Charles Yee, Lawrence Lesyna, Kenneth Lorell, Jean-Noel Aubrun, Pat Champagne, Neal Didriksen, Victor Nikolaskin, Roger Mihara, Robert Clappier, Ramji Digumarthi
An engineering test unit Fabry-Perot interferometer has been designed and built to operate in the 1.5-1.7 um regime from room temperature to 30 K°. The Fabry-Perot interferometer is tuned by controlling the gap spacing between the two highly reflecting mirrors. Capacitance sensors are used to control the gap spacing and maintain parallelism of the mirrors. An overview of the optical, mechanical, electrical, and control designs of the instrument are described. Some early results at cryogenic temperature indicative of the performance of the instruments are presented.
High power laser propagation through the turbulent atmospheric is difficult due to thermal blooming effects. Current atmospheric turbulence models assume that the turbulent structure is transported across the laser beam diameter at the mean wind speed. This frozen turbulence model is valid if the laser length is short compared to the characteristic time scale associated with the evolution of the turbulence. However, for laser systems with very long inter-pulse spacing, the turbulent structure may have sufficient time to evolve dynamically between laser pulses. The turbulent structure early in the pulse train may be quite different from the turbulent structure late in the pulse train. In this study, the results from a two dimensional code used to model the time evolution of atmospheric turbulence are presented. Calculations of the turbulent diffusion and the auto-correlation time of the turbulence as a function of eddy size and velocity structure constant are also given.
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