The design of an adaptive optics telescope: the case of DAG

The optical design of the OWL 100-m class visible and near-infrared telescope, with integrated adaptive optics, departs substantially from classical two-mirror solutions. We propose using spherical shapes for the primary and secondary mirrors due to manufacturing, performance and cost constraints. The optical prescription must balance conflicting constraints such as the design of the telescope structure, the constraints set by adaptive tomography correction, and the feasibility of the corrective optics which compensates for the spherical and field aberrations of the primary-secondary mirrors. The number of mirrors, larger than in classical 2-mirror designs, implies additional variables. Within the limits set by the feasibility of optical testing of the aspheric surfaces, we present two optical designs for the telescope and derive high level requirements on active and adaptive control.

Ground-based and Airborne Telescopes V, 2014

The DAG (Turkish for Eastern Anatolia Observatory) 4-m telescope project has been formally launched in 2012, being fully funded by the Government of Turkey. This new observatory is to be located on a 3170 m altitude ridge near the town of Erzurum in Eastern Anatolia. First light is scheduled for late 2017. The DAG team's baseline design of the telescope consists of a Ritchey-Chretien type with alt-az mount, a focal length of 56 m and a field of view up to 30 arcmin. Multiple instruments will be located at the Nasmyth foci. The optical specifications of the telescope are set by DAG team for diffraction limited performance with active and adaptive optics. Modern mirror control technologies will allow defining in a most cost effective way the figuring requirements of the optical surfaces: the low order figuring errors of the combined optical train constituted of M1-M2-M3 are defined in terms of Zernike coefficients and referred to the M1 surface area. The high order figuring errors are defined using the phase structure functions. Daytime chilling of the closed enclosure volume and natural ventilation through suitable openings during observations will be used to ensure optimal mirror and dome seeing. A design of a ground layer adaptive optics (GLAO) subsystem is developed concurrently with the telescope. In this paper, main design aspects, the optical design and expected performance analysis of the telescope will be presented.

Proceedings of SPIE, 2006

In this paper, we provide an overview of the adaptive optics (AO) program for the Thirty Meter Telescope (TMT) project, including an update on requirements; the philosophical approach to developing an overall AO system architecture; the recently completed conceptual designs for facility and instrument AO systems; anticipated first light capabilities and upgrade options; and the hardware, software, and controls interfaces with the remainder of the observatory. Supporting work in AO component development, lab and field tests, and simulation and analysis is also discussed. Further detail on all of these subjects may be found in additional papers in this conference.

2006

The Adaptive Optics Facility is a project to convert UT4 into a specialised Adaptive Telescope. The present secondary mirror (M2) will be replaced by a new M2-Unit hosting a 1170-actuator deformable mirror. The three focal stations will be equipped with instruments adapted to the new capability of this UT. Two instruments have been identified for the two Nasmyth foci: Hawk-I with its AO module GRAAL allowing a Ground Layer Adaptive Optics correction and MUSE with GALACSI for GLAO correction and Laser Tomography Adaptive Optics correction. A future instrument still needs to be defined for the Cassegrain focus. Several guide stars are required for the type of adaptive corrections needed and a Four Laser Guide Star Facility (4LGSF) is being developed in the scope of the AO Facility. Convex mirrors like the VLT M2 represent a major challenge for testing and a substantial effort is dedicated to this. ASSIST, is a test bench that will allow testing of the Deformable Secondary Mirror and b...

Proceedings of the Adaptive Optics for Extremely Large Telescopes 5

The availability of small deformable mirrors with large number of actuators and stroke, on one hand, and versatile wavefront sensors (pyramid WFS), on the other, allows the development of AO systems whose equivalent pitch can be adapted freely to the guide stars and seeing conditions. On moderately large telescopes (4 m class) this flexibility allows a performance (Strehl and limiting magnitude) always better than what a classical, frozen Shack-Hartman design would allow. Moreover, adding several natural guide star wavefront sensors, we believe a single system could do anything from extreme AO to GLAO, i.e using the same hardware, and adapting the control software parameters to the observation mode. Taking advantage of such a system requires the use of a zoom optics in the imager in order to optimally match the plate scale with the PSF. We demonstrate that sub-optimal pixel size would result in a significant loss in term of science data reduction, in particular object detectability. The raison d'être of such a versatile system is to popularize AO in community of astronomers not familiar with it, by allowing, on the same telescope, high resolution as well as seeing improved observations. This is particularly important for countries where very few large telescopes are available. On the long term, we think that most moderate size telescopes will have this sort of flexible multipurpose AO systems as a default. The flexible AO concept will be implemented on the new 4 m Turkish telescope, DAG.

Proceedings of the International Astronomical Union, 2005

Adaptive Optics (AO) will be essential for accomplishing many, if not most, of the science objectives currently planned for Extremely Large Telescopes including GMT, OWL, and TMT. AO will be needed to support a range of instrumentation, including near infrared (IR) imagers and spectrometers, mid IR imagers and spectrometers, "planet finding" instrumentation and wide-field optical spectrographs. Multiple advanced AO systems, utilizing the full range of concepts currently under development, will need to be combined into an integrated architecture to meet a broad range of requirements for field-of-view, spatial resolution and spectral bandpass. In this paper, we describe several of the possible options for these systems and outline the range of issues, trade studies and component development activities which must be addressed. Some of these challenges include very high-order, large-stroke wavefront correction, tip-tilt sensing with faint natural guide stars to maximize sky coverage, laser guide star wavefront sensing on a very large aperture and achieving extremely high contrast ratios for the detection of extra-solar planet and other faint companions of nearby bright stars.

Journal of Astronomical Telescopes, Instruments, and Systems

Robo-AO is the first robotic autonomous laser-guided adaptive optics (AO) system operating in the sky. It is a very economical AO system especially suitable for observations with 1-to 3-m class telescopes. A second Robo-AO system, which works both in the visible and near-infrared wavelengths, has been developed to improve the image quality of the 2-m diameter telescope at Inter-university Centre for Astronomy and Astrophysics Girawali Observatory in India. We present the optomechanical design and development of the Laser Guide Star Facility (LGSF) and the Cassegrain AO facility with various test results. Effects of different projection geometries of the LGSF have been discussed with modeling results. Comprehensive study of an atmospheric dispersion corrector with dispersion model and development of a generic software are elaborated with experimental results. Toward the end, AO loop test results in the presence of artificial turbulence generated in the laboratory are presented.

Ground-based and Airborne Telescopes VI, 2016

Dogu Anatolu Gözlemevi (DAG-Eastern Anatolia Observatory) Project is a 4m class optical, near-infrared Telescope and suitable enclosure which will be located at an altitude of ~3.170m in Erzurum, Turkey. The DAG telescope is a project fully funded by Turkish Ministry of Development and the Atatürk University of Astrophysics Research Telescope-ATASAM. The Project is being developed by the Belgian company AMOS (project leader), which is also the optics supplier and EIE GROUP, the Telescope Main Structure supplier and responsible for the final site integration. The design of the Telescope Main Structure fits in the EIE TBO Program which aims at developing a Dome/Telescope systemic optimization process for both performances and competitive costs based on previous project commitments like NTT, VLT, VST and ASTRI. The optical Configuration of the DAG Telescope is a Ritchey-Chretien with two Nasmyth foci and a 4m primary thin mirror controlled in shape and position by an Active Optic System. The main characteristics of the Telescope Main Structure are an Altitude-Azimuth light and rigid structure system with Direct Drive Systems for both axis, AZ Hydrostatic Bearing System and Altitude standard bearing system; both axes are equipped with Tape Encoder System. An innovative Control System characterizes the telescope performance.

Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation II, 2016

An active optics system is being developed by AMOS for the new 4m-class telescope for the Turkish Eastern Anatolia Observatory (DAG). It consists in (a) an adjustable support for the primary mirror and (b) two hexapods supporting M2 and M3. The M1 axial support consists of 66 pneumatic actuators (for mirror shape corrections) associated with 9 hydraulic actuators that are arranged in three independent circuits so as to fix the axial position of the mirror. Both M1 support and the hexapods are actively controlled during regular telescope operations, either with look-up tables (openloop control) or using optical feedback from a wavefront sensor (closed-loop control).

Interferometry for Optical Astronomy II, 2003

In this paper we present results using a compact, portable adaptive optics system. The system was developed as a joint venture between the Naval Research Laboratory, Air Force Research Laboratory, and two small, New Mexico based-businesses. The system has a footprint of 18x24x18 inches and weighs less than 100 lbs. Key hardware design characteristics enable portability, easy mounting, and stable alignment. The system also enables quick calibration procedures, stable performance, and automatic adaptability to various pupil configurations. The system was tested during an engineering run in late July 2002 at the Naval Observatory Flagstaff Station one-meter telescope. Weather prevented extensive testing and the seeing during the run was marginal but a sufficient opportunity was provided for proof-of-concept, initial characterization of closed loop performance, and to start addressing some of the most pressing engineering and scientific issues.