In the construction phase since 2014, the Large Synoptic Survey Telescope (LSST) is an 8.4 meter diameter wide-field (3.5 degrees) survey telescope located on the summit of Cerro Pachón in Chile. The reflective telescope uses an 8.4 m f/1.06 concave primary, an annular 3.4 m meniscus convex aspheric secondary and a 5.2 m concave tertiary. The primary and tertiary mirrors are aspheric surfaces figured from a monolithic substrate and referred to as the M1M3 mirror. This unique design offers significant advantages in the reduction of degrees of freedom, improved structural stiffness for the otherwise annular surfaces, and enables a very compact design. The three-mirror system feeds a threeelement refractive corrector to produce a 3.5 degree diameter field of view on a 64 cm diameter flat focal surface. This paper describes the current status of the mirror system components and provides an overview of the upcoming milestones including the mirror coating and the mirror system integrated tests prior to summit integration.
Since 2004 the Gemini telescopes have used a protected 4-layer silver coating on their 8-meter diameter primary mirror and other smaller optics. Protected silver was chosen for the twin telescopes due to its high reflectivity and low emissivity properties. For over 10 years the protected 4-layer silver coating at Gemini exceeded the science requirements for reflectivity of 88% between 0.4-0.7 μm and 84% between 0.7-1.1 μm. Initial durability requirements that the coating should last at least two years have been also been surpassed. All mirrors have met the durability requirement, with most outlasting it significantly. Provided is a ten year retrospective on the progress in the use and maintenance of 4-layer silver coatings on large astronomical optics.
The Gemini Multi-conjugate adaptive optics System (GeMS) at the Gemini South telescope in Cerro Pachon is the first sodium Laser Guide Star (LGS) adaptive optics (AO) system with multiple guide stars. It uses five LGSs and two deformable mirrors (DMs) to measure and compensate for distortions induced by atmospheric turbulence. After its 2012 commissioning phase, it is now transitioning into regular operations. Although GeMS has unique scientific capabilities, it remains a challenging instrument to maintain, operate and upgrade. In this paper, we summarize the latest news and results. First, we describe the engineering work done this past year, mostly during our last instrument shutdown in 2013 austral winter, covering many subsystems: an erroneous reconjugation of the Laser guide star wavefront sensor, the correction of focus field distortion for the natural guide star wavefront sensor and engineering changes dealing with our laser and its beam transfer optics. We also describe our revamped software, developed to integrate the instrument into the Gemini operational model, and the new optimization procedures aiming to reduce GeMS time overheads. Significant software improvements were achieved on the acquisition of natural guide stars by our natural guide star wavefront sensor, on the automation of tip-tilt and higher-order loop optimization, and on the tomographic non-common path aberration compensation. We then go through the current operational scheme and present the plan for the next years. We offered 38 nights in our last semester. We review the current system efficiency in term of raw performance, completed programs and time overheads. We also present our current efforts to merge GeMS into the Gemini base facility project, where night operations are all reliably driven from our La Serena headquarter, without the need for any spotter. Finally we present the plan for the future upgrades, mostly dedicated toward improving the performance and reliability of the system. Our first upgrade called NGS2, a project lead by the Australian National University, based a focal plane camera will replace the current low throughput natural guide wavefront sensor. On a longer term, we are also planning the (re-)integration of our third deformable mirror, lost during the early phase of commissioning. Early plans to improve the reliability of our laser will be presented.
The Gemini Multi-Conjugate Adaptive Optics System (GeMS) began its on-sky commissioning in January 2011.
The system provides high order wide field corrections using a constellation of five Laser Guide Stars. In December 2011, commissioning culminated in images with a FWHM of 80±2mas at 1.65 microns (H band) over an 87 x 87 arcsecond field of view. The first images have already demonstrated the scientific potential of GeMS, and after more than a year of commissioning GeMS is finally close to completion and ready for science. This paper presents a general status of the GeMS project and summarizes the achievements made during more than a year of commissioning. The characterization of GeMS performance is presented in a companion paper: “GeMS on-sky results”, Rigaut et al. Here we report on the sub-systems' performance, discuss current limitations and present proposed upgrades. The integration of GeMS into the observatory operational scheme is detailed. Finally, we present the plans for next year's operations with GeMS.
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.
With two to three deformable mirrors, three Natural Guide Stars (NGS) and five sodium Laser Guide Stars (LGS), the
Gemini Multi-Conjugate Adaptive Optics System (Gemini MCAO a.k.a. GeMS) will be the first facility-class MCAO
capability to be offered for regular science observations starting in 2013A. The engineering and science commissioning
phase of the project was kicked off in January 2011 when the Gemini South Laser Guide Star Facility (GS LGSF)
propagated its 50W laser above the summit of Cerro Pachón, Chile. GeMS commissioning has proceeded throughout
2011 and the first half of 2012 at a pace of one 6- to 10-night run per month with a 5-month pause during the 2011
This paper focuses on the LGSF-side of the project and provides an overview of the LGSF system and subsystems, their
top-level specifications, design, integration with the telescope, and performance throughout commissioning and beyond.
Subsystems of the GS LGSF include: (i) a diode-pumped solid-state 1.06+1.32 micron sum-frequency laser capable of
producing over 50W of output power at the sodium wavelength (589nm); (ii) Beam Transfer Optics (BTO) that transport
the 50W beam up the telescope, split the beam five-ways and configure the five 10W beams for projection by the Laser
Launch Telescope (LLT) located behind the Gemini South 8m telescope secondary mirror; and (iii) a variety of safety
systems to ensure safe laser operations for observatory personnel and equipment, neighbor observatories, as well as
passing aircrafts and satellites.
The Gemini Multi-Conjugate Adaptive Optics System (GeMS} began its on-sky commissioning in January 20ll. The system provides high order wide-field corrections using a constellation of five Laser Guide Stars. In December 20ll, commissioning culminated in images with a FWHM of 80±2mas at 1.65 microns (H band} over an 87 x 87 arcsccond field of view. The first images have already demonstrated the scientific potential of GeMS, and after more than a year of commissioning GeMS is finally close to completion and ready for science. This paper presents a general status of the GeMS project and summarizes the achievements made during more than a year of commissioning. The characterization of GeMS performance is presented in a companion paper: "GeMS on-sky results" , R.igaut ct al. Here we report on the sub-systems' performance, discuss current limitations and present proposed upgrades. The integration of GeMS into the observatory operational scheme is detailed. Finally, we present the plans for next year's operations with GeMS.
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.
As part of its Safe Aircraft Localization and Satellite Acquisition System (SALSA), Gemini is building an All Sky Camera (ASCAM) system to detect aircrafts in order to prevent propagation of the laser that could be a safety hazard for pilots and passengers. ASCAM detections, including trajectory parameters, are made available to neighbor observatories so they may compute impact parameters given their location. We present in this paper an overview of the system
architecture, a description of the software solution and detection algorithm, some performance and on-sky result.
We present Canopus, the AO bench for Gemini's Multi Conjugate Adaptive Optics System (GEMS), a unique facility for
the Gemini South telescope located at Cerro Pachon in Chile. The MCAO system uses five laser beacons in conjunction
with different natural guide stars configurations. A deployable fold mirror located in the telescope Acquisition and
Guiding Unit (A&G) sends the telescope beam to the entrance of the bench. The beam is split within Canopus into three
main components: two sensing paths and the output corrected science beam. Light from the laser constellation (589nm)
is directed to five Shack-Hartman wave front sensors (E2V-39 CCDs read at 800Hz). Visible light from natural guide
stars is sent to three independent sensors arrays (SCPM AQ4C Avalanche Photodiodes modules in quad cell
arrangement) via optical fibers mounted on independent stages and a slow focus sensor (E2V-57 back-illuminated
CCD). The infrared corrected beam exits Canopus and goes to instrumentation for science. The Real Time Controller
(RTC) analyses wavefront signals and correct distortions using a fast tip-tilt mirror and three deformable mirrors
conjugated at different altitudes. The RTC also adjusts positioning of the laser beacon (Beam Transfer Optics fast
steering array), and handles miscellaneous offloads (M1 figure, M2 tip/tilt, LGS zoom and magnification corrections,
NGS probes adjustments etc.). Background optimizations run on a separate dedicated server to feed new parameters into
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.
The Gemini twins were the first large modern telescopes to receive protected silver coatings on their
mirrors in 2004. The low emissivity requirement is fundamental for the IR optimization. In the mid-IR a
factor of two reduction in telescope emissivity is equivalent to increasing the collecting area by the same
factor. Our emissivity maintenance requirement is very stringent: 0.5% maximum degradation during
operations, at any single wavelength beyond 2.2 μm.
We developed a very rigorous standard to wash the primary mirrors in the telescope without science
down time. The in-situ washes are made regularly, and the reflectivity and emissivity gains are significant.
The coating lifetime has been extended far more than our original expectations. In this report we describe the
in-situ process and hardware, explain our maintenance plan, and show results of the coating performance over
The Gemini Multi-Conjugate Adaptive Optics project was launched in April 1999 to become the Gemini South
AO facility in Chile. The system includes 5 laser guide stars, 3 natural guide stars and 3 deformable mirrors optically
conjugated at 0, 4.5 and 9km to achieve near-uniform atmospheric compensation over a 1 arc minute square field of
Sub-contracted systems with vendors were started as early as October 2001 and were all delivered by July
2007, but for the 50W laser (due around September 2008). The in-house development began in January 2006, and is
expected to be completed by the end of 2008 to continue with integration and testing (I&T) on the telescope. The on-sky
commissioning phase is scheduled to start during the first half of 2009.
In this general overview, we will first describe the status of each subsystem with their major requirements, risk
areas and achieved performance. Next we will present our plan to complete the project by reviewing the remaining steps
through I&T and commissioning on the telescope, both during day-time and at night-time. Finally, we will summarize
some management activities like schedules, resources and conclude with some lessons learned.
The Gemini twins were the first large modern telescopes to receive protected Silver coatings on their mirrors in 2004.
We report the performance evolution of these 4-layer coatings in terms of reflectivity and emissivity. We evaluate the
durability of these thin films by comparison to the evolution of some samples that we have produced and exposed since
2002. Finally, we will explain our maintenance plan.
The Large Synoptic Survey Telescope (LSST) baseline design includes aluminum coating for the large mirrors in its 3 element modified Paul Baker optical design. The 8.4 meter diameter of the primary provides a significant challenge to the LSST coating plans however such coatings have successfully achieved for this size aperture. LSST also recognizes that the use of mirror coatings with higher reflectivity and durability would significantly benefit its science by increasing its overall throughput and improving its operational efficiency. LSST has identified Lawrence Livermore National Laboratory (LLNL) blue-shifted protected silver coating as a possible candidate to provide this blue wavelength performance. A study has been started to assess the performance of these and other coatings in the observatory environment. We present the details of this ongoing program, the results obtained so far, and related coating tests results. LSST has also engaged in collaboration with the Gemini Telescope in the development and testing of an Al-Ag coating based on their current recipe. The first results of these tests are also included in this report.
Besides the increasing use of adaptive optics (AO) on modern telescopes, active optics (aO) are still of high importance to optimize Image Quality (IQ) for non-AO instruments and decrease the dynamic range needed for AO corrections. We will describe the design and operation of an optical alignment bench used to calibrate the aO models of the peripheral wavefront sensors. This setup is used to determine optical models in stable conditions in the laboratory and thus optimize wavefront correction on the sky. We will show results of this technique applied to our 2x2 Shack-Hartmann wavefront sensor used for tip-tilt-focus-astigmatism correction of all our non-AO instruments. We will also review some sub-systems performance monitoring tools and finally gauge the performance of active optics on the Gemini telescopes by analyzing the delivered image quality for various instruments.
The Gemini telescopes were designed to be infrared-optimized. Among the features specified for optimal performance is the use of silver-based coatings on the mirrors. The feasibility study contracted by Gemini in 1994-1995 provided both techniques and recipes to apply these high-reflectivity and low-emissivity films. All this effort is now being implemented in our coating plants. At the time of the study, sputtering experiments showed that a reflectivity of 99.1% at 10μm was achievable. We have now produced bare and protected silver sputtered films in our coating plants and conducted environmental testing, both accelerated and in real-life conditions, to assess the durability. We have also already applied, for the first time ever, protected-silver coatings on the main optical elements (M1, M2 and M3) of an 8-m telescope. We report here the progress to date, the performance of the films, and our long-term plans for mirror coatings and maintenance.