SPIRou is an innovative near infra-red echelle spectropolarimeter and a high-precision velocimeter for the 3.6 m Canada-France-Hawaii Telescope (CFHT – Mauna Kea, Hawaii). This new generation instrument aims at detecting planetary worlds and Earth-like planets of nearby red dwarfs, in habitable zone, and studying the role of the stellar magnetic field during the process of low-mass stars / planets formation. The cryogenic spectrograph unit, cooled down at 80 K, is a fiber fed double-pass cross dispersed echelle spectrograph which works in the 0.98-2.40 μm wavelength range, allowing the coverage of the YJHK bands in a single exposure. Among the key parameters, a long-term thermal stability better than 2 mK, a relative radial velocity better than 1 m.s -1 and a spectral resolution of 70K are required. After ~ 1 year of assembly, integration and tests at IRAP/OMP (Toulouse, France) during 2016/2017, SPIRou was then shipped to Hawaii and completely re-integrated at CFHT during February 2018. A full instrument first light was performed on 24th of April 2018. The technical commissioning / science validation phase is in progress until June 2018, before opening to the science community. In this paper, we describe the work performed on integration and test of the opto-mechanical assemblies composing the spectrograph unit, firstly in-lab, in Toulouse and then on site, at CFHT. A review of the performances obtained in-lab (in 2017) and during the first on-sky results (in 2018) is also presented.
Since 1st light in 2002, HARPS has been setting the standard in the exo-planet detection by radial velocity (RV) measurements. Based on this experience, our consortium is developing a high accuracy near-infrared RV spectrograph covering YJH bands to detect and characterize low-mass planets in the habitable zone of M dwarfs. It will allow RV measurements at the 1-m/s level and will look for habitable planets around M- type stars by following up the candidates found by the upcoming space missions TESS, CHEOPS and later PLATO. NIRPS and HARPS, working simultaneously on the ESO 3.6m are bound to become a single powerful high-resolution, high-fidelity spectrograph covering from 0.4 to 1.8 micron. NIRPS will complement HARPS in validating earth-like planets found around G and K-type stars whose signal is at the same order of magnitude than the stellar noise. Because at equal resolving power the overall dimensions of a spectrograph vary linearly with the input beam étendue, spectrograph designed for seeing-limited observations are large and expensive. NIRPS will use a high order adaptive optics system to couple the starlight into a fiber corresponding to 0.4” on the sky as efficiently or better than HARPS or ESPRESSO couple the light 0.9” fiber. This allows the spectrograph to be very compact, more thermally stable and less costly. Using a custom tan(θ)=4 dispersion grating in combination with a start-of-the-art Hawaii4RG detector makes NIRPS very efficient with complete coverage of the YJH bands at 110’000 resolution. NIRPS works in a regime that is in-between the usual multi-mode (MM) where 1000’s of modes propagates in the fiber and the single mode well suited for perfect optical systems. This regime called few-modes regime is prone to modal noise- Results from a significant R and D effort made to characterize and circumvent the modal noise show that this contribution to the performance budget shall not preclude the RV performance to be achieved.
The Gemini Planet Imager (GPI) is a facility extreme-AO high-contrast instrument – optimized solely for study of faint companions – on the Gemini telescope. It combines a high-order MEMS AO system (1493 active actuators), an apodized pupil Lyot coronagraph, a high-accuracy IR post-coronagraph wavefront sensor, and a near-infrared integral field spectrograph. GPI incorporates several other novel features such as ultra-high quality optics, a spatially-filtered wavefront sensor, and new calibration techniques. GPI had first light in November 2013. This paper presnets results of first-light and performance verification and optimization and shows early science results including extrasolar planet spectra and polarimetric detection of the HR4696A disk. GPI is now achieving contrasts approaching 10-6 at 0.5” in 30 minute exposures.
The Gemini Planet Imager (GPI) entered on-sky commissioning and had its first-light at the Gemini South (GS) telescope in November 2013. GPI is an extreme adaptive optics (XAO), high-contrast imager and integral-field spectrograph dedicated to the direct detection of hot exo-planets down to a Jupiter mass. The performance of the apodized pupil Lyot coronagraph depends critically upon the residual wavefront error (design goal of 60nmRMS with <5 mas RMS tip/tilt), and therefore is most sensitive to vibration (internal or external) of Gemini's instrument suite. Excess vibration can be mitigated by a variety of methods such as passive or active dampening at the instrument or telescope structure or Kalman filtering of specific frequencies with the AO control loop. Understanding the sources, magnitudes and impact of vibration is key to mitigation. This paper gives an overview of related investigations based on instrument data (GPI AO module) as well as external data from accelerometer sensors placed at different locations on the GS telescope structure. We report the status of related mitigation efforts, and present corresponding results.
The Gemini Planet Imager is an extreme AO instrument with an integral field spectrograph (IFS) operating in Y, J, H, and K bands. Both the Gemini telescope and the GPI instrument are very complex systems. Our goal is that the combined telescope and instrument system may be run by one observer operating the instrument, and one operator controlling the telescope and the acquisition of light to the instrument. This requires a smooth integration between the two systems and easily operated control interfaces. We discuss the definition of the software and hardware interfaces, their implementation and testing, and the integration of the instrument with the telescope environment.
We present the results of both laboratory and on sky astrometric characterization of the Gemini Planet Imager (GPI). This characterization includes measurement of the pixel scale* of the integral field spectrograph (IFS), the position of the
detector with respect to north, and optical distortion. Two of these three quantities (pixel scale and distortion) were
measured in the laboratory using two transparent grids of spots, one with a square pattern and the other with a random pattern. The pixel scale in the laboratory was also estimate using small movements of the artificial star unit (ASU) in the
GPI adaptive optics system. On sky, the pixel scale and the north angle are determined using a number of known binary or multiple systems and Solar System objects, a subsample of which had concurrent measurements at Keck Observatory. Our current estimate of the GPI pixel scale is 14.14 ± 0.01 millarcseconds/pixel, and the north angle is -1.00 ± 0.03°. Distortion is shown to be small, with an average positional residual of 0.26 pixels over the field of view, and is corrected using a 5th order polynomial. We also present results from Monte Carlo simulations of the GPI Exoplanet Survey (GPIES) assuming GPI achieves ~1 milliarcsecond relative astrometric precision. We find that with this precision, we
will be able to constrain the eccentricities of all detected planets, and possibly determine the underlying eccentricity
distribution of widely separated Jovians.
The first light instrument on the Thirty Meter Telescope (TMT) project will be the InfraRed Imaging Spectrograph
(IRIS). IRIS will be mounted on a bottom port of the facility AO instrument NFIRAOS. IRIS will report guiding
information to the NFIRAOS through the On-Instrument Wavefront Sensor (OIWFS) that is part of IRIS. This will be in
a self-contained compartment of IRIS and will provide three deployable wavefront sensor probe arms. This entire unit
will be rotated to provide field de-rotation. Currently in our preliminary design stage our efforts have included:
prototyping of the probe arm to determine the accuracy of this critical component, handling cart design and reviewing
different types of glass for the atmospheric dispersion.
The Gemini Planet Imager (GPI) is an “extreme” adaptive optics coronagraph system that is now on the
Gemini South telescope in Chile. This instrument is composed of three different systems that historically have
been separate instruments. These systems are the extreme Adaptive Optics system, with deformable mirrors,
including a high-order 64x64 element MEMS system; the Science Instrument, which is a near-infrared
integral field spectrograph; and the Calibration system, a precision IR wavefront sensor that also holds
key coronagraph components. Each system coordinates actions that require precise timing. The
observatory is responsible for starting these actions and has typically done this asynchronously across
independent systems. Despite this complexity we strived to provide an interface that is as close to a onebutton
approach as possible. This paper will describe the sequencing of these systems both internally and
externally through the observatory.
An Atmospheric Dispersion Corrector (ADC) uses a double-prism arrangement to nullify the vertical chromatic
dispersion introduced by the atmosphere at non-zero zenith distances.
The ADC installed in the Gemini Planet Imager (GPI) was first tested in August 2012 while the instrument was
in the laboratory. GPI was installed at the Gemini South telescope in August 2013 and first light occurred later
that year on November 11th.
In this paper, we give an overview of the characterizations and performance of this ADC unit obtained in the
laboratory and on sky, as well as the structure of its control software.
The Gemini Planet Imager (GPI) is a complex optical system designed to directly detect the self-emission of young
planets within two arcseconds of their host stars. After suppressing the starlight with an advanced AO system and
apodized coronagraph, the dominant residual contamination in the focal plane are speckles from the atmosphere and
optical surfaces. Since speckles are diffractive in nature their positions in the field are strongly wavelength dependent,
while an actual companion planet will remain at fixed separation. By comparing multiple images at different
wavelengths taken simultaneously, we can freeze the speckle pattern and extract the planet light adding an order of
magnitude of contrast. To achieve a bandpass of 20%, sufficient to perform speckle suppression, and to observe the
entire two arcsecond field of view at diffraction limited sampling, we designed and built an integral field spectrograph
with extremely low wavefront error and almost no chromatic aberration. The spectrograph is fully cryogenic and
operates in the wavelength range 1 to 2.4 microns with five selectable filters. A prism is used to produce a spectral
resolution of 45 in the primary detection band and maintain high throughput. Based on the OSIRIS spectrograph at
Keck, we selected to use a lenslet-based spectrograph to achieve an rms wavefront error of approximately 25 nm. Over
36,000 spectra are taken simultaneously and reassembled into image cubes that have roughly 192x192 spatial elements
and contain between 11 and 20 spectral channels. The primary dispersion prism can be replaced with a Wollaston prism
for dual polarization measurements. The spectrograph also has a pupil-viewing mode for alignment and calibration.
SPIRou is a near-IR echelle spectropolarimeter and high-precision velocimeter under construction as a next-
generation instrument for the Canada-France-Hawaii-Telescope. It is designed to cover a very wide simultaneous
near-IR spectral range (0.98-2.35 μm) at a resolving power of 73.5K, providing unpolarized and polarized
spectra of low-mass stars at a radial velocity (RV) precision of 1m/s. The main science goals of SPIRou are
the detection of habitable super-Earths around low-mass stars and the study of stellar magnetism of star at
the early stages of their formation. Following a successful final design review in Spring 2014, SPIRou is now
under construction and is scheduled to see first light in late 2017. We present an overview of key aspects of
SPIRou’s optical and mechanical design.
SPIRou is a near-infrared, echelle spectropolarimeter/velocimeter under design for the 3.6m Canada-France-Hawaii
Telescope (CFHT) on Mauna Kea, Hawaii. The unique scientific capabilities and technical design features are described
in the accompanying (eight) papers at this conference. In this paper we focus on the lens design of the optical
spectrograph. The SPIROU spectrograph is a near infrared fiber fed double pass cross dispersed spectrograph. The
cryogenic spectrograph is connected with the Cassegrain unit by the two science fibers. It is also fed by the fiber coming
from the calibration box and RV reference module of the instrument. It includes 2 off-axis parabolas (1 in double pass),
an echelle grating, a train of cross disperser prisms (in double pass), a flat folding mirror, a refractive camera and a
detector. This paper describes the optical design of the spectrograph unit and estimates the performances. In particular,
the echelle grating options are discussed as the goal grating is not available from the market.
We present performance results, from in-lab testing, of the Integral Field Spectrograph (IFS) for the Gemini Planet Imager (GPI). GPI is a facility class instrument for the Gemini Observatory with the primary goal of directly detecting young Jovian planets. The GPI IFS is based on concepts from the OSIRIS instrument at Keck and utilizes an infrared transmissive lenslet array to sample a rectangular 2.8 x 2.8 arcsecond field of view. The IFS provides low-resolution spectra across five bands between 1 and 2.5μm. Alternatively, the dispersing element can be replaced with a Wollaston prism to provide broadband polarimetry across the same five filter bands. The IFS construction was based at the University of California, Los Angeles in collaboration with the Université de Montr eal, Immervision and Lawrence Livermore National Laboratory. During its construction, we encountered an unusual noise source from microphonic pickup by the Hawaii-2RG detector. We describe this noise and how we eliminated it through vibration isolation. The IFS has passed its preship review and was shipped to University of California, Santa Cruz at the end of 2011 for integration with the remaining sub-systems of GPI. The IFS has been integrated with the rest of GPI and is delivering high quality spectral datacubes of GPI's coronagraphic field.
This paper presents an overview of the PDR level mechanical and opto-mechanical design of the cryogenic spectrograph
unit of the nIR spectropolarimeter (SPIROU) proposed as a new-generation instrument for CFHT. The design is driven
by the need for high thermo-mechanical stability in terms of the radial velocity (RV) of 1 m/s during one night, with the
requirement for thermal stability set at 1 mK/24 hours. This paper describes stress-free design of the cryogenic optical
mounts, mechanical design of the custom-build cryostat, mechanical design of the optical bench, and thermal design for
1 mK thermal stability. The thermal budget was calculated using lumped-mass model thermal analysis, implemented in
Modelica multi-domain modeling language. Discussion of thermal control options to achieve 1 mK thermal stability is
The Gemini Planet Imager is a next-generation instrument for the direct detection and characterization of young warm exoplanets, designed to be an order of magnitude more sensitive than existing facilities. It combines a 1700-actuator adaptive optics system, an apodized-pupil Lyot coronagraph, a precision interferometric infrared wavefront sensor, and a integral field spectrograph. All hardware and software subsystems are now complete and undergoing integration and test at UC Santa Cruz. We will present test results on each subsystem and the results of end-to-end testing. In laboratory testing, GPI has achieved a raw contrast (without post-processing) of 10-6 5σ at 0.4”, and with multiwavelength speckle suppression, 2x10-7 at the same separation.
SPIRou is a near-IR (0.98-2.35μm), echelle spectropolarimeter / high precision velocimeter being designed as a next-generation instrument for the 3.6m Canada-France-Hawaii Telescope on Mauna Kea, Hawaii, with the main goal of
detecting Earth-like planets around low mass stars and magnetic fields of forming stars. The unique scientific and
technical capabilities of SPIRou are described in a series of seven companion papers. In this paper, the fiber links which
connects the polarimeter unit to the cryogenic spectrograph unit (35 meter apart) are described. The pupil slicer which
forms a slit compatible with the spectrograph entrance specifications is also discussed in this paper.
Some challenging aspects are presented. In particular this paper will focus on the manufacturing of 35 meter fibers with a
very low loss attenuation (< 13dB/km) in the non-usual fiber spectral domain from 0.98 μm to 2.35 μm. Other aspects as
the scrambling performance of the fiber links to reach high accuracy radial velocity measurements (1m/s) and the design
of the pupil slicer exposed at a cryogenic and vacuum environment will be discussed.
SPIRou is a near-infrared, echelle spectropolarimeter/velocimeter under design for the 3.6m Canada-France-
Hawaii Telescope (CFHT) on Mauna Kea, Hawaii. The unique scientific capabilities and technical design features
are described in the accompanying papers at this conference. In this paper we focus on the data reduction software
(DRS) and the data simulation tool. The SPIRou DRS builds upon the experience of the existing SOPHIE,
HARPS and ESPADONS spectrographs; class-leaders instruments for high-precision RV measurements and
spectropolarimetry. While SPIRou shares many characteristics with these instruments, moving to the near-
infrared domain brings specific data-processing challenges: the presence of a large number of telluric absorption
lines, strong emission sky lines, thermal background, science arrays with poorer cosmetics, etc. In order for the
DRS to be fully functional for SPIRou's first light in 2015, we developed a data simulation tool that incorporates
numerous instrumental and observational e_ects. We present an overview of the DRS and the simulation tool
Small deformable mirrors (DMs) produced using microelectromechanical systems (MEMS) techniques have been used
in thermally stable, bench-top laboratory environments. With advances in MEMS DM technology, a variety of field
applications are becoming more common, such as the Gemini Planet Imager’s (GPI) adaptive optics system.
Instruments at the Gemini Observatory operate in conditions where fluctuating ambient temperature, varying gravity
orientations and humidity and dust can have a significant effect on DM performance. As such, it is crucial that the
mechanical design of the MEMS DM mount be tailored to the environment. GPI’s approach has been to mount a 4096
actuator MEMS DM, developed by Boston Micromachines Corporation, using high performance optical mounting
techniques rather than a typical laboratory set-up. Flexures are incorporated into the DM mount to reduce deformations
on the optical surface due to thermal fluctuations. These flexures have also been sized to maintain alignment under
varying gravity vector orientations. This paper is a follow-up to a previous paper which presented the preliminary
design. The completed design of the opto-mechanical mounting scheme is discussed and results from finite element
analysis are presented, including predicting the stability of the mirror surface in varying gravity vectors and thermal
Exoplanet imaging is driving a race to higher contrast imaging, both from earth and from space. Next-generation
instruments such as the Gemini Planet Imager (GPI) and SPHERE are designed to achieve contrast ratios of
10-6 - 10-7 this requires very good wavefront correction and coronagraphic control of diffraction. GPI is a
facility instrument, now in integration and test, with first light on the 8-m Gemini South telescope expected
by the middle of 2012. It combines a 1700 subaperture AO system using a MEMS deformable mirror, an
apodized-pupil Lyot coronagraph, a high-accuracy IR interferometric wavefront calibration system, and a nearinfrared
integral field spectrograph to allow detection and characterization of self-luminous extrasolar planets
at planet/star contrast ratios of 10-7. In this paper we will discuss the status of the integration and test now
taking place at the University of Santa Cruz California.
The Gemini Planet Imager (GPI), currently under construction for the 8-m Gemini South telescope, is a high contrast adaptive
optics instrument intended for direct imaging of extrasolar planets and circumstellar disks. GPI will study circumstellar
disks using the polarization of disk-scattered starlight. These observations will be obtained using a novel 'integral field
polarimetry' mode, in which the dispersing prism of GPI's integral field spectrograph is replaced by a Wollaston prism,
providing simultaneous dual polarimetry for each position in the field of view. By splitting polarizations only after the instrument's
lenslet array, this design minimizes wavefront differences between the polarization channels, providing optimal
contrast for circumstellar dust. A rotating achromatic waveplate provides modulation. End-to-end numerical modeling
indicates that GPI will be sensitive to scattered light from debris disks significantly fainter than can currently be imaged.
We discuss the tradeoffs and design decisions for GPI polarimetry, describe the calibration and reduction procedures, and
present the current status of the instrument. First light is planned for 2011.
The Gemini Planet Imager (GPI) is an extreme AO coronagraphic integral field unit YJHK spectrograph destined
for first light on the 8m Gemini South telescope in 2011. GPI fields a 1500 channel AO system feeding an
apodized pupil Lyot coronagraph, and a nIR non-common-path slow wavefront sensor. It targets detection and
characterizion of relatively young (<2GYr), self luminous planets up to 10 million times as faint as their primary
star. We present the coronagraph subsystem's in-lab performance, and describe the studies required to specify
and fabricate the coronagraph. Coronagraphic pupil apodization is implemented with metallic half-tone screens
on glass, and the focal plane occulters are deep reactive ion etched holes in optically polished silicon mirrors. Our
JH testbed achieves H-band contrast below a million at separations above 5 resolution elements, without using
an AO system. We present an overview of the coronagraphic masks and our testbed coronagraphic data. We
also demonstrate the performance of an astrometric and photometric grid that enables coronagraphic astrometry
relative to the primary star in every exposure, a proven technique that has yielded on-sky precision of the order
of a milliarsecond.
The Gemini Planet Imager (GPI) is a new facility instrument to be commissioned at the 8-m Gemini South
telescope in early 2011. It combines of several subsystems including a 1500 subaperture Extreme Adaptive
Optics system, an Apodized Pupil Lyot Coronagraph, a near-infrared high-accuracy interferometric wavefront
sensor, and an Integral Field Unit Spectrograph, which serves as the science instrument. GPI's main scientific
goal is to detect and characterize relatively young (<2GYr), self luminous planets with planet-star brightness
ratios of ≤ 10-7 in the near infrared. Here we present an overview of the coronagraph subsystem, which includes
a pupil apodization, a hard-edged focal plane mask and a Lyot stop. We discuss designs optimization, masks
fabrication and testing. We describe a near infrared testbed, which achieved broadband contrast (H-band)
below 10-6 at separations > 5λ/D, without active wavefront control (no deformable mirror). We use Fresnel
propagation modeling to analyze the testbed results.
The Gemini Planet Imager (GPI) is a facility instrument under construction for the 8-m Gemini South telescope. It
combines a 1500 subaperture AO system using a MEMS deformable mirror, an apodized-pupil Lyot coronagraph, a
high-accuracy IR interferometer calibration system, and a near-infrared integral field spectrograph to allow detection and
characterization of self-luminous extrasolar planets at planet/star contrast ratios of 10-7. I will discuss the evolution from
science requirements through modeling to the final detailed design, provide an overview of the subsystems and show
models of the instrument's predicted performance.
Although many of the instruments planned for the TMT (Thirty Meter Telescope) have their own closely-coupled adaptive
optics systems, TMT will also have a facility Adaptive Optics (AO) system, NFIRAOS, feeding three instruments
on the Nasmyth platform. This Narrow-Field Infrared Adaptive Optics System, employs conventional deformable mirrors
with large diameters of about 300 mm. The requirements for NFIRAOS include 1.0-2.5 microns wavelength range,
30 arcsecond diameter science field of view (FOV), excellent sky coverage, and diffraction-limited atmospheric turbulence
compensation (specified at 133 nm RMS including residual telescope and science instrument errors.) The reference
design for NFIRAOS includes six sodium laser guide stars over a 70 arcsecond FOV, and multiple infrared tip/tilt sensors
and a natural guide star focus sensor within instruments. Larger telescopes require greater deformable mirror (DM)
stroke. Although initially NFIRAOS will correct a 10 arcsecond science field, it uses two deformable mirrors in series,
partly to provide sufficient stroke for atmospheric correction over the 30 m telescope aperture, but mainly to improve
sky coverage by sharpening near-IR natural guide stars over a 2 arcminute diameter "technical" field. The planned upgrade
to full performance includes replacing the ground-conjugated DM with a higher actuator density, and using a deformable
telescope secondary mirror as a "woofer." NFIRAOS feeds three live instruments: a near-Infrared integral field
Imaging spectrograph, a near-infrared echelle spectrograph, and after upgrading NFIRAOS to full multi-conjugation, a
wide field (30 arcsecond) infrared camera.
The next major frontier in the study of extrasolar planets is direct imaging detection of the planets themselves. With high-order adaptive optics, careful system design, and advanced coronagraphy, it is possible for an AO system on a 8-m class telescope to achieve contrast levels of 10-7 to 10-8, sufficient to detect warm self-luminous Jovian planets in the solar neighborhood. Such direct detection is sensitive to planets inaccessible to current radial-velocity surveys and allows spectral characterization of the planets, shedding light on planet formation and the structure of other solar systems. We have begun the construction of such a system for the Gemini Observatory. Dubbed the Gemini Planet Imager (GPI), this instrument should be deployed in 2010 on the Gemini South telescope. It combines a 2000-actuator MEMS-based AO system, an apodized-pupil Lyot coronagraph, a precision infrared interferometer for real-time wavefront calibration at the nanometer level, and a infrared integral field spectrograph for detection and characterization of the target planets. GPI will be able to achieve Strehl ratios > 0.9 at 1.65 microns and to observe a broad sample of science targets with I band magnitudes less than 8. In addition to planet detection, GPI will also be capable of polarimetric imaging of circumstellar dust disks, studies of evolved stars, and high-Strehl imaging spectroscopy of bright targets. We present here an overview of the GPI instrument design, an error budget highlighting key technological challenges, and models of the system performance.
Although many of the instruments planned for the TMT (Thirty Meter Telescope) have their own closely-coupled adaptive optics systems, TMT will also have a facility Adaptive Optics (AO) system feeding three instruments on the Nasmyth platform. For this Narrow-Field Infrared Adaptive Optics System, NFIRAOS (pronounced nefarious), the TMT project considered two architectures. One, described in this paper, employs conventional deformable mirrors with large diameters of about 300 mm and this is the reference design adopted by the TMT project. An alternative design based on MEMS was also studied, and is being presented separately in this conference. The requirements for NFIRAOS include 0.8-5 microns wavelength range, 30 arcsecond diameter output field of view (FOV), excellent sky coverage, and diffraction-
limited atmospheric turbulence compensation (specified at 133 nm RMS including residual telescope and science instrument errors.) The reference design for NFIRAOS includes multiple sodium laser guide stars over a 70 arcsecond FOV, and an infrared tip/tilt/focus/astigmatism natural guide star sensor within instruments. Larger telescopes require greater deformable mirror (DM) stroke. Although initially NFIRAOS will correct a 10 arcsecond science field, it uses two deformable mirrors in series, partly to provide sufficient stroke for atmospheric correction over the 30 m telescope aperture, but mainly to partially correct a 2 arcminute diameter "technical" field to sharpen near-IR natural guide stars and improve sky coverage. The planned upgrade to full performance includes replacing the groundconjugated DM with a higher actuator density, and using a deformable telescope secondary mirror as a "woofer." NFIRAOS incorporates an instrument rotator and selection of three live instruments: a near-Infrared integral field Imaging
spectrograph, a near-infrared echelle spectrograph, and after upgrading NFIRAOS to full multi-conjugation, a wide field (30 arcsecond) infrared camera.
The Gemini North adaptive optics system Altair utilises five cooperative CPU's to perform all the associated real-time tasks. One, the reconstructor (RTC), manages all of the highest speed hard real-time duties. As well as the core, computationally intensive, wavefront reconstruction, this processor implements a number of algorithms providing control system support services. These include: the quad-cell centroid gain estimation, determination and subtraction of invisible modes on the deformable mirror, and the blending of tip, tilt and focus from the on instrument wavefront sensors (which exist on all facility Gemini instruments).
These associated support tasks are critically important to ensure that the system always runs with an optimal bandwidth and produce stable images with no artefacts such as a waffle pattern or residual non-common path errors. We present the original algorithm that we have developed for the centroid gain estimate and discuss how it is efficiently and conveniently implemented on the hard real-time processor.
A wide-field low-resolution multi-object optical spectrograph suitable for a 30-m F/15 telescope is described. The effort to build a 30-m class telescope is gaining momentum. Many science cases for such a telescope make the need for a wide-field seeing-limited spectrograph a high priority. Our concept comprises four identical instruments placed symmetrically around the optical axis of the telescope, this allows smaller dimensions for the spectrographs and their components. Each instrument is placed in one quadrant of the telescope focal plane; a space at the center of the field is free for other instrumentation. Using a dichroic beam-splitter each instrument feeds a "red" and "blue" camera. The total field is 81 square arcmin, the wavelength range covers simultaneously 310 nm to 1000 nm and the spectral resolution (R) is 300 to 5000. The instruments are designed for vertical mounting at a Nasmyth focus to avoid gravity vector changes and reducing mechanical flexure problems during observation. The layout also allows access to internal components for maintenance. The design offers advantages for the location of a slit mask and filters. The instruments can also be used for imaging. Optical and opto-mechanical models and analyses are presented with specifications and expected performance.
The reflective coatings applied to telescope mirrors affect not only the optical performance, but also affect significantly the telescope operation. Replacement of a primary segment of a large segmented mirror is expected to be a major event. An increased service life span of such segment is of enormous value. The optics community is currently aggressively pursuing development in broadband high reflective durable coatings. We are undertaking research with the goal of a high, broadband reflective coatings that, with appropriate cleaning and in situ maintenance, will provide a service life time of more than seven years. Based on the VLOT (Very Large Optical Telescope) project requirements, we conducted a literature search on available materials, thin film deposition and cleaning processes to get as much information as possible. The results of this survey will be presented as the starting point of our study. Different thin film processes have been identified but energetic processes such as Reactive Low Voltage Ion Plating (RLVIP), Magnetron Sputtering and Ion Beam Assisted Deposition (IBAD) will be of great interest for durable coating fabrication. Regarding the cleaning process, we have concentrated our effort on laser cleaning processes.
We describe the VLOT integrated model, which simulates the telescope optical performance under the influence of external disturbances including wind. Details of the implementation in the MATLAB/SIMULINK environment are given, and the data structures are described. The structural to optical interface is detailed, including a discussion of coordinate transformations. The optical model includes both an interface with ZEMAX to perform raytracing analysis and an efficient Linear Optics Model for producing telescope optical path differences from within MATLAB. An extensive set of optical analysis routines has been developed for use with the integrated model. The telescope finite element model, state-space formulation and the high fidelity 1500 mode modal state-space structural dynamics model are presented. Control systems and wind models are described. We present preliminary results, showing the delivered image quality under the influence of wind on the primary mirror, with and without primary mirror control.
Canada has pursued conceptual design work and technical studies related to a 20-m segmented mirror telescope (VLOT). This paper provides an overview of the Canadian effort over the last 3 years. VLOT can achieve exciting and significant scientific goals that are not possible with today's 8-meter class telescopes. The scientific promise of instruments on a 20-m telescope enhanced by adaptive optics is particularly exciting. The technical work done thus far indicates that while there are many challenges in designing and constructing a VLOT and its instruments, a 20-m telescope is feasible and achievable without major advances in technology.
Proc. SPIE. 4839, Adaptive Optical System Technologies II
KEYWORDS: Actuators, Curium, Real-time computing, Control systems design, Adaptive optics, Gemini Observatory, Signal processing, Data processing, Matrix multiplication, Commercial off the shelf technology
Many reconstructors, or Real Time Controllers (RTC), for mono-conjugate AO systems are currently operating with many more about to be commissioned. The advent of faster and more efficient CPUs has permitted this task to be accomplished on a single processing element, for all but the highest order systems.
However, the demands on the RTC increase by an order of magnitude or so in the case of a Multi-Conjugate AO (MCAO) system. Multiple Wavefront Sensors (WFS) and multiple deformable mirrors increase the complexity, processing load and data flow rates that the RTC must deal with. No currently available single processing unit is capable of meeting this demand and retain the advantages of a cost-effective, flexible system. Multiple processing units must be employed.
We present in this paper a general architecture that addresses these issues. We present an analysis of the requirements of the Gemini South MCAO system on the RTC. This is followed by an algorithmic decomposition that simplifies the problem, lending itself to the use of commercially available multi-CPU single board computers. This is supported by the results of benchmark tests aimed at verifying the capabilities of one sample SBC. We conclude by presenting a description of the extendability of this architectural approach in the face of yet higher demands such as more mirrors, WFSs or complexity.
Altair is the AO system developed by the National Research Council of Canada for the Gemini North Telescope. Currently in the integration phase, the performance of the system, and in particular, of the real-time controller (RTC), is being fully characterised.
We begin with a review of the requirements for the RTC, the context within the rest of the Wavefront Control System, and a description of the processing the RTC is responsible for. We then present the actual performance results of the RTC integrated within Altair. We compare these with the benchmarked results.
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 Observatory is planning to implement a Multi Conjugate Adaptive Optics System as a facility instrument for the Gemini-South telescope. The system will include 5 Laser Guide Stars, 3 Natural Guide Stars, and 3 Deformable mirrors optically conjugated at different altitudes to achieve near-uniform atmospheric compensation over a 1 arc minute square field of view. The control of such a system will be split in 3 main functions: the control of the opto- mechanical assemblies of the whole system (including the Laser, the Beam Transfer Optics and the Adaptive Optics bench), the control of the Adaptive Optics System itself at a rate of 800 frames per second and the control of the safety system. The control of the adaptive Optics System is the most critical in terms of real time performance. In this paper, we will describe the requirements for the whole Multi Conjugate Adaptive Optica Control System, preliminary designs for the control of the opto-mechanical devices and architecture options for the control of the Adaptive Optics system and the safety system.
Altair is the facility Adaptive Optics (AO) system for the Gemini North Telescope on Mauna Kea, Hawaii. Designed to take advantage of the excellent natural seeing conditions that Gemini North will experience, Altair is also unique in that the Deformable Mirror (DM) is conjugate to a fixed altitude of 6.5 kilometers. Running at a control loop speed of at least one kHz, the reconstructor for this high order AO system is subject to a number of conditions that drove its design and implementation. Initial studies indicated that a single RISC CPU would be capable of performing the reconstruction for Altair, as opposed to the more common solution of multiple DSP processors. We present some of these conditions, the results of a throughput benchmark test that verified the choice of hardware, some components of the processing steps of the reconstructor and a summary of the current status of the project.
The Gemini Adaptive Optics System, (Altair), under construction at the National Research Council of Canada's Herzberg Institute of Astrophysics is unique among AO systems. Altair is designed with its deformable mirror (DM) conjugate to high altitude. We summarize construction progress. We then describe Altair in more detail. Both the Wavefront sensor foreoptics and control system are unconventional, because the guide star footprint on an altitude-conjugated DM moves as the guide star position varies. During a typical nodding sequence, where the telescope moves 10 arcseconds between exposures, this footprint moves by half an actuator and/or WFS lenslet. The advantages of altitude conjugation include increased isoplanatic patch size, which improves sky coverage, and improved uniformity of the corrected field. Altitude conjugation also reduces focal anisoplanatism with laser beacons. Although the initial installation of Altair will use natural guide stars, it will be fully ready to use a laser guide star (LGS). The infrastructure of Gemini observatory provides a variety of wavefront sensors and nested control loops that together permit some unique design concepts for Altair.
The Gemini Telescopes Project is a collaboration to develop two leading edge 8 meter telescopes; Gemini North on Mauna Kea, Hawaii, and Gemini South at Cerro Pachon, Chile. These telescopes will exploit the excellent natural image quality that these telescopes will provide, a natural guide star (NGS) adaptive optics (AO) system is being developed for Gemini North.
The Gemini Adaptive Optics System, under construction at the Dominium Astrophysical Observatory of the National Research Council of Canada's Herzberg Institute of Astrophysics is unique among AO systems. Altair is designed with its deformable mirror (DM) conjugate to high altitude. This concept is only practical at an observatory where extraordinary measures have been taken to reduce local seeing degradation. We summarize these measures. We then describe Altair. Both the wavefront sensor foreoptics and control system are unconventional, because the guide star footprint on an altitude-conjugated DM moves as the guide star position varies. During a typical nodding sequence, where the telescope moves 10 arcseconds between exposures, this footprint moves by half an actuator and/or WFS lenslet. The advantages of altitude conjugation include increased isoplanatic patch size, which improves sky coverage, and improved uniformity of the corrected field. Although the initial installation of Altair will use natural guide stars, it will include features to use a laser guide star with minimal rework. Altitude conjugation also reduces focal anisoplanatism with laser beacons. The infrastructure of Gemini observatory provides a variety of wavefront sensor and nested control loops that together permit some unique design concepts of Altair.
Each of the two Gemini telescopes will be instrumented with the Gemini Multi-Object Spectrograph (GMOS), a general purpose optical spectrograph mounted at one of the Cassegrain foci. Two GMOS are currently being designed and built by a team of scientists and engineers in Canada and in the UK. A stringent flexure specification is imposed on these instruments by the scientific requirement to measure velocity to high precision, 2 km/s at R equals 5,000 with 0.5 arcsec slits. This implies a basic stability specification of 3.125 micrometer/hour at the detector focal plane. The GMOS design has met this specification by using a combination of stiff structure (where flexure is minimized); Serrurier trusses (where the flexure is controlled); precision mechanisms (where mechanical hysteresis and error are minimized) and, finally, an open-loop active correction system at the detector focal plane (where the CCD is translated to counteract any residual flexure). Once the GMOS design was conceptualized and its component groups were identified, the design team divided the basic stability specification into allowable contribution from each group. The final division was weighted according to the degree of design difficulty, based on inputs from the engineers. An error budget was developed and maintained to ensure that GMOS would meet its overall flexure specification by controlling the contribution from each component. The error budget approach will be described and discussed in the paper. We will also look at examples from the GMOS design with reference to calculations, analyses, FEA and actual measurements from prototype components.
As the only two optical instruments appearing in its first fleet of instrumentation, the GEMINI MultiObject Spectrograph (GMOS) are indeed being developed as workhorse instruments. One GMOS will be located at each of the GEMINI telescopes to perform: (1) exquisite direct imaging, (2) 5.5 arcminute longslit spectroscopy, (3) up to 600 object multislit spectroscopy, and (4) about 2000 element integral field spectroscopy. The GMOSs are the only GEMINI instrumentation duplicated at both telescopes. The UK and Canadian GMOS team successfully completed their critical design review in February 1997. They are now well into the fabrication phase, and will soon approach integration of the first instrument. The first GMOS is scheduled to be delivered to Mauna Kea in the fall of '99 and the second to Cerro Pachon one year later. In this paper, we will look at how a few of the more interesting details of the final GMOS design help meet its demanding scientific requirements. These include its transmissive optical design and mask handling mechanisms. We will also discuss our plans for the mask handling process in GEMINI's queue scheduled environment, from the taking of direct images through to the use of masks on the telescope. Finally, we present the status of fabrication and integration work to date.
Improvements to the general dome conditions and the use of near IR detectors at the National Research Council of Canada's 1.8m Plaskett Telescope have stressed the abilities of the existing encoders. An encoding system that could be installed without telescope downtime and with a minimal impact on resources was necessary. These, and other, issues motivated the development of a method of non-contact encoding using a long line-scan CCD, a precision insensitive ruled tape and digital imaging metrology. Based on previously published simulation and experimental result a project to install such a system on the polar axis of the Plaskett Telescope was initiated. In this paper we present the overall design strategy, processing algorithms and initial test result and analysis. We end with recommendations to improve the capabilities of the approach.
The two Gemini multiple object spectrographs (GMOS) are being designed and built for use with the Gemini telescopes on Mauna Kea and Cerro Pachon starting in 1999 and 2000 respectively. They have four operating modes: imaging, long slit spectroscopy, aperture plate multiple object spectroscopy and area (or integral field) spectroscopy. The spectrograph uses refracting optics for both the collimator and camera and uses grating dispersion. The image quality delivered to the spectrograph is anticipated to be excellent and the design is driven by the need to retain this acuity over a large wavelength range and the full 5.5 arcminute field of view. The spectrograph optics are required to perform from 0.36 to 1.8 microns although it is likely that the northern and southern versions of GMOS will use coatings optimized for the red and blue respectively. A stringent flexure specification is imposed by the scientific requirement to measure velocities to high precision (1 - 2 km/s). Here we present an overview of the design concentrating on the optical and mechanical aspects.
The fabrication requirements of the Gemini multi-object spectrograph (GMOS) slit mask is discussed particularly in terms of the slit-to-slit position, slit geometry and the telescope operation. The demand for precision slit masks with high quality slits of width of less than quarter arcsecond and an allowable fabrication time of two hours required examination of innovative fabrication processes and mask materials. Different fabrication processes including high precision cutting processes, water-jet and laser machining systems are evaluated according to cost, speed and efficiency, and the findings are documented. Different candidate mask materials including low thermal expansion metals and novel materials such as graphite paper and carbon-fiber composite sheet, are evaluated according to their relevant mechanical and physical properties, and the findings are also documented. In addition to identifying that the most suitable mask material is unidirectional carbon fiber sheet and the corresponding fabrication process is a Nd:YAG laser machining system, the mask handling system for GMOS is described and methodology to minimize systematic fabrication errors is also proposed.
Encoding the angular position of large telescopes is typically achieved through the use of friction driven rotary encoders, tape style encoders mounted on the circumference of each telescope axis or co-axially mounted high precision rotary encoders. These forms of encoding have very stringent mounting requirements, are expensive, adversely affected by contaminating particles and often difficult to retrofit to existing telescopes. The advent of long CCDs presents the opportunity to develop accurate position encoding for telescope control using digital image metrology. In this paper we present the design of a high precision non- contact encoding system which uses the detection of multiple redundant visual edge features to develop sub-pixel edge position measurements to a precision of 1/50th pixel. The method is described in detail and is validated with both simulation trials and experimental results from a testbed setup.
Infrared (IR) observations have traditionally been limited to a relatively small number of specialized telescopes since: (1) the cost of detectors and detector system development is large; and (2) there are a number of significant technical differences associated with an 'infrared-capable' telescope when compared to a traditional optical telescope. With the advent of lower cost infrared detectors in recent years, IR instrumentation now becomes accessible to observatories with budgets unable to support the traditional high costs. We have assembled a complete observing system making use of a Hughes 256 X 256 pixel PtSi 1 - 5 micron array detector. This particular PtSi detector was chosen because it has several characteristics conducive to precise photometric observations. The detector has 100% fill factor, a large dynamic range of 104, low dark current and the potential for extremely good stability. The system we describe was designed with an emphasis on simplicity and the use of commercially available hardware and software, while retaining full performance of the detector. The system proved to integrate easily into the CCD observing environment used on our telescopes.