Preliminary experimental evidence of anisotropy of turbulence and the effect of non-Kolmogorov turbulence on wavefront tilt statistics

摘要

Abstract: We report preliminary results of wavefront tilt measurements for the star Polaris at the Starfire Optical Range 3.5 m telescope at Kirtland AFB in Albuquerque, NM. We measured full aperture gradient tilt by using five pupil masks representing aperture diameters from 0.1m to 3.5m. Two optical configurations were exploited. In the first configuration, five images of Polaris were recorded simultaneously on one camera frame. The telescope was operated in its normal sidereal pointing mode. In the second configuration, pupil masks were changed sequentially. Additional measurements were collected with the telescope bolted to attempt to mitigate the effects of mont jitter. The coordinate system of the tilt measurement was rotated so that the cross-correlation coefficient between X- and Y-axis tilt components is equal to zero. Several interesting results were obtained. We observed anisotropy of the statistics of wavefront tilt. The observed one-axis tilt variances are unequal and the horizontal tilt variance is consistently greater than the vertical one. We believe these effects dare due to anisotropy of the large evidence of the effects of non-Kolmogorov turbulence on wavefront tilt. The measured tilt variance vs. aperture diameter curve has a knee beyond which the tilt variance no longer decreases for larger diameters. In the low and high frequency range the tilt power spectra obey the f$+$MIN@2/3$/ and f$+$MIN@11/3$/ power law, respectively. The tilt temporal correlation scale for the 3.5m aperture is on the order of 0.4 sec. !16