Near-Infrared Tip-Tilt Sensor for Laser Guide Star Adaptive Optics

California Association For Research In Astronomy, Kamuela HI

Investigators

Abstract

The goal of correcting the Earth's atmospheric effects on astronomical images has seen considerable success through the use of laser guide star adaptive optics (AO) systems that provide a quantitative measure of the turbulence distributed over the aperture of a large telescope. However, laser systems by themselves cannot detect the ensemble shift in an object's image that is induced by the atmosphere, and the encircled energy in a diffraction-limited spot could be increased by more than 40% if this correction were made. Such a "tip/tilt" correction is only available through the use of a natural guide star - a rather bright natural star included in the telescope field of view - in tandem with the laser projection system. The near-IR tip/tilt sensor being constructed by Dr. Peter Wizinowich and collaborators of the California Association for Research in Astronomy for the Keck 10-m telescope on Mauna Kea, Hawaii will accomplish this goal. By working in the K (2.2 micron wavelength) atmospheric transmission band, the planned system will provide high bandwidth (up to 1 kHz) tip/tilt information using one to three stars in a 2 arcminute diameter area, and enable corrections over that entire field of view. Additionally, focus corrections are available at a much higher time resolution than for standard schemes. The Keck telescopes are arguably the most advanced, reliable, and scientifically productive large-telescope AO systems available anywhere in the world. Scientists and technical staff at the managing institutions are among the most capable in the world, and the mountaintop is an outstanding observing site. Up to 30% of observing time is available to the general community through various means, so improvements in the imaging capabilities of the telescopes through mechanisms like near-IR tip/tilt correction systems benefit all of U.S. astronomy. Funding for this work is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.