Experiments to Assess the Effectiveness of Multiple Laser Guide Stars for Adaptive Optics.

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Session 42 -- High-Spatial Resolution
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

[42.01] Experiments to Assess the Effectiveness of Multiple Laser Guide Stars for Adaptive Optics.

C. Neyman, L. Thompson (University of Illinois at Urbana-Champaign)

Adaptive optics systems have been shown to provide a remarkable increase in resolution and sensitivity for ground- based optical and near-IR telescopes. Previously classified work by the DOD has provided proof of the laser guide star (LGS) concept for correcting telescopes. The ideal artificial reference is a plane wave which probes the atmospheric distortion with a wavefront identical to that of a star at infinity. However, a LGS is created at some finite distance above the telescope in the atmosphere and its wavefront is spherical. As a result a LGS does not correctly sample the atmospheric distortion. This sampling error is called focus anisoplanatism. Focus anisoplanatism sets a fundamental limit on the ability of a single LGS adaptive optic system to correct seeing. This effect limits the largest aperture that can be corrected at visible wavelengths by a single Rayleigh guide star to about 1m and a single sodium LGS to about 3m. A solution to focus anisoplanatism is to create an array of multiple laser stars each being used to correct a small area of the telescope pupil directly under that LGS. This reduces the focus anisoplanatism to acceptable levels. As a prelude to using multiple laser guide stars in our system at Mt. Wilson (UnISIS) we are conducting experiments at the Mt. Laguna Observatory 1m telescope. These experiments involve projecting two laser guide stars. The experiment measures the relative beacon wander for various broadcast and reception geometries of the LGS. These experiments will help assess the feasibility of the multiple laser guide star concept. Implications of these experiments on a finished system will be presented.

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