<title>Gemini north and south laser guide star systems requirements and preliminary designs</title>

Abstract

In the near future, the Gemini Observatory will offer Laser Guide Star Adaptive Optics (LGS AO) observations on both Gemini North and South telescopes. The Gemini North AO system will use a 10W-class sodium laser to produce one laser guide star at Mauna Kea, Hawaii, whereas the Gemini South AO System will use up to five such lasers or a single 50W-class laser to produce one to five sodium beacons at Cerro Pachón, Chile. In this paper we discuss the similarities and differences between the Gemini North and South Laser Guide Star Systems. We give a brief overview of the Gemini facility Adaptive Optics systems and the ongoing laser research and development program to procure efficient, affordable and reliable lasers. The main part of the paper presents the top-level requirements and preliminary designs for four of the Gemini North and South Laser Guide Star subsystems: the Laser Systems (LS), Beam Transfer Optics (BTO), Laser Launch Telescopes (LLT), and their associated Periscopes.

MCAO for Gemini South

“…Depending on mesospheric sodium column density (2-3 10 9 atoms/cm 2 ), zenith angle (0-45°), and other assumptions, the total laser power requirement will be in the 50W range for continuous-wave (CW), CW-modelocked, and 800Hz-macro-micro pulsed laser formats. 11,12 The use of pulsed lasers with an 800Hz repetition rate that enables time-gating of Rayleigh scattered light on the LGS WFS would certainly increase the MCAO system's overall performance and enable operation with subvisible cirrus present, but CW and CWmode-locked lasers have not been ruled out at this time. Other temporal formats that are less efficient in exciting mesospheric sodium atoms will most likely require too high an output power to be seriously considered for the MCAO laser.…”

“…12 A year ago, reference 12 gave an overview of the on-going Gemini laser Research and Development (R&D) program, and reported on three risk-reduction activities initiated in collaboration with the US Air Force and the Center for Adaptive Optics (CfAO). The diode-pumped solid-state laser R&D programs initiated by Gemini and others are now bearing fruits.…”

Development of all-solid-state coherent 589 nm light source: toward the realization of sodium lidar and laser guide star adaptive optics

“…Beam quality should be TEM 00 for control of spot size on the sodium layer at 90 km altitude. 12,13 In…”

“…12,15,16,18 On the other hand, single longitudinal mode and pulsed operation is required for precise tracing of the sodium absorption depend on temperature 16 16,17 And sodium D 2 resonance light sources constructed with all-solid-state lasers 12,13,[18][19][20] or fiber lasers 21,22 is suitable for stable operation in LGS AO and sodium lidar.…”

An efficient modeless laser for a mesospheric sodium laser guide star

“…In 2004 the Gemini North Telescope will be equipped with a 20 W laser that frequency sums two picosecond YAG lasers (500 ps), pumped by diode lasers 10 . Several new 589 nm laser sources are under study.…”