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High-Resolution Imaging with a Tip-Tilt Cassegrain Secondary
L. M. Close and D. W. McCarthy, Jr.
Publications of the Astronomical Society of the Pacific
Vol. 106, No. 695 (1994 January), pp. 77-86
Published by: Astronomical Society of the Pacific
Stable URL: http://www.jstor.org/stable/40680244
Page Count: 10
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A prototype adaptive secondary mirror has been developed on a 2.3-m telescope to stabilize rapid image motion caused by atmospheric turbulence. The instantaneous position of an image's centroid, or brightest speckle, is measured by a near-infrared camera system which enables the tip-tilt mirror to recenter the image. Correction is accomplished at closed-loop frequencies of ≤100 Hz on guide stars with (2.2 μm) magnitudes ≤8. Image motion is reduced to <0.̋1 rms, removing over 90% of low-frequency (f≤5 Hz) tilt power, leaving ≤1 rad² mean square wave front tilt phase error. In seeing conditions where D/r₀ ~ 4, long exposures in the H band (1.6 μm) exhibit a nearly diffraction-limited resolution of 0? 19 FWHM (Strehl ratio ~0.14)— a factor of 4 improvement over uncorrected images. Reduction of the present static optical errors will improve the Strehl ratio another factor of 2, leading to ~ 70% of the maximum possible Strehl ratio.
Publications of the Astronomical Society of the Pacific © 1994 The University of Chicago Press