We study the performance of an adaptive optics (AO) system with four laser guide stars (LGSs) and a natural guide star (NGS). The residual cone effect with four LGSs is obtained by a numerical simulation. This method allows the adaptive optics system to be extended toward the visible part of the spectrum without tomographic reconstruction of three-dimensional atmospheric perturbations, resolving the cone effect in the visible. Diffraction-limited images are obtained with 17-arc ms precision in median atmospheric conditions at wavelengths longer than 600 nm. The gain achievable with such a system operated on an existing AO system is studied. For comparison, performance in terms of achievable Strehl ratio is also computed for a reasonable system composed of a 40 × 40 Shack–Hartmann wave-front sensor optimized for the I band. Typical errors of a NGS wave front are computed by use of analytical formulas. With the NGS errors and the cone effect, the Strehl ratio can reach 0.45 at 1.25 μm under good-seeing conditions with the Nasmyth Adaptive Optics System (NAOS; a 14 × 14 subpupil wave-front sensor) at the Very Large Telescope and 0.8 with a 40 × 40 Shack–Hartmann wave-front sensor.
© 2002 Optical Society of America
[Optical Society of America ]
(010.1330) Atmospheric and oceanic optics : Atmospheric turbulence
(010.3310) Atmospheric and oceanic optics : Laser beam transmission
(110.4280) Imaging systems : Noise in imaging systems
(120.5050) Instrumentation, measurement, and metrology : Phase measurement
Elise Viard, Miska Le Louarn, and Norbert Hubin, "Adaptive Optics with Four Laser Guide Stars: Correction of the Cone Effect in Large Telescopes," Appl. Opt. 41, 11-20 (2002)