AO systems aim at detecting and correcting for optical distortions induced by atmospheric turbulences. They are also extremely sensitive to extraneous sources of perturbation such as vibrations, which degrade the performance. The Gemini South telescope has currently two main AO systems: the Gemini Multi Conjugated AO System GeMS and the Gemini Planet Imager GPI. GeMS is operational and regularly used for science observation delivering close to diffraction limit resolution over a large field of view (85×85 arcsec2). Performance limitation due to the use of an integrator for tip-tilt control is here explored. In particular, this type of controller does not allow for the mitigation of vibrations with an arbitrary natural frequency. We have thus implemented a tip-tilt Linear Quadratic Gaussian (LQG) controller with different underlying perturbation models: (i) a sum of autoregressive models of order 2 identified from an estimated power spectrum density (s-AR2) of the perturbation,1 already tested on CANARY2 and routinely used on SPHERE;3 (ii) cascaded ARMA models of order 2 identified using prediction error minimization (c-PEM) as proposed in.4, 5 Both s-AR2 and c-PEM were parameterized to produce tip or tilt state-space models up to order 20 and 30 respectively. We discuss the parallelized implementation in the real time computer and the expected performance. On-sky tests are scheduled during the November 2016 run or the January 2017 run.
Fighting vibrations on large telescopes is an arduous task. At Gemini, vibrations originating from cryogenic coolers have been shown to degrade the optical wavefront, in certain cases by as much as 40%. This paper discusses a general solution to vibration compensation by tracking the real time vibration state of the telescope and using M2 to apply corrections. Two approaches are then presented: an open loop compensation at M2 based on the signal of accelerometers at the M1 glass, and a closed loop compensation at M2 based on optical measurements from the wave front sensor. The paper elaborates on the pros and cons of each approach and the challenges faced during commissioning. A conclusion is presented with the final results of vibration tracking integrated with operations.
Non-common path aberrations (NCPA), in an adaptive optics system, are static aberrations induced by the science and wavefront sensor’s (WFS) separate light paths, for which the latter is corrected (although not present in the former), and the former is not. It was suspected1 that this type of aberration may significantly affect the image quality performance of Altair + NIRI, the Gemini North Observatory’s adaptive optics facility instrument and the near-infrared imaging camera. A simple and effective focal plane sharpening technique was developed to optimize these static aberrations for Altair & NIRI at f/32, and 2.12μm.
By varying the shape of the deformable mirror (DM) to introduce Zernike aberration coefficients through a reasonable range of values, the images produced were read out on the NIRI detector and analyzed for Strehl ratio. Fitting a second-order polynomial to this data set gave an optimized value for each coefficient out to Z49. The Strehl ratio was improved by 6% +/- 2% and the Z5 (45° astigmatism) term showed the only appreciable error contribution to the current NCPA offset of 0.15μm in k-prime (2.12μm). Aside from resulting in a slight improvement in image quality, the technique developed is non-invasive and will be implemented in other instruments and cameras that typically couple with Altair and have outdated or erroneous NCPA files currently. Furthermore, some high spatial-frequency structure in the PSF was found that limited the effect of these corrections, and may be a key component in further investigations towards image quality degradation in Altair + NIRI.
GeMS, the Gemini South MCAO System, has now been in operation for 3 years with the near infrared imager GSAOI. We first review the performance obtained by the system, the science cases and the current operational model. In the very near future, GeMS will undergo a profound metamorphosis, as we will integrate a new NGS wavefront sensor, replace the current 50W laser with a more robust one and prepare for a new operational model where operations will shift from the mountain to the base facility. Along this major evolution, we are also presenting several improvements on the loop control, calibrations and automatization of this complex system. We discuss here the progress of the different upgrades and what we expect in terms of performance improvements and operational efficiency.
NGS2 is an upgrade for the multi-natural guide star tip-tilt & plate scale wavefront sensor for GeMS (Gemini Multi-Conjugate Adaptive Optics system). It uses a single Nüvü HNü-512 Electron-Multiplied CCD array that spans the entire GeMS wavefront sensor focal plane. Multiple small regions-of-interest are used to enable frame rates up to 800Hz. This set up will improve the optical throughput with respect to the current wavefront sensor, as well as streamline acquisition and allow for distortion compensation.
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.
Altair is the facility single conjugate AO system for Gemini North. Although it has been in operation for more than 10 years (and upgraded to LGS in 2007), Altair's performance is degraded by three main issues: vibrations of the telescope and instrument support structure, spatial aliasing on centroid offsets from the M2 support structure print-through on the optical surface and static non-common path aberrations. Monte-Carlo simulations can reproduce the behavior of Altair when including these three effects and they are roughly of the same order of magnitude. Solutions or mitigations are being investigated to overcome these nefarious effects and restore Altair's performance to its nominal level. A simplex algorithm as well as a phase diversity approach are being investigated to measure and correct for static aberrations. A high accuracy phase map of the M2 print-through has been obtained and is being used to calibrate and/or filter centroids affected by aliasing. A new real time computer is under consideration, to be able to handle more advanced controllers, especially notch filters to combat vibrations. In this paper we will report on the various simulations and on-sky results of this rejuvenation of one of Gemini's workhorse instruments.
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.
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.
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 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.
The Gemini North (GN) AO system, Altair, has been routinely operating in LGS mode since 2007. Due to the initial
optical design, the NGS field-of-view (FoV) is limited to a radius ~ 25" which limits the potential science. To improve
this, we have tested the AO/LGS operation using a peripheral wavefront sensor (PWFS) whose patrol field is ~ 4'-7'
from the target. This expanded NGS FoV permits greater sky coverage but with decreased resolution, FWHM ~ 0.1" -
0.2" making this mode very suitable for non-imaging spectrographic and integral field unit observations. We present the
hardware and software upgrades to PWFS and Altair as well as the software necessary for making this observing mode a
routine and integral part of GN operations. Characterization and performance of this new operation mode, known as
LGS+P1, are presented.
We present observations of early-type galaxies with laser guide star adaptive optics (LGS AO) obtained at Gemini North
telescope using the NIFS integral field unit (IFU). We employ an innovative technique where the focus compensation
due to the changing distance to the sodium layer is made 'open loop', allowing the extended galaxy nucleus to be used
only for tip-tilt correction. The purpose of these observations is to determine high spatial resolution stellar kinematics
within the nuclei of these galaxies to determine the masses of the super-massive black holes. The resulting data have
spatial resolution of 0.2" FWHM or better. This is sufficient to positively constrain the presence of the central black hole
in even low-mass early-type galaxies, suggesting that larger samples of such objects could be observed with this
technique in the future. The open-loop focus correction technique is a supported queue-observing mode at Gemini,
significantly extending the sky coverage in particular for faint, extended guide sources. We also provide preliminary
results from tests combining tip/tilt correction from the Gemini peripheral guider with on-axis LGS. The current test
system demonstrates feasibility of this mode, providing about a factor 2-3 improvement over natural seeing. With
planned upgrades to the peripheral wave-front sensor, we hope to provide close to 100% sky coverage with low Strehl
corrections, or 'improved seeing', significantly increasing flux concentration for deep field and extended object studies.
We present up-to-date performance characteristics for natural guide star (NGS) operation of the ALTAIR adaptive optics
system at the Gemini N. 8m telescope. These results are obtained from a nightly performance monitoring campaign
where we obtain a consistent set of point spread functions (PSFs) over a broad range of observing conditions. These
results are compared with system modelling and circular buffer information from the Altair adaptive optics (AO) system.
The latter show residual tip-tilt errors with a median rms ~ 18.5 mas. We also present preliminary results from a new
operational mode of the laser guide star (LGS) AO which will eventually yield all-sky access with image FWHM ~ 0.1"