Eric James

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.

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).

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.

The Gemini MCAO bench: system overview and lab integration

We present Canopus, the AO bench for Geminis 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 RTC.

GeMS: Gemini Mcao System: current status and commissioning plans

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 view. 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.

DEIMOS: a wide-field faint-object spectrograph

This paper describes the design of DEIMOS -- a dual beam, off axis, multi object spectrograph of medium resolution, being designed for the Keck II telescope on Mauna Kea in Hawaii. The difficult and advanced scientific goals of the DEIMOS project have generated many challenging design requirements. The DEIMOS team at Lick Observatory has been responding to these challenges with new and unique concepts in instrument design and fabrication.

Design considerations of the AO module for the Gemini South multiconjugate adaptive optics system

The adaptive optics system for the Gemini South telescope, currently in the design phase, consists of several major subsystem. The largest subsystem, called the AO module, contains most of the optics and electronics and is mounted on one of the Cassegrain instrument ports. The initial system will be a conventional laser guide star AO system, but the plan is to eventually expand it to a multi-conjugate system. The system is being designed to readily add the components necessary to upgrade to a multi-conjugate system. This paper describes the design challenges encountered and solutions that were derived for the AO module design. The complexity of the multi-conjugate version is illustrated, including optical, mechanical, electronic and controls issues.

Design update of DEIMOS: a wide-field faint-object spectrograph

DEIMOS is a dual beam, off axis, multi object spectrograph of medium resolution being designed for the Keck II Telescope on Mauna Kea in Hawaii. The difficult an advanced scientific goals of the DEIMOS project have generated many challenging design requirements. The DEIMOS team at Lick Observatory has been responding to these challenges with new and unique concepts in instrument design and fabrication. This paper is an update to the paper presented at the SPIE conference in Landskrona, Sweden in 1996.

Elastomeric lens mounts

Instruments for large telescopes often require cameras with large, deeply-curved, and temperature-sensitive lenses. The instrument error budgets require each lens to be supported so that excellent performance is maintained in the face of gravitational and thermal perturbations. We describe here elastomeric mounts that address these requirements. We first describe the general design principles, the effects of errors in design and fabrication, and the performance under static and dynamic loads. We describe specific examples; the elastomer RTV560 and the lens supports for the camera of the W. M. Keck Observatory DEIMOS spectrograph.