Céline d'Orgeville

Gemini multiconjugate adaptive optics system review - I. Design, trade-offs and integration

The Gemini multiconjugate adaptive optics system (GeMS) at the Gemini South telescope in Cerro Pachon is the first sodium-based multilaser guide star (LGS) adaptive optics system. It uses five LGSs and two deformable mirrors to measure and compensate for atmospheric distortions. The GeMS project started in 1999, and saw first light in 2011. It is now in regular operation, producing images close to the diffraction limit in the near-infrared, with uniform quality over a field of view of two square arcminutes. This paper is the first one in a two-paper review of GeMS. It describes the system, explains why and how it was built, discusses the design choices and trade-offs, and presents the main issues encountered during the course of the project. Finally, we briefly present the results of the system first light.

Gemini multiconjugate adaptive optics system review – II. Commissioning, operation and overall performance

The Gemini Multi-conjugate Adaptive Optics System - GeMS, a facility instrument mounted on the Gemini South telescope, delivers a uniform, near di↵raction limited images at near infrared wavelengths (0.95 µm - 2.5 µm) over a field of view of 120 00 . GeMS is the first sodium layer based multi laser guide star adaptive optics system used in astronomy. It uses five laser guide stars distributed on a 60 00 square constellation to measure for atmospheric distortions and two deformable mirrors to compensate for it. In this paper, the second devoted to describe the GeMS project, we present the commissioning, overall performance and operational scheme of GeMS. Performance of each sub-system is derived from the commissioning results. The typical image quality, expressed in full with half maximum, Strehl ratios and variations over the field delivered by the system are then described. A discussion of the main contributor to performance limitation is carried-out. Finally, overheads and future system upgrades are described.

Laser guide star upgrade of Altair at Gemini North

Altair is the general-purpose Adaptive Optics bench installed on Gemini North that has operated successfully with Natural Guide Star (NGS) since 2003. The original design and fabrication included an additional WaveFront Sensor (WFS) to enable operation with Laser Guide Star (LGS). Altair has been recently upgraded and functional commissioning was performed between June and November 2005. The insertion of a dichroic beamsplitter in the NGS path allows to reflect the 589nm light to the LGS wavefront sensor and transmit the visible light of the NGS (or Tip-Tilt Guide star -TTGS-) to the tip-tilt-focus sensors. We will review the various modifications made for this dual operation, both in hardware and software, and describe the steps and results of the integration and testing phase on the sky.

MCAO for Gemini South

The multi-conjugate adaptive optics (MCAO) system design for the Gemini-South 8-meter telescope will provide near-diffraction-limited, highly uniform atmospheric turbulence compensation at near-infrared wavelengths over a 2 arc minute diameter field-of-view. The design includes three deformable mirrors optically conjugate to ranges of 0, 4.5, and 9.0 kilometers with 349, 468, and 208 actuators, five 10-Watt-class sodium laser guide stars (LGSs) projected from a laser launch telescope located behind the Gemini secondary mirror, five Shack-Hartmann LGS wavefront sensors of order 16 by 16, and three tip/tilt natural guide star (NGS) wavefront sensors to measure tip/tilt and tilt anisoplanatism wavefront errors. The WFS sampling rate is 800 Hz. This paper provides a brief overview of sample science applications and performance estimates for the Gemini South MCAO system, together with a summary of the performance requirements and/or design status of the principal subsystems. These include the adaptive optics module (AOM), the laser system (LS), the beam transfer optics (BTO) and laser launch telescope (LLT), the real time control (RTC) system, and the aircraft safety system (SALSA).

GeMS: first on-sky results

GeMS, the Gemini Laser Guide Star Multi-Conjugate Adaptive Optics facility system, has seen first light in December 2011, and has already produced images with H band Strehl ratio in excess of 35% over fields of view of 85x85 arcsec, fulfilling the MCAO promise. In this paper, we report on these early results, analyze trends in performance, and concentrate on key or novel aspects of the system, like centroid gain estimation, on-sky non common path aberration estimation. We also present the first astrometric analysis, showing very encouraging results.

The Gemini MCAO System GeMS: nearing the end of a lab-story

GeMS (the Gemini Multi-conjugated adaptive optics System) is a facility instrument for the Gemini-South telescope. It will deliver a uniform, diffraction-limited image quality at near-infrared (NIR) wavelengths over an extended FoV or more than 1 arcmin across. GeMS is a unique and challenging project from the technological point of view and because of its control complexity. The system includes 5 laser guide stars, 3 natural guide stars, 3 deformable mirrors optically conjugated at 0, 4.5 and 9km and 1 tip-tilt mirror. After 10 years since the beginning of the project, GeMS is finally reaching a state in which all the subsystems have been received, integrated and, in the large part, tested. In this paper, we report on the progress and current status of the different sub-systems with a particular emphasis on the calibrations, control and optimization of the AO bench.

Gemini north and south laser guide star systems requirements and preliminary designs

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 Pachon, 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 on-going 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.

Characterization of the sodium layer at Cerro Pachon, and impact on laser guide star performance

Detailed knowledge of the mesopheric sodium layer characteritics is crucial to estimate and optimize the performance of Laser Guide Star (LGS) assisted Adaptive Optics (AO) systems. In this paper, we present an analysis of two sets of data on the mesospheric sodium layer. The first set comes from a laser experiment that was carried out at Cerro Tololo to monitor the abundance and altitude of the mesospheric sodium in 2001, during six runs covering a period of one year. This data is used to derive the mesospheric sodium column density, the sodium layer thickness and the temporal behavior of the sodium layer mean altitude. The second set of data was gathered during the first year of the Gemini MCAO System (GeMS) commissioning and operations. GeMS uses five LGS to measure and compensate for atmospheric distortions. Analysis of the LGS wavefront sensor data provides information about the sodium photon return and the spot elongation seen by the WFS. All these parameters show large variations on a yearly, nightly and hourly basis, affecting the LGS brightness, shape and mean altitude. The sodium photon return varies by a factor of three to four over a year, and can change by a factor of two over a night. In addition, the comparison of the photon returns obtained in 2001 with those measured a decade later using GeMS shows a significant difference in laser format efficiencies. We find that the temporal power spectrum of the sodium mean altitude follows a linear trend, in good agreement with the results reported by Pfrommer & Hickson (2010).

The giant magellan telescope laser tomography adaptive optics system

The Giant Magellan Telescope presents a unique optical design with seven 8.4 m diameter primary mirrors matched by seven adaptive secondary mirrors (ASM). The ASMs can be controlled in several dierent Adaptive Optics (AO) observing modes coupled to the telescope . One of these AO systems, the Laser Tomography Adaptive Optics (LTAO) system is currently in its preliminary design phase. The LTAO observing mode will provide a Strehl ratio in H band of at least 30% over more than 20% of the sky and an ensquared energy in K band of at least 40% in a 50 milli-arcsec spaxel over more than 50% of the sky. To achieve its performance requirements, the LTAO observing mode uses six 20W Laser Guide Stars (LGS) with six order-60x60 Shack-Hartmann wavefront sensors. The LGSs are launched from three locations at the periphery of the telescope primaries. A natural guide star (NGS) is used separately to measure tip-tilt, focus and low-bandwidth-low-order aberrations, as well as telescope segment piston. An open-loop controlled deformable mirror corrects the o-axis NGS infrared wavefront. We give an update on the design of the LTAO WFSs, the LGS facility, the on-instrument wavefront sensors and the tomography and control algorithms.

The Gemini South MCAO laser guide star facility: getting ready for first light

The Gemini Observatory is in the final integration and test phase for its Multi-Conjugate Adaptive Optics (MCAO) project at the Gemini South 8-meter telescope atop Cerro Pachón, Chile. This paper presents an overview and status of the laser-side of the MCAO project in general and its Beam Transfer Optics (BTO), Laser Launch Telescope (LLT) and Safety Systems in particular. We review the commonalities and differences between the Gemini North Laser Guide Star (LGS) facility producing one LGS with a 10W-class laser, and its southern sibling producing five LGS with a 50W-class laser. We also highlight the modifications brought to the initial Gemini South LGS facility design based on lessons learned over 3 years of LGS operations in Hawaii. Finally, current integration and test results of the BTO and on-sky LLT performance are presented. Laser first light is expected in early 2009.