JOSAB.7.001103· OSTI ID:6807170

Karr, T; Morris, J; Chambers, D; Viecelli, J; Cramer, P ^[1]

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1. Lawrence Livermore National Laboratory, P.O. Box 808, L-495, Livermore, California 94550 (US)

The stability of a phase-compensated laser beam propagating in a turbulent absorbing fluid is considered. Small-scale transverse optical perturbations caused by turbulence and noise grow in thermal blooming by two instabilities: the uncompensated stimulated thermal Rayleigh scattering instability and the closed-loop instability. Linearized perturbation theory is used to calculate the electric field spectrum as a Taylor series in time and as a superposition of stable and unstable modes. The method is applicable to fluids with arbitrary parameter variations along the path. Compensated perturbations grow exponentially, and uncompensated ones grow quasi-exponentially. The instability growth rates and the turbulence and noise excitation strengths are derived for a simple fluid with homogeneous parameters. The linearized theory of perturbation growth is in good agreement with numerical simulations of full nonlinear thermal blooming. If the growth rate exceeds the damping rate from other phenomena, then the perturbations grow until they are limited by nonlinear saturation, at which point the beam is significantly degraded. At saturation the laser beam spontaneously breaks into small-scale transverse structures such as filaments or ribbons. The strongest damping mechanism in the open air is typically wind shear, which sets a threshold blooming rate and a threshold absorbed irradiance. Below threshold the perturbations grow linearly; above threshold they grow quasi-exponentially. Other atmospheric damping phenomena, such as diffusion and turbulent mixing, have a smaller effect.

• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 6807170
• Journal Information: Journal of the Optical Society of America, Part B: Optical Physics; (USA), Journal Name: Journal of the Optical Society of America, Part B: Optical Physics; (USA) Vol. 7:6; ISSN JOBPD; ISSN 0740-3224
• Country of Publication: United States
• Language: English

Related Subjects

640410* -- Fluid Physics-- General Fluid Dynamics
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
AIR
EARTH ATMOSPHERE
ELECTROMAGNETIC RADIATION
FLUIDS
GASES
INSTABILITY GROWTH RATES
LASER RADIATION
LIGHT TRANSMISSION
NONLINEAR OPTICS
OPTICAL PROPERTIES
OPTICS
PHYSICAL PROPERTIES
RADIATIONS
REFRACTIVITY
TEMPERATURE EFFECTS
TURBULENCE