Thermal blooming threshold computations with a Markov model of velocity turbulence
A model of velocity turbulence based on first order Markov statistics is discussed. The coherence time of the scintillations in the optical intensity of a low power beam passing through the turbulence depends inversely on the root mean square amplitude of the velocity fluctuations. The relationship between coherence time and level of velocity turbulence is independent of both the velocity correlation length and the index structure constant. Application of the Markov model to atmospheric scintillation data yields estimates for the rms amplitude of velocity turbulence consistent with convective boundary layer theory. Computations of the optical field show that velocity turbulence introduces a threshold for stimulated thermal Rayleigh scattering. The threshold can be expressed in terms of a formula relating the limit on absorbed power to the rms amplitude of the velocity fluctuations. Above threshold the instability grows approximately exponentially reaching saturation after only a few waves of phase distortion have accumulated. Below threshold the instability is suppressed but there is a slow increase in the level of index turbulence caused by incoherent heating of the propagation medium. 15 refs., 15 figs.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6285080
- Report Number(s):
- UCID-21589; ON: DE89009709
- Resource Relation:
- Other Information: Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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