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 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.
The QUIJOTE (Q-U-I joint Tenerife) experiment combines the operation of two radio-telescopes and three instruments working in the microwave bands 10–20 GHz, 26–36 GHz and 35–47 GHz at the Teide Observatory, Tenerife, and has already been presented in previous SPIE meetings (Hoyland, R. J. et al, 2012; Rubi˜no-Mart´ın et al., 2012). The Cosmology group at the IAC have designed a new upgrade to the MFI instrument in the band 10–20 GHz. The aim of the QUIJOTE telescopes is to characterise the polarised emission of the cosmic microwave background (CMB), as well as galactic and extra-galactic sources, at medium and large angular scales. This MFI2 will continue the survey at even higher sensitivity levels. The MFI2 project led by the Instituto de Astrof´ısica de Canarias (IAC) consists of five polarimeters, three of them operating in the sub-band 10–15 GHz, and two in the sub-band 15–20 GHz. The MFI2 instrument is expected to be a full two–three times more sensitive than the former MFI. The microwave complex correlator design has been replaced by a simple correlator design with a digital back-end based on the latest Xilinx FPGAs (ZCU111). During the first half of 2019 the manufacture of the new cryostat was completed and since then the opto-mechanical components have been designed and manufactured. It is expected that the cryogenic front-end will be completed by the end of 2022 along with the FPGA acquisition and observing system. This digital system has been employed to be more robust against stray ground-based and satellite interference, having a frequency resolution of 1 MHz
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 Gran Telescopio de Canarias Adaptive Optic System (GTCAO) is designed to provide nearly diffraction-limited images to GTC. GRANCAIN (GRAN CAmara INfrarroja) is a first light imaging instrument in J, H, and K infrared bands, and it will be integrated into the Nasmyth focus of GTCAO, contributing to carry out his acceptance tests. The instrument aims to capture NIR (Near-Infrared) diffraction limit images for a field of view of 22x22 arcsec operating up to seeing conditions of 1.5 arcsec and zenithal distances up to 60deg. The instrument has a telecentric optical design based on a collimator-camera with a 2:1 magnification, with a cold stop and the filters located in the collimated beam. The detector is a 4Mpx Hawaii-2 PACE Teledyne (H2P), which operates at 77K. The instrument is composed of a rectangular aluminum 6061-T6 cryostat cooled by a closed Gifford-McMahon helium cycle cryocooler with an optical bench where the entire optical train is mounted. The opto-mechanical system consists of two filter wheels, containing three wide and three narrowband filters in the J, H, and K bands in charge of selecting the wavelengths of the science images. Thanks to a wide background knowledge built up at the Instituto de Astrofísica de Canarias (IAC) and the use of commercial elements, the instrument development plan has been reduced to one year and a half. The article contains a general description of the design, fabrication, integration, and testing of the opto-mechanical elements, cryostat, cooling, and anti-vibration systems.
The Tenerife Microwave Spectrometer (TMS) is part of a renewed effort to study and characterize the CMB frequency distribution. The spectrometer is based on a pseudo-correlation architecture with two 10–20 GHz radiometer chains making use of both orthogonal linear polarizations, and will observe in this band with an angular and frequency resolutions of 3° and 1 MHz. The optical arrangement includes two corrugated feedhorns, one facing an internal calibrator to provide a cold reference signal, and the other pointing to the sky through the cryostat window by means of an offset-fed reflector. The optical system provides optimal cross-polarization properties (≤-30 dB) and symmetric beams, with minimum frequency dependence. The readout system is based on a SoC FPGA, providing fast data acquisition, high spectral resolution and stability. We present the current status of the TMS instrument, having described the scientific case of this instrument in the accompanying publication.
The Tenerife Microwave Spectrometer (TMS) is a new 10-20 GHz experiment that will be installed at the Teide Observatory (Tenerife, Spain), next to the QUIJOTE CMB experiment. The main TMS scientific driver is to accurately measure absolute distortions of the sky spectrum in the 10-20 GHz frequency range, with special emphasis on the characterization of the absolute synchrotron monopole from our Galaxy, and the possible deviations of the CMB spectrum from a pure blackbody law. TMS will provide an absolute calibration for the QUIJOTE experiment, and it will also serve as a prototype for future instruments of its type, both ground-based and satellites. Among its new instrumental design is an octave bandwidth high quality cryogenic front-end, a thermally stabilized cold black body and a new design of wide-band Fourier transform spectrometer. The spectrometer will have a resolution of 250 MHz, giving 40 spectrally stable sub-bands.
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.