Julian Christou (University of California), Szymon Gladyszbd (National University of Ireland), Michael Redfernb (National University of Ireland), L. William Bradford (The Boeing Company), Lewis C. Roberts Jr (The Boeing Company)
Keywords: Adaptive Optics
Abstract:
We have investigated the high-speed temporal variability of the performance of the adaptive optics systems at both the Lick Observatory 3m and the AEOS 3.6m telescopes. Measurements of the instantaneous Strehl ratio for the Lick Observatory data measurements were obtained using the fastsub readout mode of the IRCAL camera. This set up permits high speed focal plane images to be obtained with exposure times of 22ms at a frame rate of ? 20Hz suitable for freezing the compensation under typical K-band (2-2.45µm) observing conditions. Data from the Lick Observatory system has been accumulated over several months with instantaneous Strehl ratios S varying from ? 20%-70% in natural guide star mode.
Data from AEOS is collected by a burst mode capture of 2000 frames of closed-loop wavefront sensor slope data, typically collected at 200Hz (actually exposure time however is much less). The slope data is the residual error after correction by the DM, and this can be used to form an estimate of the Strehl ratio.
These data show that the Strehl ratios can vary considerably over different times scales from seconds to tens of minutes. Under relatively stable conditions, the variability in the instantaneous Strehl ratio ranges for standard deviations of 0.040.08 for mean Strehl ratios of 40%60%. We consistently measure non-Gaussian distributions for S which imply a Gaussian distribution for the instantaneous estimate re of the Fried parameter r0. Although taken at very different time scales and very different technique, the distributions of AEOS Strehl ratios bear a strong resemblance to the distributions of Lick Strehl ratios.
This work has been supported by the National Science Foundation Science and Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement No. AST 9876783 as well as COSMOGRID (Grid-enabled Computational Physics of Natural Phenomena) and the U.S. Air Force Research Laboratorys Directed Energy Directorate under contract (FA9451-05-C-0257 and F29601-00-D-0204).
Date of Conference: September 10-14, 2006
Track: Adaptive Optics