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Yayın The design of an adaptive optics telescope: the case of DAG(SPIE, 2016-07-27) Jolissaint, Laurent; Keskin, Onur; Zago, Lorenzo; Yerli, Sinan Kaan; Yeşilyaprak, Cahit; Mudry, Emeric; Lousberg, Grégory P.In this paper, we describe in detail the optical design of DAG, a new 4 m telescope for Turkey. DAG is an "adaptive optics friendly" telescope, in a sense that each design decision is taken considering the potential impact on the AO performance (vibrations, static aberrations etc.) The objective is to make this telescope fully ready for AO at first light. It is designed as a Ritchey-Chretien combination, 56 m focal length, with Nasmyth foci only, and active optics. Its total RMS error is expected to be 45 nm up to Zernike mode 78, and 26 nm for the higher, non AO corrected modes. A final design optimization has been done by the telescope manufacturers, demonstrating that our AO-based requirements can be satisfied, without much difficulty.Yayın DAG 4m telescope: assembly, integration and testing(SPIE-Int Soc Optical Engineering, 2018-07-06) Pirnay, Olivier; Lousberg, Grégory P.; Gabriel, Eric; Marchiori, Gianpietro; Busatta, Andrea; Yeşilyaprak, Cahit; Keskin, OnurAMOS with EIE as a main subcontractor, was awarded a contract in November 2014 for the design, manufacturing and installation of a 4m-class telescope for the Turkish Eastern Anatolia Observatory (DAG) situated at 3170 m above the sea level in Palandöken mountains. The telescope is based on a Ritchey-Chretien configuration with two folded Nasmyth focal planes and a focal length of 56m. Diffraction-limited performances will be reached thanks to the combination of the active optics system and the adaptive optics system that will be implemented on one of the Nasmyth ports. The active optics system aims at controlling the shape of the primary mirror by means of 66 axial force actuators and positioning actively the secondary and tertiary mirrors by means of hexapods. More than 30 years of experience in testing instruments and telescopes, including optical testing, alignment, metrology, mechanical static and dynamic measurements, system identification, etc. allow to implement an adequate verification strategy combining component level verifications with factory and site test in the most efficient and reliable manner. As a main contractor, AMOS is in charge of the overall project management, the system engineering, the optical design and the active optics development. As a main sub-contractor and partner of AMOS, EIE is in charge of the development of the mount. The factory test therefore takes place in EIE premises. In this paper is shortly presented the overall design of the telescope with a review of the specification, the optical design and a description of the major sub-systems, including the optics. The assembly, integration et test plan is outlined. The assembly sequence and the tests of the active optics and the mount are discussed. Finally, the site integration and tests are explained. The process to assess the image quality of the telescope and the verification instrument developed for this purpose by AMOS are presented.Yayın A flexible adaptive optics concept for general purpose high angular resolution science on the DAG 4m telescope(SPIE-Int Soc Optical Engineering, 2018) Jolissaint, Laurent; Bouxin, Audrey; Gökay, Ulaş Sabahattin; Keskin, Onur; Rigaut, Francois; Yeşilyaprak, CahitThanks to the availability of high actuator density deformable mirrors (ALPAO 468 DM), the high versatility of the pyramid wavefront sensor and above all, the venue of essentially no noise EMCCD detectors, it becomes possible to fully adapt the degree of correction of an adaptive optics system for a given guide star brightness and atmospheric condition. Indeed, when the conditions are very good, the high actuator density of the DM allows to reach a high Strehl by using all the modes, and when the conditions are less favorable, the spatial sampling, i. the number of modes, and the sensitivity of the detector allows to maximize the Strehl beyond what would be possible with a classical, frozen SH-WFS based system. Beside, oversampling the detector allows to relax the specification on the pupil images given by the pyramid on the detector, which in turn relaxes the pyramid prism manufacturing specifications. We are now designing an AO system for the DAG 4 m telescope that will allow, on the same system, ExAO as well as low order improved seeing observations. This article reports on the AO performance analysis, the final optical design and the design of the double prism achromatic pyramid.Yayın DAG 4m telescope: optics completion, on-site integration and test(SPIE, 2022) Pirnay, Olivier; Albart, Pierre; Bastin, Christian; De Ville, Jonathan; Gabriel, Eric; Leseur, Thibault; Lousberg, Grégory P.; Méant, Laurence; Orban, Sabrina; Tortolani, Jean-Marc; Amalfi, Manfredi; Marchiori, Gianpietro; Rampini, Francesco; Busatta, Andrea; Yeşilyaprak, Cahit; Keskin, OnurAMOS with EIE as main subcontractor has recently completed the erection of the 4 m telescope located at the Turkish Eastern Anatolia Observatory (DAG) set up by the Ataturk University Astrophysics Research and Application Centre (ATASAM) of Erzurum. The telescope design is based on a Ritchey-Chrétien configuration with two folded Nasmyth focal planes and a focal length of 56m. The optical train is composed of three mirrors: the primary mirror (M1) with an optical aperture of 4m, a convex secondary mirror (M2), and a large flat folding mirror (M3). Diffraction-limited performances in optical and near infrared spectral bands will be achieved thanks to the combination of active and adaptive optics systems. The active optics system is controlling the shape of the primary mirror by means of 66 axial force actuators and position actively the secondary and tertiary mirrors by means of hexapods. The adaptive optics system will be implemented at one of the two Nasmyth ports. As main contractor, AMOS is in charge of the overall project management, the system engineering, the optical design and the active optics development. As main sub-contractor and partner of AMOS, EIE is in charge of the development of the mount. Following the factory acceptance in Europe, the telescope was dismounted and delivered in early 2021. The activities onsite were carried out according to the assembly, integration and verification plan (AIV plan). In the meantime, the fabrication of the 4 m primary mirror was completed, and the full set of mirrors was forwarded on-site before the end of the year 2021. In this paper is presented a brief description of the design and performances of the telescope followed by the project progress status at the time the optics are being integrated in the telescope for the first time. This includes the review of the mirrors as-built quality and the excepted performances of the telescope mount after alignment and tuning. The path forward final acceptance is explained with the presentation of the optical alignment method and the test carried-out on-sky.Yayın TROIA Adaptive optics system for DAG telescope; assembly and laboratory performance prior to on-sky assessment(SPIE, 2022-08-29) Keskin, Onur; Jolissaint, Laurent; Bouxin, Audrey; Yeşilyaprak, CahitIn this article, we describe the current status of the development of TROIA* a pyramid wavefront sensor based adaptive optics system designed for DAG, a new 4 m telescope located in Eastern Anatolia, Turkey. The wavefront uses a no-noise electron-multiplied CCD camera, and the deformable mirror has a large actuators density, allowing coronagraphic science in one hand, but also system optimization for low light level or bad seeing conditions thanks to the versatility of the P-WFS. We describe the optical design, the mounting and alignment procedure and our loop control concept. Closed loop results are described, showing that while there are still many issues to fix before the sky version, the system behaves as expected.Yayın Auxiliary free space optical communication project to ensure continuous transfer of data for DAG the 4m telescope(SPIE, 2016) Keskin, Onur; Yeşilyaprak, Cahit; Yerli, Sinan KaanThe continuity of the amount of data that the 4m DAG (Eastern Anatolia Observatory in Turkish) telescope will produce and transfer to Ataturk University is critical not to jeopardize the science programs. Though the fiber optics and radio link infrastructures are in place, these systems are still volatile against earthquakes, and possible excavation damages. Thus the 4m DAG telescope will be equipped with a free space optical communication system to ensure the continuity of the data transfer as a backup system. In order to cope with the disturbances introduced by the atmospheric turbulence, the transceiver FSO system will be equipped with a wavefront corrector. In this paper, the Cassegrain optical design, and working principle of this system as well as expected performance analyses will be presented.Yayın Project management of DAG: Eastern Anatolia Observatory(SPIE, 2016) Keskin, Onur; Yeşilyaprak, Cahit; Yerli, Sinan Kaan; Zago, Lorenzo; Güver, Tolga; Aliş, SinanThe four meter DAG (Eastern Anatolia Observatory in Turkish) telescope is not only the largest telescope in Turkey but also the most promising telescope in the northern hemisphere with a large potential to offer scientific observations with its cutting edge technology. DAG is designed to be an AO telescope which will allow both infrared and visible observations with its two Nasmyth platforms dedicated to next generation focal plane instruments. In this paper, status updates from DAG telescope will be presented in terms of; (i) in house optical design of DAG, (ii) tender process of telescope, (iii) tender process of enclosure, and (iv) tender process of the observatory building. Also status updates from the focal plane instruments project and possible collaboration activities will be presented.Yayın Optical design of the adaptive optics system for DAG, the new 4 m Turkish telescope(SPIE, 2020) Bouxin, Audrey; Jolissaint, Laurent; Keskin, Onur; Yeşilyaprak, Cahit; Spanò, PaoloWe present the design of the Adaptive Optics System for the new Turkish 4-m telescope (DAG). The AO will use a pyramid WFS, with a double prism and a no noise EM-CCD camera to allow for oversampling of the pupil images and a relaxation of the prism manufacturing tolerances. In order to use the high modal resolution of the P-WFS allowed by the adjustment of the modulation angle, we implement a high order deformable mirror with 468 actuators, which will permit to use the system in extreme AO correction mode. The P-WFS optical design has been largely inspired by NFIRAOS truth WFS. The number of optical surfaces has been reduced to the bare minimum. An atmospheric dispersion compensator is introduced around the tip-tilt modulation mirror. In this proceeding, we present the detail of the optical design steps for all the components of the system.
