The Four-Laser Guide Star Facility: Design considerations and system implementation

AbstractGround-based optical telescopes, in particular large ones, require adaptive optics to overcome the atmospheric seeing limit due to turbulence. Correcting the distorted wavefront necessitates bright stars in the field of view. The sky coverage can be greatly increased by using artificial sodium laser guide stars in addition to natural guide stars. We describe the underlying physics and technical considerations relevant to such systems before discussing the design of the four-laser guide star facility (4LGSF) which is currently under development for the ESO Very Large Telescope (VLT) on Cerro Paranal, Chile. The focus is upon the justification of the requirements and their technical solution.

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Statistics of the sodium layer parameters at low geographic latitude and its impact on adaptive-optics sodium laser guide star characteristics

Astronomy and Astrophysics ◽

10.1051/0004-6361/200913281 ◽

2010 ◽

Vol 511 ◽

pp. A31 ◽

Cited By ~ 17

Author(s):

N. Moussaoui ◽

B. R. Clemesha ◽

R. Holzlöhner ◽

D. M. Simonich ◽

D. Bonaccini Calia ◽

...

Keyword(s):

Adaptive Optics ◽

Laser Guide Star ◽

Geographic Latitude ◽

Sodium Layer ◽

Guide Star ◽

Laser Guide ◽

Sodium Laser

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Sodium Laser Guide Star Experiment with a Sum‐Frequency Laser for Adaptive Optics

Publications of the Astronomical Society of the Pacific ◽

10.1086/319327 ◽

2001 ◽

Vol 113 (781) ◽

pp. 366-378 ◽

Cited By ~ 2

Author(s):

Fang Shi

Keyword(s):

Adaptive Optics ◽

Laser Guide Star ◽

Sum Frequency ◽

Star Experiment ◽

Frequency Laser ◽

Guide Star ◽

Laser Guide ◽

Sodium Laser

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High Resolution Imaging Testbed Utilizing Sodium Laser Guide Star Adaptive Optics: The Real Time Wavefront Reconstructor Computer

10.21236/ada523385 ◽

2008 ◽

Author(s):

Richard G. Dekany ◽

Antonin H. Bouchez

Keyword(s):

High Resolution ◽

Real Time ◽

Adaptive Optics ◽

High Resolution Imaging ◽

Laser Guide Star ◽

The Real ◽

Resolution Imaging ◽

Guide Star ◽

Laser Guide ◽

Sodium Laser

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Measuring line-of-sight sodium density structure using laser guide stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa808 ◽

2020 ◽

Vol 494 (2) ◽

pp. 2798-2808

Author(s):

Joschua A Hellemeier ◽

Domenico Bonaccini Calia ◽

Paul Hickson ◽

Angel Otarola ◽

Thomas Pfrommer

Keyword(s):

Adaptive Optics ◽

Continuous Wave ◽

Line Of Sight ◽

Fibre Laser ◽

Modulation Amplitude ◽

Density Structure ◽

Laser Guide Star ◽

Laser Guide Stars ◽

Guide Star ◽

Laser Guide

ABSTRACT The performance of adaptive optics systems employing sodium laser guide stars can be improved by continuously monitoring the vertical density structure of mesospheric sodium along the line of sight. We demonstrate that sodium density profiles can be retrieved by amplitude modulation of continuous wave (CW) lasers. In an experiment conducted at the Large Zenith Telescope (LZT), ESO’s Wendelstein Raman-fibre laser was amplitude-modulated with a pseudo-random binary sequence and profiles were obtained by cross-correlation of the modulation pattern with the observed return signal from the laser guide star. For comparison, high-resolution profiles were obtained simultaneously using the lidar system of the LZT. The profiles obtained by the two techniques show noise contamination, but were found to agree to within the measurement error. As a further check, a comparison was also made between several lidar profiles and those obtained by simultaneous observations using a remote telescope to image the laser plume from the side. The modulated CW lidar technique could be implemented by diverting a small fraction of the returned laser light to a photon counting detector. Theoretical analysis and numerical simulations indicate that, for 50 per cent modulation strength, the sodium centroid altitude could be retrieved every 5 s from a single laser guide star, with an accuracy which would induce a corresponding wavefront error of 50 nm for the Extremely Large Telescope and less than 30 nm for the Thirty Meter Telescope and Giant Magellan Telescope. If multiple laser guide stars are employed, the required modulation amplitude will be smaller.

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