COAT Measurements and Analysis

: Coherent optical adaptive techniques (COAT) have been studied by experiment, by analysis, and by computer simulation. The experiments have utilized a 21-channel, visible-wavelength, multidither COAT system, while the computer simulations have dealt with both multidither (outgoing-wave) and phase-conjugate (return-wave) systems. Thermal blooming and turbulence distortions and complex-target effects (speckle-modulations) have been studied. This report summarizes the status of the 21-channel DARPA/RADC, visible-wavelength, multidither COAT experimental model and associated hardware and its use in the experimental measurements on this contract. Computer simulation studies of propagation distortion compensation and complex target (speckle) effects are also described. Recommendations are made for future work. Experimental observations with the 21-channel COAT system show that blooming distortions occurring in the first 30% of the focused propagation path can be compensated, leading to roughly a factor of 1.5 increase in peak focused-beam irradians. Depending on the experimental geometry, however, correction factors from 1.0 to 4.0 have been observed. Both experimental and computer simulation results have shown that turbulence compensation performance is not degraded by the presence of thermal blooming, even though little blooming compensation may occur. Experimentally, the addition of tracking and focus controls to 18-channel, planar-array, COAT phase control had no effect for blooming distortions, but produced some correction for an artificially-generated turbulence alone. The 18-channel phase controls could remove essentially 100% of the turbulence distortions in most cases where there was no significant wave-front tilt error.