The Adaptive Optics (AO) of the Gran Telescopio Canarias (GTC) is a single conjugate postfocal system, integrated in one of the Nasmyth platforms of the telescope. GTC is located in the Observatory of Roque de Los Muchachos (ORM) in the island of La Palma, Spain. GTCAO is based on a single deformable mirror (DM) with 373 actuators, conjugated to the GTC pupil, and a Shack-Hartmann wavefront sensor (WFS) with 312 useful sub-apertures on an OCAM2 camera. The performance required for GTCAO is 65% Strehl Ratio in K-band under average atmospheric conditions and bright NGS. After finishing its laboratory testing and calibration in 2022, the laboratory acceptance and transport readiness review took place in April 2023. GTCAO integration in the telescope was carried out along June 2023. The GTCAO control software was integrated with the GTC observing software along July, to implement the optical derotation, the WFS positioning in the field and guiding, the WFS atmospheric dispersion compensation, and the tip-tilt correction loop implemented with the GTC secondary mirror. At the end of Summer 2023 started the on-sky commissioning. Since then, the AO loop has been closed on sky in different turbulence and guide star conditions. This paper presents the GTCAO integration results and first on sky commissioning results.
GTCAO is the instrument that implements Adaptive Optics on GTC. For atmospheric turbulence correction, GTCAO uses a deformable mirror. Unlike other AO systems, GTCAO does not include a dedicated mirror for low-frequency tip-tilt (TT) correction. In the absence of dedicated correction, the TT components of atmospheric turbulence are corrected by the deformable mirror (DM), using a significant portion of its working range and potentially leading to saturation. To mitigate this effect, GTCAO calculates low-frequency TT and offloads its correction to the telescope secondary mirror (M2) and primary axes. These actions optimize the use of the deformable mirror range for higher frequencies correction and extends the deformable mirror lifespan. This paper describes the approach implemented for calculating low-frequency TT from the information provided by the Shack-Hartmann wavefront sensor and the state of the DM, in both open-loop and closed-loop operation modes. Laboratory tests and telescope real observation results are also presented.
GRANCAIN (GRAN CAmara INfrarroja) is a first-light imaging instrument in the infrared J, H and K bands that will be integrated into the adaptive optics focus of the Gran Telescopio de Canarias. The purpose of the instrument is to capture SWIR diffraction-limited images for a field of view of 22x22 arcsec. The instrument boasts a telecentric optical design with a collimator-camera configuration featuring a 2:1 magnification ratio. Housed within a 160-liter aluminum cryostat, its optical path includes a cold stop, a filter wheel, and a 4Mpx Hawaii-2 PACE Teledyne detector, meticulously engineered for operation at 77K. The optics is held in place by black anodized 6061-T6 aluminum supports. These mounts serve the critical purpose of precisely positioning the optics along the Z optical axis. The opto-mechanical frames contain adjustment elements in five degrees of freedom (all except the clock) for optical alignment and to compensate the thermal differential contractions that occur during the cooling-down process. Additionally, the lens-housing cell combines different geometries and materials with different coefficients of thermal expansion to avoid stresses on the glass so as not vary its relative position. A symmetrical and athermalized opto-mechanical design, free of residual stresses, helps to minimize the deviations of the optical axis and thus facilitates the iterative process of optical alignment in cryogenic conditions. A strict manufacturing and metrological control process were necessary in order to achieve the objectives for optimum image quality. The article contains a detailed description of the design, fabrication techniques, metrology, integration, alignment, and testing of the athermalized opto-mechanical elements.
The RIZ & UBV visible spectrographs of the ANDES instrument, which are foreseen to be installed at the Extremely Large Telescope, require to be under a very stable high vacuum and at an extremely stable temperature of 1mK to reach the radial velocity goal of 10cm/s RMS over a 10-year period. The baseline design, integration and first analyses of the 5.5t aluminum vacuum tank, vacuum system, and the thermal enclosure of the two-room temperature spectrographs are presented in this paper. A very analogous configuration is proposed for both instruments in view of their similarities. In addition, this article addresses the finite rigidity of the Nasmyth platform and its consequences on the instrument design together with a potential collaborative multi-CAD Product Design Management platform description.
The first generation of ELT instruments includes an optical-infrared high resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs ([U]BV, RIZ, YJH) providing a spectral resolution of ∼100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 μm with the goal of extending it to 0.35-2.4 μm with the addition of an U arm to the BV spectrograph and a separate K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre-feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Modularity and fibre-feeding allows ANDES to be placed partly on the ELT Nasmyth platform and partly in the Coudé room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature’s fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of almost 300 scientists and engineers which include the majority of the scientific and technical expertise in the field that can be found in ESO member states.
We present the design of the ANDES UBV module, the bluest spectrograph of the ANDES instrument. It is a fiber-fed high resolution, high stability spectrograph, which will be installed on the ELT-Nasmyth platform to minimize blue fibre losses from the focal plane to the spectrograph. In this paper we present the status of development of the spectrograph, its optical design, and auxiliary devices like exposure meter and leveling system, at the preliminary design stage. As stability is the prime design driver, a thermal enclosure is provided to keep temperature of the optical train stable at ambient conditions, and the pressure is kept constant at high vacuum level. The science, sky background and simultaneous calibration light is fed to the spectrographs via fiber bundles of 66 fibres, which are arranged in a straight row forming the spectrograph slit.
The Gran Telescopio de Canarias Adaptive Optics System (GTCAO) is currently in its commissioning phase at Roque de Los Muchachos Observatory (ORM). The GTCAO is a single-conjugated post-focal system equipped with a Shack- Hartmann Wavefront Sensor (WFS) and a Deformable Mirror (DM) conjugated to the pupil, achieving a Strehl Ratio of 65% in the K-band by utilizing a natural bright star. By early 2023, the development of the AO system concluded at the facilities of the Instituto de Astrofísica de Canarias (IAC), where acceptance tests were carried out. Subsequently, the entire system was integrated onto the Nasmyth platform of the telescope, replicating the controlled laboratory conditions. During maritime and land transportation, the system was handled with the optics train integrated and high-precision alignment. This involved the development of specific transportation tools to prevent accelerations beyond 2g, which could induce plastic deformations and misalignments in the opto-mechanical components. Extensive vibration analysis and different Power Spectral Densities (PSD) profiles were crucial to meet the requirements. A rigorous integration procedure was devised to ensure safe assembly, spanning four consecutive daytime shifts. This meticulous approach was adopted to guarantee that the telescope’s observing hours remained uncompromised. This article provides a comprehensive account of the integration process and emphasizes the mechanical aspects. It includes static and dynamic mechanical analyses and technical details of handling, transport, and integration from the lab to the telescope to ensure safety and high precision assembly of opto-mechanical components.
We present here the preliminary design of the RIZ module, one of the visible spectrographs of the ANDES instrument. It is a fiber-fed high-resolution, high-stability spectrograph. Its design follows the guidelines of successful predecessors such as HARPS and ESPRESSO. In this paper we present the status of the spectrograph at the preliminary design stage. The spectrograph will be a warm, vacuum-operated, thermally controlled and fiber-fed echelle spectrograph. Following the phase A design, the huge etendue of the telescope will be reformed in the instrument with a long slit made of smaller fibers. We discuss the system design of the spectrographs system.
The Adaptive Optics system of the 10-m class Gran Telescopio Canarias (GTCAO) is completing the acceptance tests in the laboratory at the Instituto de Astrofísica de Canarias, to be ready for its integration in the telescope at Roque de Los Muchachos Observatory (ORM) in 2023. The AO system has been designed with robustness and operability as its key characteristics, and will be a facility of GTC. It features a single deformable mirror (DM) with 373 actuators, conjugated to the telescope pupil, and a Shack-Hartmann wavefront sensor (WFS) with 312 subapertures, using an OCAM2 camera. The expected performance of the GTCAO system working on average atmospheric conditions and bright NGS is 65% Strehl Ratio in K-band. In this paper we present the characterization of the system and the tests that have been performed for its acceptance at the laboratory. A series of calibrations are required and methodically run to achieve its ultimate performance: flatten the DM, acquire the Interaction Matrix and the reference slopes, correct the non-common path aberrations etc. The WFS requires additional calibrations, to compensate the pupil displacement in all the 2 arcminutes patrol field of view, and to correct the atmospheric dispersion in the visible. Close loop gains and sampling frequency are adapted to the changing conditions, and lookup tables are created for that purpose. The compliance with the system specifications has been verified. After verification of the final software functionalities for telescope operation, the system will be shipped to the ORM, to be installed and aligned on the Nasmyth platform of the GTC, and to be integrated with the telescope control system.
The Laser Guide Star Facility (LGSF) of Gran Telescopio Canarias (GTC) will be in charge of generating a Laser Guide Star (LGS) in the high atmosphere for the GTC Adaptive Optics System (GTCAO) to measure and correct the effect of the atmospheric turbulence. This proceeding analyses the thermal response of the LGS launch systems in operation under the direct action of the laser, and its interaction with respect GTC Telescope environment.
The Laser Guide Star Facility (LGSF) of GTC will generate a laser guide star (LGS) in the high atmosphere for the GTC Adaptive Optics System (GTCAO) to measure and correct the effect of the atmospheric turbulence. The GTCAO LGS Wavefront Sensor (LWS) will be based on a Shack Hartmann WFS and placed on the GTCAO optical bench, where the Natural Guide Star (NGS) Wavefront Sensor is already installed. The science dichroic splits the light beam so that the visible range (0.47-0.9μm) is reflected to the NGS WFS, and the infrared range 0.9-2.5μm is transmitted to the science instrument. A new second dichroic (LWS DC) will be installed in the visible path, to reflect 589nm (FWHM 12nm) towards the LWS, and to transmit the rest of the visible light to the NGS WFS. In addition, the system will count on an LGS calibration source. The proceeding describes the opto-mechanical design of the LWS System, covering its different subsystems: LWS Dichroic, LWS Sensor and LWS Calibration Unit.
The Natural Guide Star Adaptive Optics system for the Gran Telescopio Canarias (GTC) is in its integration phase, and meanwhile the Laser Guide Star update, which will follow two years later, has recently passed its Preliminary Design Phase. This LGS Facility will feature a TOPTICA Na laser, and it will open up the scientific possibilities of GTC enlarging the sky coverage of the AO system and allowing to study at high resolution more scientific targets. A trade-off study was undertaken to decide, among other details, the launching position of the laser and the feasibility of a further upgrade to an MCAO system vs technical complexity, cost and maintenance. As part of this study we have analysed the performance of the GTCAO LGS system to ensure that it will fulfil the specifications in all the different scenarios. Complete end-to-end (E2E) simulations have been performed using the versatile Durham AO Simulation Platform (DASP), including not only real atmospheric profiles from Observatorio del Roque de los Muchachos but also the measured windshake spectrum of the secondary mirror of GTC, the different control loops (TT, DM, focus), the laser uplink jitter and launching telescope divergence, the segmented primary mirror and it's cophasing residual errors, the rotating pupil etc... In this contribution we present a detailed error budget of the system and the results of the E2E simulations that show the impact that such a system will have on the science done with GTC.
The GTC AO system designed and developed during the last years is based on a single deformable mirror with 21 x 21 actuators, conjugated to the telescope pupil, and a Shack-Hartmann wavefront sensor with 20 x 20 subapertures, using an OCAM2 camera. The GTCAO system will provide a corrected beam with a Strehl Ratio (SR) of 0.65 in K-band with bright natural guide stars. This paper reports the updated status of the integration of GTCAO in the IAC laboratory, and the results obtained in the first tests carried out to evaluate the performance of the system, before the complete characterization and the verification of the requirements. The wavefront sensor verification has been completed, and it has been integrated in the optical bench together with the corrector optics including the CILAS deformable mirror. The calibration system, also mounted on the optical bench, includes light sources used to tune, characterise and calibrate the whole system. It also simulates the atmospheric turbulence and the telescope, delivering an aberrated wavefront used to debug the whole control system, and to test the real time control software, the servo loop and different servo control strategies. Finally the Test Camera has been also integrated at the science focus to evaluate the performance.
The Gran Telescopio Canarias Adaptive Optics (GTCAO) will measure the wavefront with a Shack-Hartmann sensor. This wavefront sensor (WFS) is based on the CCD220, an electron-multiplying CCD (EMCCD) that achieves sub-electron readout noise, increasing the signal to noise ratio when weak natural guide stars (NGS) are used as reference. GTCAO will start its operation in telescope with NGS, using only one wavefront sensor, and later it will incorporate a Laser Guide Star (LGS) and consequently a second WFS, also based on an EMCCD. Both EMCCDs and a third one used as spare, have been characterized and compared including the system gain, electron- multiplication gain, readout noise vs gain, excess noise and linearity. The EM gain calibration is important to keep all EMCCD channels in the linear regime and the camera manufacturer carries it out, but it is reported that the multiplication gain may suffer ageing and degradation even if the camera is not in use. This suggests the need to monitor this ageing. In this paper it is proposed and tested a procedure for predictive maintenance that re-characterize the system gain, electron- multiplication gain and linearity periodically in order to predict the eventual ageing of the EMCCD multiplying registers. This procedure can be carried out quickly while the detector is installed in the WFS and in operational status. In order to provide the required illumination, the GTCAO calibration system is used.
The Gran Telescopio Canarias Adaptive Optics (GTCAO) is a single-conjugated post-focal system with a Shack Hartmann wavefront sensor, and one Deformable Mirror (DM) conjugated to the pupil. The optical design for tip-tilt correction includes two different mirrors, DM and the telescope M2, being M2 also used for off-loading the DM to avoid reaching its stroke limits. This optical configuration is open to different control strategies that have been simulated with Matlab. Later it has also been simulated using Durham Adaptive optics Real-time Controller (DARC) and its AO simulator, DASP. Finally some preliminary laboratory results are presented.
The Gran Telescopio Canarias Adaptive Optics (GTCAO) is a single-conjugated post-focal system with a Shack Hartmann wavefront sensor working at visible wavelength and one Deformable Mirror (DM) conjugated to the pupil. GTCAO does not include a fast tip-tilt mirror in its optical bench so it relies on the telescope secondary mirror (M2) to correct low frequency tip-tilt and offload the DM. This paper describes specific details of the software implementation of the mirror control for GTCAO, analyses its computational needs, presents the series of tests performed on the newly designed AO closed loop, and summarises software optimizations and operating system configurations set in order to optimise computer performance in the available hardware architecture
This contribution is focused on the innovative aspects of the design of the Laser Guide Star (LGS) Facility for the Gran Telescopio Canarias (GTC) Adaptive Optics (GTCAO) System [6]. After a trade-off process considering different alternatives, a preliminary opto-mechanical design was defined, based on a “TOPTICA SodiumStar” laser to be launched on-axis. To maximize throughput, different novelties around the optical, and mechanical design of the Laser Launch System, including the Laser Head, the Beam Transfer Optics and the Launch Telescope are emphasized in this paper. In particular, all the elements of the Laser Launch System have been compacted to be placed at the backside envelope of the GTC M2 mechatronics. To fit in that envelope the thermal enclosure of the Laser Head had to be redefined to avoid mechanical interferences and science beam vignetting. An innovative closed-loop Laser Head cooling approach was defined to be also arranged at the backside of GTC M2. Performance simulations running in parallel to the on-axis LGS design could not determine any difference in performance between the on-axis and the off-axis launch. Hence, considering the higher packaging and maintenance complexity required by the on-axis launch, GTC decided to define the off-axis configuration as the new baseline approach. All the solutions already defined for the on-axis approach that were applicable to the new off-axis baseline were reused. To reduce the cost of future upgrades, the LGS design allows generating and launching several LGS with just one launch telescope splitting the light from the Laser Head. In parallel with keeping the volume of the facility to a minimum, an effort to keep its maintenance as simple as possible has been also made to avoid the impact on the telescope operational costs.
Robert Hammerschlag, Sander Deelen, Pieter Hoogendoorn, Johannes N. Kommers, Thomas Sonner, Roberto Simoes, Olivier Grassin, Andreas Fischer, Simon Visser, Kristof Thewissen
These open-foldable very light-weight domes, based on very strong textile membranes highly tensioned between steel bows, are designed for bad-weather protection and maintenance of instruments for astronomical, meteorological and civil-engineering measurements and have extremely high wind stability. The domes of the GREGOR telescope and the Dutch Open Telescope are the two existing prototypes. Improvements were developed with all parts light-colored to remain cool in solar light. The new specially made connection parts (eyes) between the textile parts are made from white-colored PETP, a very strong and UV-stable synthetic, and have a better geometrical shape giving higher stability. The rubber seal tubes on top of the dome were of black-colored chloride rubber CR (neoprene), strong and UV stable, but very warm in sunlight. New UV-stable EPDM rubber tubes were produced in natural light color. To get this rubber stiff enough to give good sealing, a black-colored stiff EPDM rubber is put inside the light-colored one. Tests were performed and the forces necessary for compression of the rubber tubes were measured. An inside black tube with a circa 1.3 times larger compression force than the original black tubes was applied. The assembling of the black tubes into the light-colored tubes was successfully applied at the DOT and GREGOR domes.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.