The new deployable tertiary mirror for the Keck I telescope (K1DM3) at the W. M. Keck Observatory has been assembled, tested and shipped to the telescope site, and is currently being installed. The mirror is capable of reflecting the beam to one of six positions around the telescope elevation ring or to retract out of the way to allow the use of Cassegrain instruments. This new functionality is intended to allow rapid instrument changes for transient event observations and improve telescope operations. This paper presents the final as-built design. Additionally, this paper presents detailed information about our alignment approach in the attempt to duplicate the instrument pointing orientation of the existing M3.
We present progress in efforts underway at the University of California Observatories to develop high performance durable silver-based mirror coatings for telescope and instruments. Silver-based coatings are extremely prone to tarnish and/or corrosion, and successful coatings depend not only on the materials used but also the deposition processes employed. Our physical vapor deposition (PVD) chamber allows both sputtering and ion-assisted e-beam depositions for head-to-head comparison of deposition processes, and we present results of these comparisons. In this paper, we review the problem and discuss our recent activities and findings. We discuss a systematic study to determine which oxides, nitrides and fluorides provide the best protection in environmental tests. We present initial results into the effects of stress in our specific thin films, and thee effects of stress on mirror coating durability. We also discuss studies using Atomic Layer Deposition (ALD) over-coating of Ag, and we describe a large ALD research chamber currently under construction that will demonstrate ALD processes on larger substrates (70 cm diameter).
Motivated by the ever increasing pursuit of science with the transient sky (dubbed Time Domain Astronomy or TDA), we are fabricating and will commission a new deployable tertiary mirror for the Keck I telescope (K1DM3) at the W.M. Keck Observatory. This paper presents the detailed design of K1DM3 with emphasis on the opto- mechanics. This project has presented several design challenges. Foremost are the competing requirements to avoid vignetting the light path when retracted against a sufficiently rigid system for high-precision and repeatable pointing. The design utilizes an actuated swing arm to retract the mirror or deploy it into a kinematic coupling. The K1DM3 project has also required the design and development of custom connections to provide power, communications, and compressed air to the system. This NSF-MRI funded project is planned to be commissioned in Spring 2017.
The Lick Observatory's Shane 3-meter telescope has been upgraded with a new infrared instrument (ShARCS - Shane Adaptive optics infraRed Camera and Spectrograph) and dual-deformable mirror adaptive optics (AO) system (ShaneAO). We present first-light measurements of imaging sensitivity in the Ks band. We compare mea- sured results to predicted signal-to-noise ratio and magnitude limits from modeling the emissivity and throughput of ShaneAO and ShARCS. The model was validated by comparing its results to the Keck telescope adaptive optics system model and then by estimating the sky background and limiting magnitudes for IRCAL, the pre- vious infra-red detector on the Shane telescope, and comparing to measured, published results. We predict that the ShaneAO system will measure lower sky backgrounds and achieve 20% higher throughput across the JHK bands despite having more optical surfaces than the current system. It will enable imaging of fainter objects (by 1-2 magnitudes) and will be faster to reach a fiducial signal-to-noise ratio by a factor of 10-13. We highlight the improvements in performance over the previous AO system and its camera, IRCAL.
The University of California Observatories will design and construct a deployable tertiary mirror (named K1DM3) for the Keck 1 telescope, which will complement technical and scientific advances in the area of time-domain astronomy. The K1DM3 device will enable astronomers to swap between any of the foci on Keck 1 in under 2 minutes, both to monitor varying sources (e.g. stars orbiting the Galactic center) and catch rapidly fading sources (e.g. supernovae, flares, gamma-ray bursts). In this paper, we report on the design development during our in-progress Preliminary Design phase. The design consists of a passive wiffle tree axial support system and a diaphragm lateral support system with a 5 arcminute field-of-view mirror. The mirror assembly is inserted into the light path with an actuation system and it relies on a kinematic mechanism for achieving repeatable, precise positioning. This project, funded by an NSF MRI grant, aspires to complete by the end of 2016.
A new high-order adaptive optics system is now being commissioned at the Lick Observatory Shane 3-meter telescope in California. This system uses a high return efficiency sodium beacon and a combination of low and high-order deformable mirrors to achieve diffraction-limited imaging over a wide spectrum of infrared science wavelengths covering 0.8 to 2.2 microns. We present the design performance goals and the first on-sky test results. We discuss several innovations that make this system a pathfinder for next generation AO systems. These include a unique woofer-tweeter control that provides full dynamic range correction from tip/tilt to 16 cycles, variable pupil sampling wavefront sensor, new enhanced silver coatings developed at UC Observatories that improve science and LGS throughput, and tight mechanical rigidity that enables a multi-hour diffraction-limited exposure in LGS mode for faint object spectroscopy science.
A Cassegrain mounted adaptive optics instrument presents unique challenges for opto-mechanical design. The flexure and temperature tolerances for stability are tighter than those of seeing limited instruments. This criteria requires particular attention to material properties and mounting techniques. This paper addresses the mechanical designs developed to meet the optical functional requirements. One of the key considerations was to have gravitational deformations, which vary with telescope orientation, stay within the optical error budget, or ensure that we can compensate with a steering mirror by maintaining predictable elastic behavior. Here we look at several cases where deformation is predicted with finite element analysis and Hertzian deformation analysis and also tested. Techniques used to address thermal deformation compensation without the use of low CTE materials will also be discussed.
We describe progress in the on-going effort at the University of California Observatories Advanced Coatings Lab to
develop efficient, durable silver-based coatings for telescope mirrors. We have continued to improve previously
identified recipes produced with e-beam ion-assisted deposition (IAD). We have started exploring nitride adhesion and
barrier layers added to or replacing layers in promising recipes. Our coating chamber now has one magnetron installed,
and two more will be added shortly so we can perform direct comparisons of e-beam IAD and sputtering processes for
the same recipes. We report on recent tests and findings relevant to protected-Ag coatings, including e-beam vs sputter
deposited silver; our current work with nitrides; and a comparison of certain fluorides. While focused on telescope
mirror coatings, we have also developed and tested two Ag-based coatings suitable for AO and for CCD-range
instruments. We also report on field-testing of earlier samples that have been exposed in the dome of the 3-m telescope
at Lick Observatory for a period of 2 years. Finally, we describe results of a pilot study using atomic-layer deposition
(ALD), a chemical vapor deposition technique, to produce barrier layers over silver. Optical quality ALD films are
smooth, conformal and have excellent uniformity and thickness control, and their barrier properties look extremely
promising for protecting silver from corrosion.
The Lick Observatory 3-meter telescope has a history of serving as a testbed for innovative adaptive optics techniques.
In 1996, it became one of the first astronomical observatories to employ laser guide star (LGS) adaptive optics as a
facility instrument available to the astronomy community. Work on a second-generation LGS adaptive optics system,
ShaneAO, is well underway, with plans to deploy on telescope in 2013. In this paper we discuss key design features and
implementation plans for the ShaneAO adaptive optics system. Once again, the Shane 3-m will host a number of new
techniques and technologies vital to the development of future adaptive optics systems on larger telescopes. Included is a
woofer-tweeter based wavefront correction system incorporating a voice-coil actuated, low spatial and temporal
bandwidth, high stroke deformable mirror in conjunction with a high order, high bandwidth MEMs deformable mirror.
The existing dye laser, in operation since 1996, will be replaced with a fiber laser recently developed at Lawrence
Livermore National Laboratories. The system will also incorporate a high-sensitivity, high bandwidth wavefront sensor
camera. Enhanced IR performance will be achieved by replacing the existing PICNIC infrared array with an Hawaii
2RG. The updated ShaneAO system will provide opportunities to test predictive control algorithms for adaptive optics.
Capabilities for astronomical spectroscopy, polarimetry, and visible-light adaptive optical astronomy will be supported.