Paolo La Penna

The field stabilization and adaptive optics mirrors for the European Extremaly Large Telescope

A 42 meters telescope does require adaptive optics to provide few milli arcseconds resolution images. In the current design of the E-ELT, M4 provides adaptive correction while M5 is the field stabilization mirror. Both mirrors have an essential role in the E-ELT telescope strategy since they do not only correct for atmospheric turbulence but have also to cancel part of telescope wind shaking and static aberrations. Both mirrors specifications have been defined to avoid requesting over constrained requirements in term of stroke, speed and guide stars magnitude. Technical specifications and technological issues are discussed in this article. Critical aspects and roadmap to assess the feasibility of such mirrors are outlined.

ESO adaptive optics facility progress and first laboratory test results

The Adaptive Optics Facility project is completing the integration of its systems at ESO Headquarters in Garching. The main test bench ASSIST and the 2nd Generation M2-Unit (hosting the Deformable Secondary Mirror) have been granted acceptance late 2012. The DSM has undergone a series of tests on ASSIST in 2013 which have validated its optical performance and launched the System Test Phase of the AOF. This has been followed by the performance evaluation of the GRAAL natural guide star mode on-axis and will continue in 2014 with its Ground Layer AO mode. The GALACSI module (for MUSE) Wide-Field-Mode (GLAO) and the more challenging Narrow-Field-Mode (LTAO) will then be tested. The AOF has also taken delivery of the second scientific thin shell mirror and the first 22 Watt Sodium laser Unit. We will report on the system tests status, the performances evaluated on the ASSIST bench and advancement of the 4Laser Guide Star Facility. We will also present the near future plans for commissioning on the telescope and some considerations on tools to ensure an efficient operation of the Facility in Paranal.

Deploying the testbed for the VLT adaptive optics facility: ASSIST

The ESO Very Large Telescope Adaptive Optics Facility (VLT-AOF) will transform the VLT Unit Telescope 4 to an Adaptive Telescope. In absence of an intermediate focus before the Adaptive Secondary in this Ritchey–Chrétien type telescope and in order to reduce the testing and calibration of the system on-sky, ASSIST, The Adaptive Secondary Setup and Instrument STimulator, was developed. It provides an off-sky testing facility for the ESO AOF and will provide a full testing environment for three elements of the VLT Adaptive Optics Facility: the Deformable Secondary Mirror (DSM) and the AO modules for MUSE and HAWK-I (GALACSI and GRAAL). ASSIST was delivered to ESO Garching, where it was assembled and tested. Currently ASSIST is being integrated with the Deformable Secondary Mirror, the first step in the full system testing of the two AO systems for the VLT AOF on ASSIST. This paper briefly reviews the design and properties of ASSIST and reports on the first results of ASSIST in stand-alone mode.

ESO Adaptive Optics Facility Progress Report

The ESO Adaptive Optics Facility (AOF) consists in an evolution of one of the ESO VLT unit telescopes to a laser driven adaptive telescope with a deformable mirror in its optical train. The project has completed the procurement phase and several large structures have been delivered to Garching (Germany) and are being integrated (the AO modules GRAAL and GALACSI and the ASSIST test bench). The 4LGSF Laser (TOPTICA) has undergone final design review and a pre-production unit has been built and successfully tested. The Deformable Secondary Mirror is fully integrated and system tests have started with the first science grade thin shell mirror delivered by SAGEM. The integrated modules will be tested in stand-alone mode in 2012 and upon delivery of the DSM in late 2012, the system test phase will start. A commissioning strategy has been developed and will be updated before delivery to Paranal. A substantial effort has been spent in 2011-2012 to prepare the unit telescope to receive the AOF by preparing the mechanical interfaces and upgrading the cooling and electrical network. This preparation will also simplify the final installation of the facility on the telescope. A lot of attention is given to the system calibration, how to record and correct any misalignment and control the whole facility. A plan is being developed to efficiently operate the AOF after commissioning. This includes monitoring a relevant set of atmospheric parameters for scheduling and a Laser Traffic control system to assist the operator during the night and help/support the observing block preparation.

Alignment and integration of ASSIST: a test bench for VLT adaptive optics facility

ASSIST, The Adaptive Secondary Setup and Instrument STimulator, is being developed to provide a testing facility for the ESO Adaptive Optics Facility (AOF). It will allow the off-telescope testing of three elements of the VLT AOF; the Deformable Secondary Mirror (DSM) and the AO systems for MUSE and HAWK-I (GALACSI and GRAAL). The core of ASSIST consists of a 2-mirror setup (AM1-AM2) allowing the on-axis test of the DSM in interferometric mode. However, during the initial stages of ASSIST integration, DSM would not be present. This makes the task of aligning AM1-AM2 to within an accuracy of 0.05mm/1 arcmin rather challenging. A novel technique known as Shack-Hartmann method has been developed and tested in the lab for this purpose. A Shack Hartmann wavefront sensor will be used to measure the mis-alignment between AM1-AM2 by recording the coma and astigmatism in the presence of large spherical aberration introduced because of tilt/decenter of AM2 with respect to AM1. Thereafter, 20 optical components including lenses, flat mirrors and beam-splitter cubes divided into five sub-assemblies should be aligned to AM1-AM2- DSM axis which ultimately passes through the mechanical axis of large AMOS rotator.

Laboratory results of the AOF system testing

For two years starting in February 2014, the AO modules GRAAL for HAWK-I and GALACSI for MUSE of the Adaptive Optics Facility project have undergone System Testing at ESOs Headquarters. They offer four different modes: NGS SCAO, LGS GLAO in the IR, LGS GLAO and LTAO in the visible. A detailed characterization of those modes was made possible by the existence of ASSIST, a test bench emulating an adaptive VLT including the Deformable Secondary Mirror, a star simulator and turbulence generator and a VLT focal plane re-imager. This phase aimed at validating all the possible components and loops of the AO modules before installation at the actual VLT that comprises the added complexity of real LGSs, a harsher non-reproducible environment and the adaptive telescope control. In this paper we present some of the major results obtained and challenges encountered during the phase of System Tests, like the preparation of the Acquisition sequence, the testing of the Jitter loop, the performance optimization in GLAO and the offload of low-order modes from the DSM to the telescope (restricted to the M2 hexapod). The System Tests concluded with the successful acceptance, shipping, installation and first commissioning of GRAAL in 2015 as well as the acceptance and shipping of GALACSI, ready for installation and commissioning early 2017.

Adaptive Optics Facility: from an amazing present to a brilliant future...

The Adaptive Optics Facility (AOF) is an ESO project, which transformed Yepun, one of the four 8m telescopes in Paranal, into an adaptive telescope. This has been done by replacing the conventional secondary mirror of Yepun by a Deformable Secondary Mirror (DSM) and attaching four Laser Guide Stars (LGS) Units to its centerpiece. Additionally, two Adaptive Optics (AO) modules (GALACSI serving MUSE a 3D spectrograph, and GRAAL, serving Hawk I a wide field infrared imager) have been assembled onto the telescope Nasmyth adapters, each of them incorporating four LGS WaveFront Sensors (WFS) and one tip-tilt sensor used to control the DSM at 1 kHz frame rate. The complete AOF is installed on Yepun for more than one year now, and its commissioning is fully complete. This paper presents the most important and amazing features of the AOF, illustrated by some first science images obtained using MUSE/GALACSI in Ground Layer AO (GLAO) and Laser Tomography AO (LTAO) mode, and HAWK-I/GRAAL in GLAO mode. In the first part of the paper, on-sky performance of GRAAL and GALACSI is presented in terms of gain in image quality and even Strehl Ratio. Efficiency of the on-sky operation of the AOF is described. In the second part, future instruments making use of the AOF capabilities are presented.

Testing the VLT AO facility with ASSIST

The testing and verification of ESO Very Large Telescope Adaptive Optics Facility (VLT-AOF) requires new and innovative techniques to deal with the absence of an intermediate focus on the telescope. ASSIST, The Adaptive Secondary Setup and Instrument STimulator, was developed to provide a testing facility for the ESO AOF and will allow off-telescope testing of three elements of the VLT Adaptive Optics Facility; the Deformable Secondary Mirror (DSM) and the AO systems for MUSE and HAWK-I (GALACSI and GRAAL). ASSIST will provide a full testing environment which includes an interferometric testing mode for the DSM, an on-axis testing mode with a single wavefront sensor and full operation testing modes for both the AO systems. Both natural as well as laser guide stars will be simulated under various asterisms and a realistic turbulent atmosphere will be provided for varying atmospheric conditions. ASSIST passed its final design review and is now being manufactured, integrated and tested and will be operational in mid 2011, in time for first testing with the DSM.

Is ESO's adaptive optics facility suited for MCAO?

As of 2013, the ESOs VLT will be equipped with the Adaptive Optics Facility for Ground Layer and Laser Tomography adaptive optics assisted imaging and spectroscopy, using a Deformable Secondary Mirror and four Laser Guide Stars. Following the successful experience of the MAD demonstrator, we initiated a speculative study to evaluate the performance gain obtained by implementing a type of Multi-Conjugate Adaptive Optics correction that benefits from the unique features provided by the AOF. In this paper we present the basic concept and provide a first estimation of the correction performance obtained in the near infrared.

Control software for the AO modules of the AOF project

The Adaptive Optics Facility (AOF) is one of the most important ESO projects developed for the VLT programme in the last years. The AOF, currently still under commissioning, brings built-in AO capabilities (GLAO and LTAO) to one of the VLT 8m Telescopes (Yepun) that is now equipped with a deformable secondary mirror (DSM), four lasers guide stars (4LGSF) and two AO modules: GRAAL for the HAWK-I infrared imager and GALACSI for the MUSE 3D spectrograph. This paper describes the main aspects of the software responsible for the control and monitor of the two AO modules, as well as for the coordination of subsystems like the instruments and the telescope. Furthermore details of the strategy followed to minimize the impact on configuration control associated to several commissioning periods interleaved with normal operations will be given. The control software package consist of a set of modules based on the VLT Instrumentation Framework and on the VLT platform for AO Real-Time Applications (SPARTA). We will present the software and control design choices that have contributed to the successful commissioning and science verification of GALACSI Wide Field Mode (WFM) and the first verifications of GRAAL tip/tilt free mode covering the control of challenging devices such as the GRAAL Corotator or the GALACSI visible Field Selector together with the innovative and flexible implementation of the AO acquisition sequence and its seamless integration to the instrument observations, the handling of secondary loops and the development of health-check and commissioning scripts (templates) that automated the verification of the different observing modes.