Experimental measurement of tilt correlation with higher-order modes in the time domain for turbulence-induced phase aberrations: implications to airborne laser beam steering

摘要

Abstract: Theoretical analysis of the temporal cross-correlation properties of turbulence-induced phase aberrations predict that while tilt is uncorrelated with most higher-order modes at zero time delay, the magnitude of the cross-correlation increases through some maximum value before going to zero at long time delays. To test this theoretical prediction, we employ laboratory measurements of phase induced on a laser beam propagating through a channeled flow of turbulent gas. From these measurements, the temporal cross-correlation of various aberration modes was estimated. Theoretical expressions were derived for these cross-correlations, and the results of these calculations agree well with experimental measurements. Both the experimental and the theoretical results demonstrate that the magnitude of cross- correlation between tilt and higher-order modes is non-zero over a range of temporal delay. Thus, higher-order model measurements may be incorporated into an optimal estimator for tilt, enhancing estimator performance.!18