This PDF file contains the front matter associated with SPIE Proceedings Volume 9151 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

The Cherenkov Telescope Array (CTA) project aims to create the next generation Very High Energy (VHE) gamma-ray telescope array. It will be devoted to the observation of gamma rays over a wide band of energy, from a few tens of GeV to more than 100 TeV. Two sites are foreseen to view the whole sky where about 100 telescopes, composed of three different classes, related to the specific energy region to be investigated, will be installed. Among these, the Small Size class of Telescopes, SSTs, are devoted to the highest energy region, to beyond 100 TeV. Due to the large number of SSTs, their unit cost is an important parameter. At the Observatoire de Paris, we have designed a prototype of a Small Size Telescope named SST-GATE, based on the dual-mirror Schwarzschild-Couder optical formula, which has never before been implemented in the design of a telescope. Over the last two years, we developed a mechanical design for SST-GATE from the optical and preliminary mechanical designs made by the University of Durham. The integration of this telescope is currently in progress. Since the early stages of mechanical design of SST-GATE, finite element method has been used employing shape and topology optimization techniques to help design several elements of the telescope. This allowed optimization of the mechanical stiffness/mass ratio, leading to a lightweight and less expensive mechanical structure. These techniques and the resulting mechanical design are detailed in this paper. We will also describe the finite element analyses carried out to calculate the mechanical deformations and the stresses in the structure under observing and survival conditions.

ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) SST-2M is an end-to-end prototype of Small Size class of Telescope for the Cherenkov Telescope Array. It will apply a dual mirror configuration to Imaging Atmospheric Cherenkov Telescopes. The 18 segments composing the primary mirror (diameter 4.3 m) are equipped with an active optics system enabling optical re-alignment during telescope slew. The secondary mirror (diameter 1.8 m) can be moved along three degrees of freedom to perform focus and tilt corrections. We describe the kinematic model used to predict the system performance as well as the hardware and software design solution that will be implemented for optics control.

Deformable mirrors can be used in cryogenic instruments to compensate for temperature-induced deformations. A unimorph-type deformable mirror consists of a mirror substrate and a piezoelectric layer bonded on substrates rear surface. A challenge in the design of the deformable mirror is the lack of knowledge about material properties. Therefore, we measured the coefficient of thermal expansion (CTE) of the substrate material TiAl6V4 between 295 K and 86 K. The manufactured mirror is characterized by an adaptive optical measurement setup in front of a test cryostat. The measured mirror deformations are feedback into a finite element model to calculate the CTE of the piezoelectric layer. We compare our obtained results to other published CTE-values for the piezoelectric material PIC151.

A novel active mirror concept based on carbon fiber reinforced polymer (CFRP) materials is presented. A nanolaminate facesheet, active piezoelectric layer and printed electronics are implemented in order to provide the reflective surface, actuation capabilities and electrical wiring for the mirror. Mirrors of this design are extremely thin (500-850 µm), lightweight (~ 2 kg/m²) and have large actuation capabilities (~ 100 µm peak- to-valley deformation per channel). Replication techniques along with simple bonding/transferring processes are implemented eliminating the need for grinding and polishing steps. An outline of the overall design, component materials and fabrication processes is presented. A method to size the active layer for a given mirror design, along with simulation predictions on the correction capabilities of the mirror are also outlined. A custom metrology system used to capture the highly deformable nature of the mirrors is demonstrated along with preliminary prototype measurements.

An approach for the online co-phasing of segmented telescopes using dual wavelength digital holography has been proposed. In this approach, two digital interferograms, one fringe pattern for one wavelength, which are acquired by a high speed CCD camera using a Mach-Zehnder point diffraction interferometer, are required. By these two fringes for two different wavelengths, the phase of a synthetic wavelength for the segmented telescope can be extracted using the digital holography technique. To overcome errors caused by atmosphere and measurement noises, the piston and tip/tilt coefficients for each segment of the telescope are acquired by fitting the plane from the phase of the synthetic wavelength in each segment of the telescope. The performance of the method is tested by co-phasing of a simulated telescope with 37 hexagonal segments with the existence of turbulence and noise. The numerical experimental results show that co-phasing of the segmented telescope with high accuracy can be achieved by dual wavelength digital holography.

This paper discusses the development of a demonstrator freeform active mirror for future astronomical instruments both on Earth and in space. It consists of a system overview and progress in various areas of technology in the building blocks of the mirror: an extreme freeform thin face sheet, an active array, design tools and the metrology and control of the system. The demonstrator aims to investigate the applicability of the technique in high end astronomical systems, also for space and cryogenically.

For more than two decades, Northrop Grumman Xinetics has been the principal supplier of small deformable mirrors that enable adaptive optical (AO) systems for the ground-based astronomical telescope community. With today’s drive toward extremely large aperture systems, and the desire of telescope designers to include adaptive optics in the main optical path of the telescope, Xinetics has recognized the need for large active mirrors with the requisite bandwidth and actuator stoke. Presented in this paper is the proposed use of Northrop Grumman Xinetics’ large, ultra-lightweight Silicon Carbide substrates with surface parallel actuation of sufficient spatial density and bandwidth to meet the requirements of tomorrow’s AO systems, while reducing complexity and cost.

JPCam is designed to perform the Javalambre-PAU Astrophysical Survey (J-PAS), a photometric survey of the northern sky with the new JST telescope being constructed in the Observatorio Astrofísico of Javalambre in Spain by CEFCA (Centro de Estudios de Física del Cosmos de Aragón). SENER has been responsible for the design, manufacturing, verification and delivery of the JPCam Actuator System that will be installed between the Telescope and the cryogenic Camera Subsystem. The main function is to control the instrument position to guarantee the image quality required during observations in all field of view and compensate deformations produced by gravity and temperature changes. The paper summarizes the main aspects of the hexapod design and earliest information related of integration and performances tests results.

The Interface Region Imaging Spectrograph (IRIS) is a complementary follow-on to Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO-AIA) and funded as a member of the NASA SMEX program. This paper presents the thermal design of the IRIS telescope front end, with a focus on the IRIS door and entrance aperture assembly. The challenge of the IRIS entrance aperture, including the door design, was to manage the solar flux, both before and after the door was opened. This is especially a problem with instruments that are permanently pointed directly at the sun. Though there is an array of effective flux-rejecting coatings, they are expensive, hard to apply, harder to measure, delicate, prone to unpredictable performance decay with exposure, and very often a source of contamination. This paper presents a thermal control and protection method based on robust, inexpensive coatings and materials, combined to produce high thermal and structural isolation. The end result is a first line of thermal protection whose performance is easy to predict and well isolated from the instrument it is protecting.

A cryogenic iris mechanism is under development as part of the ground calibration source for the SAFARI instrument. The iris mechanism is a variable aperture used as an optical shutter to fine-tune and modulate the absolute power output of the calibration source. It has 4 stainless steel blades that create a near-circular aperture in every position. The operating temperature is 4.5 Kelvin to provide a negligible background to the SAFARI detectors, and ‘hot spots’ above 9K should be prevented. Cryogenic testing proved that the iris works at 4K. It can be used in a broad range of cryogenic optical instruments where optical throughput needs to be controlled. Challenges in the design include the low cooling power available (5mW) and low friction at cryogenic temperatures. The actuator is an ‘arc-type’ rotary voice-coil motor. The use of flexural pivots creates a mono-stable mechanism with a resonance frequency at 26Hz. Accurate and fast position control with disturbance rejection is managed by a PID servo loop using a hall-sensor as input. At 4 Kelvin, the frequency is limited to 4Hz to avoid excess dissipation and heating. In this paper, the design and performance of the iris are discussed. The design was optimized using a thermal, magnetic and mechanical model made with COMSOL Finite Element Analysis software. The dynamical and state-space modeling of the mechanism and the concept of the electrical control are presented. The performance of the iris show good agreement to the analytical and COMSOL modeling.

To achieve the high adaptive optics sky coverage necessary to allow the GMT Integral-Field Spectrograph to access key scientific targets, the on-instrument adaptive-optics wavefront-sensing system must patrol the full 180 arcsecond diameter guide field passed to the instrument. Starlight must be held stationary on the wavefront sensor (accounting for flexure, differential refraction and non-sidereal tracking rates) to ~ 1 milliarcsecond to provide the stable position reference signal for deep AO observations and avoid introducing image blur. Hence a tight tolerance of 1/180,000 is placed on the positioning and encoding accuracy for the cryogenic On-Instrument Wave-Front Sensor feed. GMTIFS will achieve this requirement using a beam-steering mirror system as an optical relay for starlight from across the accessible guide field. The system avoids hysteresis and backlash by eliminating friction and avoiding gearing while maintaining high setting speed and accuracy with a precision feedback loop. Here we present the design of the relay system and the technical solution deployed to meet the challenging specifications for drive rate, accuracy and positional encoding of the beam-steering system.

The Mid-infrared E-ELT Imager and Spectrograph, or METIS, is foreseen as an early instrument for the European Extremely Large Telescope (E-ELT). A key part of METIS is the Cold Chopper (MCC) which switches the optical beam between the target and a nearby reference sky during observation for characterization of the fluctuating IR background signal in post-processing. This paper discusses the development and characterization of the realized MCC demonstrator. The chopper mirror (Ø64mm) should tip/tilt in 2D with a combined angle of up to 13.6mrad with 1.7μrad stability and repeatability within 5ms (95% duty cycle at 5Hz) at 80K. As these requirements cannot be met in the presence of friction or backlash, the mirror is guided by a monolithically integrated flexure mechanism. The angular position is actuated by three linear actuators and measured by three linear position sensors, resulting in a fast tip, tilt, and focus mirror. Using the third actuator introduces symmetry, and thus homogeneity in forces and heat flux. In an earlier paper, Ref. [1], the design of the chopper and the breadboard level testing of the key components were discussed. Since then, the chopper design has been revised to implement the lessons learned from the breadboard test and a demonstrator has been realized. This demonstrator has undergone an elaborate test program for characterization and performance validation in a cryogenic environment, as discussed in this paper.

In the context of the SAFARI instrument (SpicA FAR-infrared Instrument) SRON is developing a test environment to verify the SAFARI performance. The characterization of the detector focal plane will be performed with a backilluminated pinhole over a reimaged SAFARI focal plane by an XYZ scanning mechanism that consists of three linear stages stacked together. In order to reduce background radiation that can couple into the high sensitivity cryogenic detectors (goal NEP of 2•10^-19 W/√Hz and saturation power of few femtoWatts) the scanner is mounted inside the cryostat in the 4K environment. The required readout accuracy is 3 μm and reproducibility of 1 μm along the total travel of 32 mm. The stage will be operated in “on the fly” mode to prevent vibrations of the scanner mechanism and will move with a constant speed varying from 60 μm/s to 400 μm/s. In order to meet the requirements of large stroke, low dissipation (low friction) and high accuracy a DC motor plus spindle stage solution has been chosen. In this paper we will present the stage design and stage characterization, describing also the measurements setup. The room temperature performance has been measured with a 3D measuring machine cross calibrated with a laser interferometer and a 2-axis tilt sensor. The low temperature verification has been performed in a wet 4K cryostat using a laser interferometer for measuring the linear displacements and a theodolite for measuring the angular displacements. The angular displacements can be calibrated with a precision of 4 arcsec and the position could be determined with high accuracy. The presence of friction caused higher values of torque than predicted and consequently higher dissipation. The thermal model of the stage has also been verified at 4K.

Within Infra-Red large wavelength bandwidth instruments the use of mechanisms for selection of observation modes, filters, dispersing elements, pinholes or slits is inevitable. The cryogenic operating environment poses several challenges to these cryogenic mechanisms; like differential thermal shrinkage, physical property change of materials, limited use of lubrication, high feature density, limited space etc. MATISSE the mid-infrared interferometric spectrograph and imager for ESO's VLT interferometer (VLTI) at Paranal in Chile coherently combines the light from 4 telescopes. Within the Cold Optics Bench (COB) of MATISSE two concepts of selection mechanisms can be distinguished based on the same design principles: linear selection mechanisms (sliders) and rotating selection mechanisms (wheels).Both sliders and wheels are used at a temperature of 38 Kelvin. The selection mechanisms have to provide high accuracy and repeatability. The sliders/wheels have integrated tracks that run on small, accurately located, spring loaded precision bearings. Special indents are used for selection of the slider/wheel position. For maximum accuracy/repeatability the guiding/selection system is separated from the actuation in this case a cryogenic actuator inside the cryostat. The paper discusses the detailed design of the mechanisms and the final realization for the MATISSE COB. Limited lifetime and performance tests determine accuracy, warm and cold and the reliability/wear during life of the instrument. The test results and further improvements to the mechanisms are discussed.

The tip and tilt M5 mirror of the European Extremly Large Telescope (E-ELT) requires a demanding approach in light weighting. The approximately 3 m x 2.5 m elliptical plano mirror is specified to a weight of less than 500 kg with high Eigenfrequencies and low deformation under different inclination angles. In 2011 SCHOTT has presented a study to develop a design for the M5 mirror blank of the ESO E-ELT. The design presented was based on a radial square design to achieve the best compromise between performance and manufacturability. With the fabrication of a prototype section SCHOTT demonstrated its capability to manufacture the demanding features including pockets with 350 mm depth, thin walls and sloped pocket bottoms. Now 3 years later SCHOTT presents an iso-grid based design that is in accordance with the manufacturability progress that has been demonstrated in various ELZM (Extremely Lightweighted ZERODUR Mirrors) publications in the last two years. The achievements on the specified mechanical parameters are compared to the first approach from 2011. In this paper the results are presented and the performance parameters are discussed.

Within the Astronomical community there is growing interest in the development and use of very large aperture telescopes which will incorporate the latest advancements in optical materials. One of the most notable of these large size telescope projects, the Thirty Meter Telescope (TMT), will use mirror segments in the actively controlled primary mirrors and Ohara is a supplier of the near zero expansion mirror blanks. In this paper we present the measurement and inspection results on the initial 60 pieces of Ohara CLEARCERAM-Z HS 1.5m diameter blanks, which will be used for the TMT M1 Segment Blanks, including data on the Coefficient of Thermal Expansion (CTE), CTE uniformity, residual stress, bubbles and inclusions.

Segment production for the Giant Magellan Telescope is well underway, with the off-axis Segment 1 completed, off-axis Segments 2 and 3 already cast, and mold construction in progress for the casting of Segment 4, the center segment. All equipment and techniques required for segment fabrication and testing have been demonstrated in the manufacture of Segment 1. The equipment includes a 28 m test tower that incorporates four independent measurements of the segment's figure and geometry. The interferometric test uses a large asymmetric null corrector with three elements including a 3.75 m spherical mirror and a computer-generated hologram. For independent verification of the large-scale segment shape, we use a scanning pentaprism test that exploits the natural geometry of the telescope to focus collimated light to a point. The Software Configurable Optical Test System, loosely based on the Hartmann test, measures slope errors to submicroradian accuracy at high resolution over the full aperture. An enhanced laser tracker system guides the figuring through grinding and initial polishing. All measurements agree within the expected uncertainties, including three independent measurements of radius of curvature that agree within 0.3 mm. Segment 1 was polished using a 1.2 m stressed lap for smoothing and large-scale figuring, and a set of smaller passive rigid-conformal laps on an orbital polisher for deterministic small-scale figuring. For the remaining segments, the Mirror Lab is building a smaller, orbital stressed lap to combine the smoothing capability with deterministic figuring.

This paper will present the recent development achievements of a German SME supply chain to manufacture super lightweighted HB-Cesic^® mirrors for IR to visible applications. We will present recent design developments for achieving extreme light-weighted mirror substrates with extremely high stiffness and performance and in the second part the newly established German supply chain for the manufacturing of such extreme light-weighted mirror substrates.

Current strategies for detecting and deflecting/destroying small to medium size asteroids that may possibly enter earth’s atmosphere are in their infancy. Projects such as Sentinel for detection and DE-STAR for deflecting of asteroids are gaining momentum while others are in design stages. Single crystal silicon (SC-Si) with its unique set of mechanical and thermal properties is eminently suitable for deployment in any and all of these applications. But the superior thermal properties are particularly suited for high energy applications. We show that the exceptionally high thermal conductivity and diffusivity combined with relatively low thermal expansion enable SC-Si mirrors to handle the energy, often without active cooling, while maintaining figure. Both cooled and uncooled SC-Si mirrors have been employed successfully in high energy laser applications. For IR detection of asteroids, SC-Si lenses, prisms and filters are invaluable in the 1-5 μm range along with SC-Si mirrors at any wavelength. This space qualified material has zero defects and is readily available in a range of sizes to 300 mm diameter from several vendors, but while boules to 460 mm have limited availability, they can be obtained. For applications requiring larger sizes, McCarter’s proprietary glass frit bonding is utilized. Components approaching one meter have been produced.

Optical freeforms are increasingly gaining interest for optical systems like telescopes and spectrometers. This is a key topic of discussions for many years; however, the manufacturing process of freeform optics remains a challenging task whose complexity derives from the missing symmetry in freeform surfaces.

Ultra-precise manufacturing with diamond tools is an appropriate method to realize optical freeforms. Aspherical off axis mirrors machined similar to freeform or classical freeform mirrors like anamorphic mirrors can be fabricated in a deterministic process by using reference structures and correction loops. Diamond machining offers an excellent technology to meet the requirements regarding small values of surface deviation and low tolerances of position accuracy. Nevertheless, the typical micro-roughness of approximately 5 nm rms and the periodic turning structure set the limitation for diamond machined surfaces. The surfaces fulfill requirements for application in the Near Infrared (NIR) and Infrared (IR) spectral ranges, respectively. For smoothing the periodic structure, the diamond turning is combined with post polishing techniques like MRF (Magnetorheological Finishing) or computer assisted polishing. Therefore, the aluminum mirror has to be coated with amorphous nickel-phosphorous or silicon. Thus, the specification of applications in the visible (VIS) spectral range is reached. This process chain is interesting for a growing number of multi- and hyperspectral imaging devices such as telescopes and spectrometers based on all reflective metal optics.

The paper summarizes the fabrication of an optical bench for a high resolution IR telescope, discusses the results of post polishing mirrors for VIS telescopes, and shows an efficient and easy snap-together alignment strategy. The optical function of the TMA demonstrator built is an afocal imaging for a Limb-Sounder Instrument with a magnification of 4.5:1. Besides the design and manufacturing approach, the snap-together integration of the optical bench is presented, too. The presentation is finished with a forecast of a freeform IR telescope based on anamorphic mirrors.

At INAF-Astronomical Observatory of Brera a study is under way to explore the problems related to the ion beam figuring of full scale Zerodur hexagonal mirrors of M1 for the European Extremely Large Telescope (E-ELT), having size of 1.4 m corner to corner. During this study it is initially foreseen the figuring of a scaled down version mirror of the same material having size of 1 m corner to corner to assess the relevant figuring problems and issues. This specific mirror has a radius of curvature of 3 m, which allows for easy interferometric measurement. A mechanical support was designed to minimize its deformations due to the gravity. The Ion Beam Figuring Facility used for this study has been recently completed in the Brera Observatory and has a figuring area of 140 cm x 170 cm. It employs a Kaufman ion source having 50 mm grids mounted on three axis. This system has been designed and developed to be autonomous and self-monitoring during the figuring process. The software and the mathematical tools used to compute the dwell time solution have been developed at INAF-OAB as well. Aim of this study is the estimation and optimization of the time requested to correct the surface adopting strategies to mitigate the well-known thermal problems related to the Zerodur material. In this paper, the results obtained figuring the 1 m corner-to-corner test segment are reported.

The glass ceramic ZERODUR® from SCHOTT has an excellent reputation as mirror blank material for earthbound and space telescope applications. It is known for its extremely low coefficient of thermal expansion (CTE) at room temperature and its excellent CTE homogeneity. Recent improvements in CNC machining at SCHOTT allow achieving extremely light weighted substrates up to 90% incorporating very thin ribs and face sheets. In 2012 new ZERODUR® grades EXPANSION CLASS 0 SPECIAL and EXTREME have been released that offer the tightest CTE grades ever. With ZERODUR® TAILORED it is even possible to offer ZERODUR® optimized for customer application temperature profiles. In 2013 SCHOTT started the development of a new dilatometer setup with the target to drive the industrial standard of high accuracy thermal expansion metrology to its limit. In recent years SCHOTT published several paper on improved bending strength of ZERODUR® and lifetime evaluation based on threshold values derived from 3 parameter Weibull distribution fitted to a multitude of stress data. ZERODUR® has been and is still being successfully used as mirror substrates for a large number of space missions. ZERODUR® was used for the secondary mirror in HST and for the Wolter mirrors in CHANDRA without any reported degradation of the optical image quality during the lifetime of the missions. Some years ago early studies on the compaction effects of electron radiation on ZERODUR® were re analyzed. Using a more relevant physical model based on a simplified bimetallic equation the expected deformation of samples exposed in laboratory and space could be predicted in a much more accurate way. The relevant ingredients for light weighted mirror substrates are discussed in this paper: substrate material with excellent homogeneity in its properties, sufficient bending strengths, space radiation hardness and CNC machining capabilities.

In the development of thin active mirrors for future x-ray telescopes there is a need for full field, non-null methods of rapidly characterising highly distorted surfaces without contact. Phase measuring deflectometry, due to its high dynamic range and flexibility, is a promising solution to this problem. In this paper is described a system developed by the authors at University College London, as well as the results of surface measurements using this methodology on thin sheets of actuated glass.

Deflectometry is a well-known method for astronomical mirror metrology. This paper describes the method we developed for the characterization of free-form concave mirrors. Our technique is based on the synergy between deflectometry and ray-tracing. The deflectometrical test is performed by illuminating the reflecting surface with a known light pattern in a Ronchi – like configuration and retrieving the slope errors by the observed rays deflection. The ray-tracing code allows us to measure the slopes and to evaluate the mirror optical performance. This technique has two main advantages: it is fast and it is applicable on-site, as an intermediate step in the manufacturing process, preventing that out-of-specification mirrors may proceed towards further production steps. Thus, we obtain a considerable time and cost reduction.

As an example, we describe the results obtained measuring the primary mirror segments of the Cherenkov prototypal telescope manufactured by the Italian National Institute for Astrophysics in the context of the ASTRI Project. This specific case is challenging because the segmentation of the polynomial primary mirror lead to individual mirrors with deviations from the spherical optical design up to a few millimeters.

The Large Synoptic Survey Telescope (LSST) is a three-mirror wide-field survey telescope with the primary and tertiary mirrors on one monolithic substrate¹. This substrate is made of Ohara E6 borosilicate glass in a honeycomb sandwich, spin cast at the Steward Observatory Mirror Lab at The University of Arizona². Each surface is aspheric, with the specification in terms of conic constant error, maximum active bending forces and finally a structure function specification on the residual errors³. There are high-order deformation terms, but with no tolerance, any error is considered as a surface error and is included in the structure function. The radii of curvature are very different, requiring two independent test stations, each with instantaneous phase-shifting interferometers with null correctors. The primary null corrector is a standard two-element Offner null lens. The tertiary null corrector is a phase-etched computer-generated hologram (CGH). This paper details the two optical systems and their tolerances, showing that the uncertainty in measuring the figure is a small fraction of the structure function specification. Additional metrology includes the radii of curvature, optical axis locations, and relative surface tilts. The methods for measuring these will also be described along with their tolerances.

The baseline design of the European Extremely Large Telescope features a telescope with a 39-meter-class primary mirror (M1), consisting of 798 hexagonal segments. A measurement machine design is presented based on a non-contact single-point scanning technique, capable of measuring the form error of each segment with nanometer uncertainty, fast, and with low operational costs. The implementation of a tactile precision probe eliminates the need for the CMM in the earlier segment manufacturing process. Preliminary assessment show nanometer-level uncertainty after calibration.

We designed the interferometric test of a 300 mm flat mirror, based onto a spherical mirror and a dedicated CGH. The spherical beam of the interferometer is quasi collimated to the desired diameter by the spherical mirror, used slightly off-axis, and the CGH performs the residual wavefront correction. We performed tests on a 200 mm and 300 mm flat mirrors, and compared the results to the ones obtained by stitching, showing an accuracy well within the designed value. The possibility to calibrate the cavity by subtracting out the figure errors of the spherical mirror has also been evaluated.

Large telescope mirrors are typically measured using interferometry, which can achieve measurement accuracy of a few nanometers. However, applications of interferometry can be limited by small dynamic range, sensitivity to environment, and high cost. We have developed a range of surface measurement solutions using SCOTS, the Software Configurable Optical Test System, which illuminates the surface under test with light modulated from a digital display or moving source. The reflected light is captured and used to determine the surface slope which is integrated to provide the shape. A range of systems is presented that measures nearly all spatial scales and supports all phases of processing for large telescope mirrors.

Astronomical mirrors are key elements in modern optical telescopes, their dimensions are usually large and their specifications are demanding. Only a limited number of skilled companies respectively institutions around the world are able to master the challenge to polish an individual astronomical mirror, especially in dimensions above one meter. This paper presents an overview on the corresponding market including a listing of polishers around the globe. Therefore valuable information is provided to the astronomical community: Polishers may use the information as a global competitor database, astronomers and project managers may get more transparency on potential suppliers, and suppliers of polishing equipment may learn about unknown potential customers in other parts of the world. An evaluation of the historical market demand on large monolithic astronomical mirrors is presented. It concluded that this is still a niche market with a typical mean rate of 1-2 mirrors per year. Polishing of such mirrors is an enabling technology with impact on the development of technical know-how, public relation, visibility and reputation of the supplier. Within a corresponding technical discussion different polishing technologies are described. In addition it is demonstrated that strategic aspects and political considerations are influencing the selection of the optical finisher.

As part of the preparation for the arrival of the MUSE instrument to the VLT, it was required to adapt the hosting telescope (UT4) guide probe, to increase its back focal length. This is to allow enough space for the later deployment of the MUSE Adaptive Optics module GALACSI, in-between the telescope adapter rotator and the instrument itself. The UT guide probe is a critical component for the successful operation of the telescope, so its modification to increase the telescope’s back focal length, while maintaining full compatibility with the existing operation model and other hardware, was rather demanding. The design, manufacture, assembly and test for the new supporting arm in the UT guiding probe is presented. It mixes the use of novel materials (HB-CESIC® for the mirrors substrates) and state of the art manufacturing techniques (3D printing mould production and rapid casting for the support structure), which allow producing easily a high performance subsystem. Characterization of the system prior delivery to the telescope, its integration in the UT and results after commissioning is presented. Its successful implementation has validated new manufacturing techniques that may prove very useful for future instruments development.

MUSE (Multi Unit Spectroscopic Explorer) is a second generation Very Large Telescope (VLT) integral field spectrograph developed for the European Southern Observatory (ESO). It combines a 1’ x 1’ field of view sampled at 0.2 arcsec for its Wide Field Mode (WFM) and a 7.5"x7.5" field of view for its Narrow Field Mode (NFM). Both modes will operate with the improved spatial resolution provided by GALACSI (Ground Atmospheric Layer Adaptive Optics for Spectroscopic Imaging), that will use the VLT deformable secondary mirror and 4 Laser Guide Stars (LGS) foreseen in 2015. MUSE operates in the visible wavelength range (0.465-0.93 μm). A consortium of seven institutes is currently commissioning MUSE in the Very Large Telescope for the Preliminary Acceptance in Chile, scheduled for September, 2014.

MUSE is composed of several subsystems which are under the responsibility of each institute. The Fore Optics derotates and anamorphoses the image at the focal plane. A Splitting and Relay Optics feed the 24 identical Integral Field Units (IFU), that are mounted within a large monolithic structure. Each IFU incorporates an image slicer, a fully refractive spectrograph with VPH-grating and a detector system connected to a global vacuum and cryogenic system. During 2012 and 2013, all MUSE subsystems were integrated, aligned and tested to the P.I. institute at Lyon. After successful PAE in September 2013, MUSE instrument was shipped to the Very Large Telescope in Chile where that was aligned and tested in ESO integration hall at Paranal. After, MUSE was directly transported, fully aligned and without any optomechanical dismounting, onto VLT telescope where the first light was overcame the 7^th of February, 2014.

This paper describes the alignment procedure of the whole MUSE instrument with respect to the Very Large Telescope (VLT). It describes how 6 tons could be move with accuracy better than 0.025mm and less than 0.25 arcmin in order to reach alignment requirements. The success of the MUSE alignment is demonstrated by the excellent results obtained onto MUSE image quality and throughput directly onto the sky.

The High Efficiency and Resolution Multi Element Spectrograph (HERMES) is a four channel, VPH-grating spectrograph fed by two 400 fiber slit assemblies whose construction and commissioning has now been completed at the Anglo Australian Telescope (AAT). The size, weight, complexity, and scheduling constraints of the system necessitated that a fully integrated, deterministic, opto-mechanical alignment system be designed into the spectrograph before it was manufactured. This paper presents the principles about which the system was assembled and aligned, including the equipment and the metrology methods employed to complete the spectrograph integration.

Active optics for Space is relatively new field that takes advantage of lessons learnt on ground, and together with the tighter constrains of space environment it allows operation of larger mirrors apertures for space telescopes and better image quality. Technical developments are crucial to guarantee proper technological readiness for applications on new missions whose performance can be driven also by these novelties. This paper describes the philosophy pursued at ESA, providing an overview of the activities run within the Agency, as well as perspectives for new developments. The Optics Section of the Directorate of Technical and Quality Management of ESA/ESTEC is currently running three projects. Two examples are here addressed.

Over the past few years there has been remarkable success flying imaging telescope systems suspended from suborbital balloon payload systems. These imaging systems have covered optical, ultraviolet, sub-­‐millimeter and infrared passbands (i.e. BLAST, STO, SBI, Fireball and others). In recognition of these advances NASA is now considering ambitious programs to promote planetary imaging from high altitude at a fraction of the cost of similar fully orbital systems. The challenge with imaging from a balloon payload is delivering the full diffraction-­‐limited resolution of the system from a moving payload. Good progress has been made with damping mechanisms and oscillation control to remove most macroscopic movement in the departures of the imaging focal plane from a static configuration, however a jitter component remains that is difficult to remove using external corrections. This paper reports on work to demonstrate in the laboratory the utility and performance of actuating a detector focal plane (of whatever type) to remove the final jitter terms using an agile hexapod design. The input to this demonstration is the jitter signal generated by the pointing system of a previously flown balloon mission (the Stratospheric Terahertz Observatory, STO). Our group has a mature jitter compensation system that thermally isolates the control head from the focal plane itself. This allows the hexapod to remain at ambient temperature in a vacuum environment with the focal plane cooled to cryogenic temperatures. Our lab design mounts the focal plane on the hexapod in a custom cryostat and delivers an active optical stimulus together with the corresponding jitter signal, using the actuation of the hexapod to correct for the departures from a static, stable configuration. We believe this demonstration will make the case for inclusion of this technological solution in future balloon-­‐borne imaging systems requiring ultra-­‐high resolution.

We report the fabrication and characterization of prototype femtosecond-laser direct-written integrated photonic lanterns for operation in the mid-infrared (mid-IR). The devices were inscribed inside the bulk of a commercial gallium lanthanum sulphide (GLS) chalcogenide glass substrate and the characterization was performed using monochromatic light with a wavelength of 3.39 μm. We demonstrate that these proof-of-concept devices are capable of coupling specific multimode states of light into an array of single-modes, and vice-versa, with low-loss. In the future, instruments that utilize the single-moded output of such components may find applications in areas such as heterodyne spectroscopy, interferometry and remote sensing.

Integral field spectrographs have become mainstream instruments at modern telescopes because of their efficient way of collecting data-cubes. Image slicer based integral field spectrographs achieve the highest fill-factor on the detector, but due to the need to Nyquist-sample the spectra, their spatial sampling on the sky is rectangular. Using anamorphic pre-optics before the image slicer overcomes this effect further maximising the fill-factor, but introduces optical aberrations, throughput losses, and additional alignment and calibration requirements, compromising overall instrument performance. In this paper I present a concept for an image-slicer that achieves both spatial and spectral Nyquist-sampling without anamorphic pre-optics. Rotating each slitlet by 45° with respect to the dispersion direction, and arranging them into a saw-tooth pseudo-slit, leads to a lozenge shaped sampling element on the sky, however, the centres of the lozenges lie on a regular and square grid, satisfying the Nyquist sampling criterion in both spatial directions.

The Annular Groove Phase Mask (AGPM) is a circularly symmetric half wave plate consisting of a circular high aspect ratio sub-wavelength grating. Here we present a method for realizing such structures in diamond. To improve the AGPM performance, antireflective sub-wavelength gratings are etched on the backside of the components, and such gratings are also discussed. Components for the N-band (around 10 μm) and the L-band (around 3.8 μm) have been successfully fabricated. We are currently developing the process further to improve the precision of the gratings and produce an AGPM for the K-band (around 2.2 μm).

Starbugs are miniature piezoelectric ‘walking’ robots that can be operated in parallel to position many payloads (e.g. optical fibres) across a telescope’s focal plane. They consist of two concentric piezo-ceramic tubes that walk with micron step size. In addition to individual optical fibres, Starbugs have moved a payload of 0.75kg at several millimetres per second. The Australian Astronomical Observatory previously developed prototype devices and tested them in the laboratory. Now we are optimising the Starbug design for production and deployment in the TAIPAN instrument, which will be capable of configuring 300 optical fibres over a six degree field-of-view on the UK Schmidt Telescope within a few minutes. The TAIPAN instrument will demonstrate the technology and capability for MANIFEST (Many Instrument Fibre-System) proposed for the Giant Magellan Telescope. Design is addressing: connector density and voltage limitations, mechanical reliability and construction repeatability, field plate residues and scratching, metrology stability, and facilitation of improved motion in all aspects of the design for later evaluation. Here we present the new design features of the AAO TAIPAN Starbug.

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.

A GRISM, made of a grating on a prism, allow combining image and spectroscopy of the same field of view with the same optical system and detector, thus simplify instrument concept. New GRISM designs impose technical specifications difficult to reach with classical grating manufacturing processes: large useful aperture (>100mm), low groove frequency (<30g/mm), small blaze angle (<3°) and, last but not least, line curvature allowing wavefront corrections. In addition, gratings are commonly made of resin which may not be suitable to withstand the extreme space environment. Therefore, in the frame of a R&D project financed by the CNES, SILIOS Technologies developed a new resin-free grating manufacturing process and realized a first 80mm diameter prototype optically tested at LAM. We present detailed specifications of this resin-free grating, the manufacturing process, optical setups and models for optical performance verification and very encouraging results obtained on the first 80mm diameter grating prototype: >80% transmitted efficiency, <30nm RMS wavefront error, groove shape and roughness very close to theory and uniform over the useful aperture.

Silicon immersion gratings and grisms offer significant advantages in compactness and performance over frontsurface gratings and over grisms made from lower-index materials. At the same time, the high refractive index of Si (3.4) leads to very stringent constraints on the allowable groove position errors, typically rms < 20 nm over 100 mm and repetitive error of <5 nm amplitude. For both types of devices, we produce grooves in silicon using photolithography, plasma etching, and wet etching. To date, producers have used contact photolithography to pattern UV sensitive photoresist as the initial processing step, then transferred this pattern to a layer of silicon nitride that, in turn, serves as a hard mask during the wet etching of grooves into silicon.

For each step of the groove production, we have used new and sensitive techniques to determine the contribution of that step to the phase non-uniformity. Armed with an understanding of the errors and their origins, we could then implement process controls for each step. The plasma uniformity was improved for the silicon nitride mask etch process and the phase contribution of the plasma etch step was measured. We then used grayscale lithography, a technique in which the photoresist is deliberately underexposed, to measure large-scale nonuniformities in the UV exposure system to an accuracy of 3-5%, allowing us to make corrections to the optical alignment. Additionally, we used a new multiple-exposure technique combined with laser interferometry to measure the relationship between UV exposure dose and line edge shift. From these data we predict the contribution of the etching and photolithographic steps to phase error of the grating surface. These measurements indicate that the errors introduced during the exposure step dominate the contributions of all the other processing steps. This paper presents the techniques used to quantify individual process contributions to phase errors and steps that were taken to improve overall phase uniformity.

Due to their high efficiency and broad operational bandwidths, volume phase holographic gratings (VPHGs) are often the grating technology of choice for astronomical instruments, but current VPHGs exhibit a number of drawbacks including limits on their size, function and durability due to the manufacturing process. VPHGs are also generally made using a dichromated gelatine substrate, which exhibits reduced transmission at wavelengths longer than ~2.2 μm, limiting their ability to operate further into the mid-infrared. An emerging alternative method of manufacturing volume gratings is ultrafast laser inscription (ULI). This technique uses focused ultrashort laser pulses to induce a localised refractive index modification inside the bulk of a substrate material. We have recently demonstrated that ULI can be used to create volume gratings for operation in the visible, near-infrared and mid-infrared regions by inscribing volume gratings in a chalcogenide glass. The direct-write nature of ULI may then facilitate the fabrication of gratings which are not restricted in terms of their size and grating profile, as is currently the case with gelatine based VPHGs. In this paper, we present our work on the manufacture of volume gratings in gallium lanthanum sulphide (GLS) chalcogenide glass. The gratings are aimed at efficient operation at wavelengths around 1 μm, and the effect of applying an anti-reflection coating to the substrate to reduce Fresnel reflections is studied.

The develop of Volume Phase Holographic Gratings (VPHGs) working as echelle grating is reported based on binary structures. A mask lithography process was developed to produce the patterns on SU8 photoresist. The binary pattern with 50 l/mm were regular and defect free. The samples were characterized by different duty cycles, which is a key parameter in defining the diffraction efficiency in such binary gratings. The efficiency has been measured at different wavelengths and for different orders. The results have been compared with those obtained by simulations.

The Visible Integral-field Replicable Unit Spectrograph (VIRUS) is a baseline array of 150 copies of a simple, fiber-fed integral field spectrograph that will be deployed on the Hobby-Eberly Telescope (HET). VIRUS is the first optical astronomical instrument to be replicated on an industrial scale, and represents a relatively inexpensive solution for carrying out large-area spectroscopic surveys, such as the HET Dark Energy Experiment (HETDEX). Each spectrograph contains a volume phase holographic (VPH) grating with a 138 mm diameter clear aperture as its dispersing element. The instrument utilizes the grating in first-order for 350 < λ (nm) < 550. Including witness samples, a suite of 170 VPH gratings has been mass produced for VIRUS. Here, we present the design of the VIRUS VPH gratings and a discussion of their mass production. We additionally present the design and functionality of a custom apparatus that has been used to rapidly test the first-order diffraction efficiency of the gratings for various discrete wavelengths within the VIRUS spectral range. This device has been used to perform both in-situ tests to monitor the effects of adjustments to the production prescription as well as to carry out the final acceptance tests of the gratings' diffraction efficiency. Finally, we present the as-built performance results for the entire suite of VPH gratings.

The introduction of volume phase holographic (VPH) gratings into astronomy over a decade ago opened new possibilities for instrument designers. In this paper we describe an extension of VPH grating technology that will have applications in astronomy and beyond: curved VPH gratings. These devices can disperse light while simultaneously correcting aberrations. We have designed and manufactured two different kinds of convex VPH grating prototypes for use in off-axis reflecting spectrographs. One type functions in transmission and the other in reflection, enabling Offnerstyle spectrographs with the high-efficiency and low-cost advantages of VPH gratings. We will discuss the design process and the tools required for modelling these gratings along with the recording layout and process steps required to fabricate them. We will present performance data for the first convex VPH grating produced for an astronomical spectrograph.

We present innovative, immersed grating based optical designs for the SMO (Spectrograph Main Optics) module of the Mid-infrared E-ELT Imager and Spectrograph, METIS. The immersed grating allows a significant reduction of SMO volume compared to conventional echelle grating designs, because the diffraction takes place in high refractive index silicon. Additionally, using novel optimization techniques and technical solutions in silicon micromachining offered by the semiconductor industry, further improvements can be achieved. We show optical architectures based on compact, double-pass Three Mirror Anastigmat (TMA) designs, which appear advantageous in terms of one or several of the following: optical performance, reduction of volume, ease of manufacturing and testing. We explore optical designs, where the emphasis is put on manufacturability and we investigate optical solutions, where the ultimate goal is the highest possible optical performance. These novel, silicon immersed grating based design concepts are applicable for future earth and space based spectrometers.

Wide-Field Corrector designs are presented for the Blanco and Mayall telescopes, the CFHT and the AAT. The designs are Terezibh-style, with 5 or 6 lenses, and modest negative optical power. They have 2.2°-3° ields of view, with curved and telecentric focal surfaces suitable for fiber spectroscopy. Some variants also allow wide-field imaging, by changing the last WFC element. Apart from the adaptation of the Terebizh design for spectroscopy, the key feature is a new concept for a ‘Compensating Lateral Atmospheric Dispersion Corrector’, with two of the lenses being movable laterally by small amounts. This provides excellent atmospheric dispersion correction, without any additional surfaces or absorption. A novel and simple mechanism for providing the required lens motions is proposed, which requires just 3 linear actuators for each of the two moving lenses.

The image quality of a fluid atmospheric dispersion corrector (FADC) is analysed and presented. The FADC is located at Cassegrain focus to correct the atmospheric dispersion passively at Australian astronomical telescope. It is shown that an FADC with diameter 10mm can correct the atmospheric dispersion over a field diameter of 20” in the spectral range between 0.4μm to 1μm, and to zenith distance of 52º. The FADC image quality is well controlled within 0.27” for the telescope operation range. The residual atmospheric dispersion is 0.1” for on axis field and 0.20” at the extreme field (10”) at zenith distance of 52º. The FADC-induced shift in the centroids of the images is less than 10μm (0.067”). The FADC can work up to the field of 5’ at Cassegrain focus and its image quality is similar to its on axis performance. Our on-sky demonstration results agree well with our simulations.

Upcoming high-contrast imagers will all provide spectroscopic capabilities for the characterization of directly detected giant planets in wide orbits. While integral field spectroscopy (IFS) can provide both spatial and spectral information, it is usually limited in terms of field of view and resolution. The alternative is to use long slit spectroscopy coupled with coronagraphy (LSC), which can easily provide higher resolution and larger field of view. The SPHERE instrument for the VLT provides a LSC mode in its near-infrared imager and spectrograph, IRDIS. However, the fact that the occulting coronagraphic mask is merged in the focal plane with the slit reduces significantly its capacity to attenuate the diffraction, limiting the high-contrast capabilities of the instrument at close angular separations (0.3"-0.4"). To improve the diffraction suppression of the LSC in IRDIS, we recently proposed to use the stop-less Lyot coronagraph (SLLC) to build an apodized long slit coronagraph (ALSC), and we demonstrated that it improves notably the performance at small angular separation, allowing the spectral analysis of colder planets. The design of the SLLC apodizer has been optimized for an implementation in SPHERE/IRDIS, and it has recently been manufactured before being inserted into the instrument during reintegration of SPHERE in Paranal. In the current work, we present the final design of the SLLC apodizer, its specifications for the manufacturing step, and the first results obtained on SPHERE. We compare the results between the simple LSC and the new ALSC, and we draw the conclusions on the advantages and drawbacks of our design.

A Starshade is a sunflower-shaped satellite with a large inner disk structure surrounded by petals. A Starshade flies in formation with a space-borne telescope, creating a deep shadow around the telescope over a broad spectral band to permit nearby exoplanets to be viewed. Removing extraneous starlight before it enters the observatory optics greatly loosens the tolerances on the telescope and instrument that comprise the optical system, but the nature of the Starshade dictates a large deployable structure capable of deploying to a very precise shape. These shape requirements break down into key mechanical requirements which include the rigid-body position and orientation of each of the petals that ring the periphery of the Starshade. To verify our capability to meet these requirements, we modified an existing flight-like Astromesh reflector, provided by Northrup Grumman, as the base ring to which the petals attach. The integrated system, including 4 of the 30 flight-like subscale petals, truss, connecting spokes and central hub, was deployed tens of times in a flight-like manner using a gravity compensation system. After each deployment, discrete points in prescribed locations covering the petals and truss were measured using a highly-accurate laser tracker system. These measurements were then compared against the mechanical requirements, and the as-measured data shows deployment accuracy well within our milestone requirements and resulting in a contrast ratio consistent with exoplanet detection and characterization.

We present a novel application of optical tunneling in the context of high-angular resolution, high-contrast techniques with the aim of improving direct imaging capabilities of faint companions in the vicinity of bright stars. In contrast to existing techniques like coronagraphy, we apply well-established techniques from integrated optics to exclusively extinct a very narrow angular direction coming from the sky. This extinction is achieved in the pupil plane and does not suffer from diffraction pattern residuals. We give a comprehensive presentation of the underlying theory as well as first laboratory results.

The Apodizing Phase Plate (APP) is a phase-only pupil-plane coronagraph that suppresses starlight in a D-shaped region from 2 to 7 λ D around a target star. Its performance is insensitive to residual tip-tilt variations from the AO system and telescope structure. Using liquid crystal technology we develop a novel and improved version of the APP: the broadband vector Apodizing Phase Plate (vAPP). The vAPP prototype consists of an achromatic half-wave retarder pattern with a varying fast axis encoding phase structure down to 25 microns. The fast axis encodes the required phase pattern through the vector phase, while multiple twisting liquid crystal layers produce a nearly constant half-wave retardance over a broad bandwidth. Since pupil phase patterns are commonly designed to be antisymmetric, two complementary PSFs are produced with dark holes on opposite sides. We summarize results of the characterization of our latest vAPP prototype in terms of pupil phase reconstruction and PSF contrast performance. The liquid crystal patterning technique allows us to manufacture more extreme phase patterns than was possible before. We consider phase-only patterns that yield higher contrasts and better inner working angles than previous APPs, and patterns that produce dark regions 360 degrees around the PSF core. The possibility of including a phase ramp into the coronagraph is demonstrated, which simplifies the vAPP into a single optic. This additional phase ramp removes the need for a quarter-wave plate and a Wollaston prism, and enables the simplified implementation of a vAPP in a filter wheel at a pupil-plane location. Since the phase ramp is analogous to a polarization grating, it generates a (polarized) spectrum of a planet inside the dark hole, and thus allows for instantaneous characterization of the planet.

We present an innovative optical design for image slicer integral field unit (IFU) and manufacturing method which overcome optical limitation of metallic mirrors. Our IFU consists of micro image slicer of 45 arrayed highly-narrow flat metallic mirrors and a pseudo pupil mirror array of off-axis conic aspheres forming three pseudo slits of re-arranged slicer images. A prototype IFU demonstrates their optical quality high enough for a visible light spectrograph. The each slicer mirror is 1.58 mm in length and 30μm in width with surface roughness < 1 nm rms, edge sharpness < 0.1μm, etc. This IFU is small-sized and can be implemented in a multi-slit spectrograph without any moving mechanism and fore optics in which one slit is real and the others are of pseudo slits from the IFU. Those properties are well suitable for space-borne spectrograph to be aboard such as a next Japanese solar mission SOLAR-C.

Tornado Spectral Systems (TSS) has developed the High Throughput Virtual Slit (HTVS^TM), robust all-reflective pupil slicing technology capable of replacing the slit in research-, commercial- and MIL-SPEC-grade spectrometer systems. In the simplest configuration, the HTVS allows optical designers to remove the lossy slit from pointsource spectrometers and widen the input slit of long-slit spectrometers, greatly increasing throughput without loss of spectral resolution or cross-dispersion information. The HTVS works by transferring etendue between image plane axes but operating in the pupil domain rather than at a focal plane. While useful for other technologies, this is especially relevant for spectroscopic applications by performing the same spectral narrowing as a slit without throwing away light on the slit aperture. HTVS can be implemented in all-reflective designs and only requires a small number of reflections for significant spectral resolution enhancement–HTVS systems can be efficiently implemented in most wavelength regions. The etendueshifting operation also provides smooth scaling with input spot/image size without requiring reconfiguration for different targets (such as different seeing disk diameters or different fiber core sizes). Like most slicing technologies, HTVS provides throughput increases of several times without resolution loss over equivalent slitbased designs. HTVS technology enables robust slit replacement in point-source spectrometer systems. By virtue of pupilspace operation this technology has several advantages over comparable image-space slicer technology, including the ability to adapt gracefully and linearly to changing source size and better vertical packing of the flux distribution. Additionally, this technology can be implemented with large slicing factors in both fast and slow beams and can easily scale from large, room-sized spectrometers through to small, telescope-mounted devices. Finally, this same technology is directly applicable to multi-fiber spectrometers to achieve similar enhancement. HTVS also provides the ability to anamorphically “stretch” the slit image in long-slit spectrometers, allowing the instrument designer to optimize the plate scale in the dispersion axis and cross-dispersion axes independently without sacrificing spatial information. This allows users to widen the input slit, with the associated gain of throughput and loss of spatial selectivity, while maintaining the spectral resolution of the spectrometer system. This “stretching” places increased requirements on detector focal plane height, as with image slicing techniques, but provides additional degrees of freedom to instrument designers to build the best possible spectrometer systems. We discuss the details of this technology for an astronomical context, covering the applicability from small telescope mounted spectrometers through long-slit imagers and radial-velocity engines. This powerful tool provides additional degrees of freedom when designing a spectrometer, enabling instrument designers to further optimize systems for the required scientific goals.

MUSE (Multi Unit Spectroscopic Explorer) is a second generation Very Large Telescope (VLT) integral field spectrograph developed for the European Southern Observatory (ESO). It combines a 1’ x 1’ field of view sampled at 0.2 arcsec for its Wide Field Mode (WFM) and a 7.5"x7.5" field of view for its Narrow Field Mode (NFM). Both modes will operate with the improved spatial resolution provided by GALACSI (Ground Atmospheric Layer Adaptive Optics for Spectroscopic Imaging), that will use the VLT deformable secondary mirror and 4 Laser Guide Stars (LGS) foreseen in 2015. MUSE operates in the visible wavelength range (0.465-0.93 μm). A consortium of seven institutes is currently commissioning MUSE in the Very Large Telescope for the Preliminary Acceptance in Chile, scheduled for September, 2014. MUSE is composed of several subsystems which are under the responsibility of each institute. The Fore Optics derotates and anamorphoses the image at the focal plane. A Splitting and Relay Optics feed the 24 identical Integral Field Units (IFU), that are mounted within a large monolithic instrument mechanical structure. Each IFU incorporates an image slicer, a fully refractive spectrograph with VPH-grating and a detector system connected to a global vacuum and cryogenic system. During 2012 and 2013, all MUSE subsystems were integrated, aligned and tested to the P.I. institute at Lyon. After successful PAE in September 2013, MUSE instrument was shipped to the Very Large Telescope in Chile where it was aligned and tested in ESO integration hall at Paranal. After, MUSE was directly transferred in monolithic way onto VLT telescope where the first light was achieved. This paper describes the MUSE main optical component: the Field Splitter Unit. It splits the VLT image into 24 subfields and provides the first separation of the beam for the 24 Integral Field Units. This talk depicts its manufacturing at Winlight Optics and its alignment into MUSE instrument. The success of the MUSE alignment is demonstrated by the excellent results obtained onto MUSE positioning, image quality and throughput onto the sky. MUSE commissioning at the VLT is planned for September, 2014.

All spectrographs unavoidably scatter light. Scattering in the spectral direction is problematic for sky subtraction, since atmospheric spectral lines are blurred. Scattering in the spatial direction is problematic for fibre fed spectrographs, since it limits how closely fibres can be packed together. We investigate the nature of this scattering and show that the scattering wings have both a Lorentzian component, and a shallower (1/r) component. We investigate the causes of this from a theoretical perspective, and argue that for the spectral PSF the Lorentzian wings are in part due to the profile of the illumination of the pupil of the spectrograph onto the diffraction grating, whereas the shallower component is from bulk scattering. We then investigate ways to mitigate the diffractive scattering by apodising the pupil. In the ideal case of a Gaussian apodised pupil, the scattering can be significantly improved. Finally we look at realistic models of the spectrograph pupils of fibre fed spectrographs with a centrally obstructed telescope, and show that it is possible to apodise the pupil through non-telecentric injection into the fibre.

Spectroscopy is a technique of paramount importance to astronomy, as it enables the chemical composition, distances and velocities of celestial objects to be determined. As the diameter of a ground-based telescope increases, the pointspread- function (PSF) becomes increasingly degraded due to atmospheric seeing. A degraded PSF requires a larger spectrograph slit-width for efficient coupling and current spectrographs for large telescopes are already on the metre scale. This presents numerous issues in terms of manufacturability, cost and stability. As proposed in 2010 by Bland-Hawthorn et al, one approach which may help to improve spectrograph stability is a guided wave transition, known as a “photonic-lantern”. These devices enable the low-loss reformatting of a multimode PSF into a diffraction-limited source (in one direction). This pseudo-slit can then be used as the input to a traditional spectrograph operating at the diffraction limit. In essence, this approach may enable the use of diffractionlimited spectrographs on large telescopes without an unacceptable reduction in throughput. We have recently demonstrated that ultrafast laser inscription can be used to realize “integrated” photoniclanterns, by directly writing three-dimensional optical waveguide structures inside a glass substrate. This paper presents our work on developing ultrafast laser inscribed devices capable of reformatting a multimode telescope PSF into a diffraction-limited slit.

We present advances in the patented Echidna 'tilting spine' fiber positioner technology that has been in operation since 2007 on the SUBARU telescope in the FMOS system. The new Echidna technology is proposed to be implemented on two large fiber surveys: the Dark Energy Spectroscopic Instrument (DESI) (5000 fibers) as well the Australian ESO Positioner (AESOP) for 4MOST, a spectroscopic survey instrument for the VISTA telescope (~2500 fibers). The new 'superspine' actuators are stiffer, longer and more accurate than their predecessors. They have been prototyped at AAO, demonstrating reconfiguration times of ~15s for errors of <5 microns RMS. Laboratory testing of the prortotype shows accurate operation at temperatures of -10 to +30C, with an average heat output of 200 microwatts per actuator during reconfiguration. Throughput comparisons to other positioner types are presented, and we find that losses due to tilt will in general be outweighed by increased allocation yield and reduced fiber stress FRD. The losses from spine tilt are compensated by the gain in allocation yield coming from the greater patrol area, and quantified elsewhere in these proceedings. For typical tilts, f-ratios and collimator overspeeds, Echidna offers a clear efficiency gain versus current r-that or theta-phi positioners.

The Cobra fiber positioner is being developed by the California Institute of Technology (CIT) and the Jet Propulsion Laboratory (JPL) for the Prime Focus Spectrograph (PFS) instrument that will be installed at the Subaru Telescope on Mauna Kea, Hawaii. PFS is a fiber fed multi-object spectrometer that uses an array of Cobra fiber positioners to rapidly reconfigure 2394 optical fibers at the prime focus of the Subaru Telescope that are capable of positioning a fiber to within 5μm of a specified target location. A single Cobra fiber positioner measures 7.7mm in diameter and is 115mm tall. The Cobra fiber positioner uses two piezo-electric rotary motors to move a fiber optic anywhere in a 9.5mm diameter patrol area. In preparation for full-scale production of 2550 Cobra positioners an Engineering Model (EM) version was developed, built and tested to validate the design, reduce manufacturing costs, and improve system reliability. The EM leveraged the previously developed prototype versions of the Cobra fiber positioner. The requirements, design, assembly techniques, development testing, design qualification and performance evaluation of EM Cobra fiber positioners are described here. Also discussed is the use of the EM build and test campaign to validate the plans for full-scale production of 2550 Cobra fiber positioners scheduled to begin in late-2014.

MUSE (Multi Unit Spectroscopic Explorer) is a second generation Very Large Telescope (VLT) integral field spectrograph (1x1arcmin² Field of View) developed for the European Southern Observatory (ESO), operating in the visible wavelength range (0.465-0.93 μm). A consortium of seven institutes is currently commissioning MUSE in the Very Large Telescope for the Preliminary Acceptance in Chile, scheduled for September, 2014. MUSE is composed of several subsystems which are under the responsibility of each institute. The Fore Optics derotates and anamorphoses the image at the focal plane. A Splitting and Relay Optics feed the 24 identical Integral Field Units (IFU), that are mounted within a large monolithic instrument mechanical structure. Each IFU incorporates an image slicer, a fully refractive spectrograph with VPH-grating and a detector system connected to a global vacuum and cryogenic system. During 2012 and 2013, all MUSE subsystems were integrated, aligned and tested to the P.I. institute at Lyon. After successful PAE in September 2013, MUSE instrument was shipped to the Very Large Telescope in Chile where that was aligned and tested in ESO integration hall at Paranal. After, MUSE was directly transferred in monolithic way without dismounting onto VLT telescope where the first light was overcame. This talk describes the IFU Simulator which is the main alignment and performance tool for MUSE instrument. The IFU Simulator mimics the optomechanical interface between the MUSE pre-optic and the 24 IFUs. The optomechanical design is presented. After, the alignment method of this innovative tool for identifying the pupil and image planes is depicted. At the end, the internal test report is described. The success of the MUSE alignment using the IFU Simulator is demonstrated by the excellent results obtained onto MUSE positioning, image quality and throughput. MUSE commissioning at the VLT is planned for September, 2014.

We here report on recent progress on astronomical optical frequency comb generation at innoFSPEC-Potsdam and present preliminary test results using the fiber-fed Multi Unit Spectroscopic Explorer (MUSE) spectrograph. The frequency comb is generated by propagating two free-running lasers at 1554.3 and 1558.9 nm through two dispersionoptimized nonlinear fibers. The generated comb is centered at 1590 nm and comprises more than one hundred lines with an optical-signal-to-noise ratio larger than 30 dB. A nonlinear crystal is used to frequency double the whole comb spectrum, which is efficiently converted into the 800 nm spectral band. We evaluate first the wavelength stability using an optical spectrum analyzer with 0.02 nm resolution and wavelength grid of 0.01 nm. After confirming the stability within 0.01 nm, we compare the spectra of the astro-comb and the Ne and Hg calibration lamps: the astro-comb exhibits a much larger number of lines than lamp calibration sources. A series of preliminary tests using a fiber-fed MUSE spectrograph are subsequently carried out with the main goal of assessing the equidistancy of the comb lines. Using a P3d data reduction software we determine the centroid and the width of each comb line (for each of the 400 fibers feeding the spectrograph): equidistancy is confirmed with an absolute accuracy of 0.4 pm.

Lessons learnt during the design, integration and commissioning of the Southern African Large Telescope’s Fiber Instrument Feed and its guidance probe are presented along with initial on-sky performance results. Advances over the original design include enhanced target acquisition efficiency by including an imaging camera directly on the fiber-positioning stage, use of linear optical encoders on all motion stages, thermally compensated designs, a guidance probe optical design with much improved throughput as well as a new non-contact metrology process to accurately model the guider. The system has since been successfully used in commissioning the SALT High-Resolution Spectrograph.

Photonic lanterns are an important enabling technology for astrophotonics with a wide range of potential applications including fibre Bragg grating OH suppression, integrated photonic spectrographs and fibre scramblers for high resolution spectroscopy. The behaviour of photonic lanterns differs in several important respects from the conventional fibre systems more frequently used in astronomical instruments and a detailed understanding of this behaviour is required in order to make the most effective use of this promising technology. To this end we have undertaken a laboratory study of photonic lanterns with the aim of developing an empirical model for the mapping from input to output illumination distributions. We have measured overall transmission and near field output light distributions as a function of input angle of incidence for photonic lanterns with between 19 and 61 cores. We present the results of this work, highlight the key differences between photonic lanterns and conventional fibres, and illustrate the implications for instrument design via a case study, the design of the PRAXIS spectrograph. The empirical photonic lantern model was incorporated into an end-to-end PRAXIS performance model which was used to optimise the design parameters of the instrument. We describe the methods used and the resulting conclusions. The details of photonic lantern behaviour proved particularly important in selecting the optimum on sky field of view per fibre and in modelling of the instrument thermal background.

We report results of the extensive development work done on the 270-m optical fiber link for the GRACES project and a preliminary investigations into a high numerical aperture fiber for astronomy. The Gemini Remote Access CFHT ESPaDOnS Spectrograph (GRACES) is an instrumentation experiment to link ESPaDOnS, a bench-mounted highresolution optical spectrograph at CFHT, to the Gemini-North telescope with an optical fiber link. A 270-m fiber link with less than 14% Focal Ratio Degradation (FRD) has been developed jointly by HIA and FiberTech Optica for the experiment. A preliminary study has been conducted by HIA into a high numerical aperture fiber (0.26 numerical aperture) with the intended application of wide field optical spectrographs fiber fed from the telescope prime focus. The Laboratory test results of FRD, transmission, and stability for the GRACES fiber link and preliminary FRD measurements of the high numerical aperture fiber tests are reported.

The Steward Observatory Mirror Lab is nearing completion of the combined primary and tertiary mirrors of the Large Synoptic Survey Telescope. Fabrication of the combined mirror requires simulation of an active-optics correction that affects both mirror surfaces in a coordinated way. As is common for large mirrors, the specification allows correction of large-scale figure errors by a simulated bending of the substrate with the 156 mirror support actuators. Any bending affects both mirrors, so this active-optics correction is constrained by the requirement of bending the substrate so both mirrors meet their figure specifications simultaneously. The starting point of the simulated correction must be measurements of both mirrors with the substrate in the same shape, i. e. the same state of mechanical and thermal stress. Polishing was carried out using a 1.2 m stressed lap for smoothing and large-scale figuring, and a set of smaller passive rigid-conformal laps on an orbital polisher for deterministic small-scale figuring. The primary mirror is accurate to about 25 nm rms surface after the active-optics correction, while work continues toward completion of the tertiary.

The extended beacon belongs to partially coherent light field, and Phase space optics is an effective tool for analyzing such light field, especially in calculating the phase of multi-angle and multi-layer. Due to the lack of directly detection means, the research of this theory is crippled a long time, in this paper an optical structure to obtain the spectrogram which is a kind of phase space distribution has been presented, while the resolution problem and an improved method for possible has been discussed too, and two new methods to get high quality astronomical Image are appearing with such algorithm.

The existing force actuators cannot work properly in the Antarctic under the condition of low temperature. In this paper, a new design scheme of force actuator is put forward. Combined with the actual situation and the requirement of thin mirror active optical experiment system, we design the force actuator structure which combined the active support and passive support, and use a s-shaped load-cell to realize the force feedback controlling. Passive support part is responsible for the adjustment of large travel with low precision, and active support part driven by PZT is responsible for the adjustment with high accuracy. Finally, test was carried out through the open loop and closed loop experiment in low temperature environment. The experimental results show that: The force actuator’s output force is 120 ~ 280N, the accuracy is better than 0.05 N, meeting the requirement for the high precision under low temperature. The new kind of force actuator can be applied to the active optical support system in the Antarctic, and at the same time can also be applied to other structures of precision adjustment.

The next generation of space telescope will use large primary mirrors to achieve high angular resolution. Due to weight constrain, these large mirrors will have a very low mass per unit area. This ultra-light-weighting leads to deformations of the primary mirror optical surface due to gravity load difference between ground and space. Active Optics systems then become essential to maintain the quality of the output wavefront. The supporting structures and surface quality specifications of the mirror must be optimized regarding the active optics capabilities. The case of a two meters lightweight primary mirror will be presented.

The Large Synoptic Survey Telescope (LSST) is a large (8.4 meter) wide-field (3.5 degree) survey telescope, which will be located on the Cerro Pachón summit in Chile. Both the Secondary Mirror (M2) Cell Assembly and Camera utilize hexapods to facilitate optical positioning relative to the Primary/Tertiary (M1M3) Mirror. Geometric considerations preclude the use of a conventional hexapod arrangement for the M2 Hexapod. A rotator resides between the Camera and its hexapod to facilitate tracking. The requirements of the M2 Hexapod and Camera Hexapod are very similar; consequently to facilitate maintainability both hexapods will utilize identical actuators.

The design of the Large Millimeter Telescope (LMT/GTM) relies on an active surface system for the primary reflector in order to meet its surface accuracy specifications. Each of the 180 segments of the 50m diameter primary surface is supported by four linear actuators, one for each corner. Currently, while awaiting completion of the reflector panels needed to populate the outer portion of the surface, the precision reflecting surface is limited to the inner three rings of segments, which provide a 32.5m diameter primary with 84 segments. The interim active surface system must provide control for these segments long enough to allow completion of the rest of the reflecting surface and procurement and installation of the final actuators. During the LMT/GTM first light program in 2011, the interim active surface system of 336 actuators suffered from a wide range of problems that prevented useful operation. Following extensive diagnostic testing in 2012, the project implemented a substantial actuator improvement program in the first half of 2013, including mechanical modifications and replacement of the control system electronics. Later, each actuator was characterized on an external test bench, providing demonstration of actuator operation and readiness, as well as calibration information to further improve absolute accuracy. In this paper, we present results of the accuracy and repeatability of the refurbished actuators, as well as results from the accelerated lifetime testing on site. The uniformity of the calibration coefficients is also presented and discussed. The results demonstrate that the refurbished actuator units are sufficient for the needs of the interim active surface system.

The design of the Large Millimeter Telescope/Gran Telescopio Milimétrico (LMT/GTM) is such that it relies on an active surface system for the primary reflector in order to meet its surface accuracy specifications. Specifically, each of the primary surface segments is supported by four linear actuators, one for each corner. In the current state of the telescope, the interim active surface system must provide control for 84 segments long enough to allow completion of the rest of the reflecting surface and installation of the final actuators. During the LMT/GTM first light program in 2011, the interim active surface system of 336 actuators suffered from a wide range of problems that prevented useful operation. As a result, the LMT engineering team began an extensive testing program in 2012 to determine the sources of the problem and to evaluate possible mitigation strategies. As a result of these tests, the project implemented a substantial improvement program to the actuators in the first half of 2013, including a set of mechanical modifications and a replacement of the control system electronics. In this paper, we present the original mechanical design of the actuator, the design issues, and the modifications that were implemented. Details are provided about how the actuators have been improved from the perspective of repeatability, accuracy, and robustness. Finally, additional comments and recommendations are made for applying the lessons learned to the final actuator system.

Prior to the early science campaign of Spring 2013, the engineering team at the Large Millimeter Telescope/ Gran Telescopio Milimétrico (LMT/GTM) conducted a series of performance tests on the hexapod used for positioning the secondary reflector (M2 mirror). The tests were of particular interest to the project due to the high mass of the existing aluminum M2 mirror. The testing was conducted in a lower foundation room at the LMT site on a fixture that allowed the positioner and mirror to be oriented at both zenith and horizon orientations. In each of these positions, the repeatability of the system zero position was tested, along with both single degree-of-freedom (DOF) and combined DOF motions. Additionally, the tests investigated the stability of the system at constant command position to changes in the orientation of the unit with respect to gravity. Throughout these tests, a laser tracker was used for measurement of the position of targets on both the fixed base of the hexapod and on the outer rim of the M2 mirror. In this way, motions of the tracker head or of the support fixture could be eliminated from the analysis. In this paper, we present results of the accuracy and repeatability of the system, as well as comments on the effects of the laser tracker measurement geometry with respect to the system at the zenith and horizon orientations.

As radio telescopes have reached larger diameters and higher frequencies, it is typically not possible to meet their surface accuracy specifications using passive homology-based designs. The most common solution to this problem in the current generation of large, high-frequency radio telescopes is to employ a system of linear actuators to correct the surface shape of the primary reflector. The exact specifications of active surface actuators vary with the telescope. However, they have many common features, some of which drive their design. In general, these actuators must provide precise and repeatable positioning under significant loads during operation and they must withstand even higher loads for survival conditions. For general safety, they typically must hold position in the event of a power failure and must incorporate position limits, whether electrical, mechanical, or both. Because the number of actuators is generally high for large active surfaces (hundreds or even thousands of actuators), they must also be reliable and of reasonable individual cost. Finally, for maximum flexibility in their installation, they must be compact. This paper presents a concept for an active surface actuator based on a form-closed eccentric cam (kinematically, a Scotch Yoke mechanism). Such a design is limited in stroke, but offers potential advantages in terms of manufacture, compactness, measurement, and survival loading. The paper demonstrates that some of the expected advantages cannot be practically realized, due to dimensions that are driven by survival loading conditions. As a result, this concept is likely to offer an advantage over conventional screw-type actuators only for cases where actuator runaway and stall are the driving considerations.

A high dynamic range imaging method of GEO staring imaging is proposed based on radiance simulation of GEO remote sensing targets and analysis of foreign and domestic remote sensing payload characteristics. Due to the high temporal resolution of GEO staring imaging, multiple exposure method is used and image sequences are captured with different integration times; Then a high dynamic range image is obtained after fusion with the contrast of neighborhood pixel values being the weighting factor. Finally experiments are done in lab with visible plane array 2048*2048 imaging system for verifying multiple exposure test. It can be proved that using multiple exposure capture fusion method can obtain an 11 bit high dynamic range image. The essence of the method is that it sacrifices time resolution in exchange for high dynamic range, which overcomes the defect of small dynamic range of single exposure and is of practical significance in terms of GEO high dynamic range information capture.

The Secondary Mirror System (M2S) and Tertiary Mirror System (M3S) of the Thirty Meter Telescope (TMT) consist of passively mounted mirrors supported in kinematic cell assemblies that are moved during telescope tracking to counteract effects of changing zenith angle and thermal gradients within the telescope structure. TMT is concerned that the requirements for pointing jitter during Adaptive Optics tracking for the M2 and M3 Systems are very challenging with a risk of requiring complex stabilization systems for compliance. Both systems were researched to determine whether similar un-stabilized hardware exists that can meet the TMT jitter requirements. Tests using representative TMT tracking motions were then performed to measure jitter on similar existing hardware. The results of these hardware tests have been analyzed. Test results, remaining risk assessment and further testing plans are presented.

We study a novel active optics control scheme at the VST on Cerro Paranal, an f/5:5 survey telescope with a 1x1 degree field of view and a 2.6m primary mirror. This scheme analyzes the elongation pattern of the star PSFs across the full science image (267 Mpixels) and compares their second moments with an analytical model based on 5th-order geometrical optics, comprising 9 degrees of freedom in mirror misalignments and deformations. Using a numerical optimization method, we can complete the star extraction and fitting process in under one minute, fast enough for effective closed-loop active optics control in survey observing cadences.

One of the fundamental design principles of the LMT is that its segmented primary surface must be active: the position and orientation of each of the segments must be moved in order to maintain the precise parabolic surface that is required by the specifications. Consequently, a system of actuators, one at the corner of each segment, is used to move the segments to counteract surface deformations attributed to gravity or thermal effects.

A new control system was designed and built within the project to implement an active surface at the LMT. The technical concept for the active surface control system is to provide a set of bus boxes with built-in control and I/O capabilities to run four actuators each. Bus boxes read the LVDT sensor position and limit switch status for each actuator and use this information to drive the actuator’s DC motor, closing the position loop. Each bus box contains a DC power supply for the electronics, a second DC power supply for the motors, an embedded controller with I/O to close the position loop, and a custom printed circuit board to condition the LVDT signals and drive the motors. An interface printed circuit board resides in each actuator providing a single connector access to the LVDT, the motor, and the limit switches. During the fall of 2013, 84 bus boxes were commissioned to control the 336 actuators of the inner three rings of the telescope. The surface correction model was determined using holography measurements and the active surface system has been in regular use during the scientific observation at the LMT.

The Large Synoptic Survey Telescope (LSST) utilizes active optics on its three mirrors to maintain image quality. This paper describes the philosophy behind the design and characterization of the inner loop controllers for the LSST project. A custom approach was selected in order to satisfy the stringent requirements of the active optics control system resulting in a very low power, robust and compact solution. The tough metrology requirements were translated into an analog front end capable of performing with high accuracy under the varying ambient conditions, mainly temperature. Networking capabilities are embedded in the design to adapt to different distributed control configurations. All basic applications and some additional uses are discussed, and test results are presented.

In this paper we present the design of freeform mirror based optical systems that have the potential to be used in future astronomical instrumentation in the era of extremely large ground based telescopes. Firstly we describe the optical requirements followed by a summary of the optimization methodology used to design the freeform surface. The intention is to create optical architectures, which not only have the numerous advantages of freeform based systems (increased optical performance and/or reduction of mass and volume), but also can be manufactured and tested with today’s manufacturing techniques and technologies. The team plans to build a demonstrator based on one of the optical design examples presented in this paper. The demonstrator will be built and tested as part of the OPTICON FP7 Freeform Active Mirror Experiment (FAME) project. A hydroforming technique developed as part of the previous OPTICON FP7 project will be used to produce an accurate, compact and stable freeform mirror. The manufacturing issues normally experienced in the production of freeform mirrors are solved through the hydroforming of thin polished substrates, which then will be supported with an active array structure. The active array will be used to compensate for residual manufacturing errors, thermo-elastic deformation and gravity-induced errors.

In this paper a status report is given on the development of the FAME (Freeform Active Mirror Experiment) active array. Further information regarding this project can be found in the paper by Venema et al. (this conference). Freeform optics provide the opportunity to drastically reduce the complexity of the future optical instruments. In order to produce these non-axisymmetric freeform optics with up to 1 mm deviation from the best fit sphere, it is necessary to come up with new design and manufacturing methods. The way we would like to create novel freeform optics is by fine tuning a preformed high surface-quality thin mirror using an array which is actively controlled by actuators. In the following we introduce the tools deployed to create and assess the individual designs. The result is an active array having optimal number and lay-out of actuators.

We present the conception of an anamorphic and telecentric scale changer with no distortion, able to provide magnifications in the range of 2 to 30 without any interchangeable optics, dedicated to ground or space applications. Several optical designs are investigated and the final configuration is based on off-axis five mirrors system with no moving elements. Four active mirrors are adapted to four different zoom configurations. A specific mechanical profile with variable thickness distribution is simulated and optimized on each mirror to allow using a minimal number of actuators. An opto-mechanical design will be presented, showing the implementation of actuators on the system. This work is done in the frame of the ANR project OASIX and will produce a lab prototype in 2015.

ZERODUR^® glass ceramic from SCHOTT is known for its very low thermal expansion coefficient (CTE) at room temperature and its excellent CTE homogeneity. It is widely used for ground-based astronomical mirrors but also for satellite applications. Many reference application demonstrate the excellent and long lasting performance of ZERODUR^® components in orbit. For space application a low CTE of the mirror material is required at cryogenic temperatures together with a good match of the thermal expansion to the supporting structure material. It is possible to optimize the coefficient of thermal expansion of ZERODUR^® for cryogenic applications. This paper reports on measurements of thermal expansion of ZERODUR^® down to cryogenic temperatures of 10 K performed by the PTB (Physikalisch Technische Bundesanstallt, Braunschweig, Germany, the national metrology laboratory). The ZERODUR^® TAILORED CRYO presented in this paper has a very low coefficient of thermal expansion down to 70 K. The maximum absolute integrated thermal expansion down to 10 K is only about 20 ppm. Mirror blanks made from ZERODUR^® TAILORED CRYO can be light weighted to almost 90% with our modern processing technologies. With ZERODUR^® TAILORED CRYO, SCHOTT offers the mirror blank material for the next generation of space telescope applications.

In a continuous effort since 2007 a considerable amount of new data and information has been gathered on the bending strength of the extremely low thermal expansion glass ceramic ZERODUR^®. By fitting a three parameter Weibull distribution to the data it could be shown that for homogenously ground surfaces minimum breakage stresses exist lying much higher than the previously applied design limits. In order to achieve even higher allowable stress values diamond grain ground surfaces have been acid etched, a procedure widely accepted as strength increasing measure. If surfaces are etched taking off layers with thickness which are comparable to the maximum micro crack depth of the preceding grinding process they also show statistical distributions compatible with a three parameter Weibull distribution. SCHOTT has performed additional measurement series with etch solutions with variable composition testing the applicability of this distribution and the possibility to achieve further increase of the minimum breakage stress. For long term loading applications strength change with time and environmental media are important. The parameter needed for prediction calculations which is combining these influences is the stress corrosion constant. Results from the past differ significantly from each other. On the basis of new investigations better information will be provided for choosing the best value for the given application conditions.

Large telescope mirrors have stringent requirements for surface irregularity on all spatial scales. Large scale errors, typically represented with Zernike polynomials, are relatively easy to control. Errors with smaller spatial scale can be more difficult because the specifications are tighter. Small scale errors are controlled with a combination of natural smoothing from large tools and directed figuring with precisely controlled small tools. The optimization of the complete process builds on the quantitative understanding of natural smoothing, convergence of small tool polishing, and confidence in the surface measurements. This paper provides parametric models for smoothing and directed figuring that can be used to optimize the manufacturing process.

The Observatoire de Paris is constructing a prototype Small-Sized Telescope (SST) for the Cherenkov Telescope Array (CTA), named SST-GATE, based on the dual-mirror Schwarzschild-Couder optical design. Considering the mirrors size and its specific curvature and the optical requirements for the Cherenkov imaging telescope, a non-conventional process has been used for designing and manufacturing the mirrors of the SST-GATE prototype. Based on machining, polishing and coating of aluminium bulk samples, this process has been validated by simulation and tests that will be detailed in this paper after a discussion on the Schwarzschild-Couder optical design which so far has never been used to design ground based telescopes. Even if the SST-GATE is a prototype for small size telescopes of the CTA array, the primary mirror of the telescope is 4 meters diameter, and it has to be segmented. Due to the dual-mirror configuration, the alignment is a complex task that needs a well defined and precise process that will be discussed in this paper.

The next generation of imaging atmospheric Cherenkov telescopes will require the production of thousands of mirror segments; an unprecedented amount of optical surface. To accomplish this, the Italian Istituto Nazionale di AstroFisica (INAF) has recently developed a successful technique. This method, called glass cold-shaping, is mainly intended for the manufacturing of mirrors for optical systems with an angular resolution of a few arcminutes, intended to operate in extreme environments. Its principal mechanical features are very low weight and high rigidity of the resulting segments, and its cost and production time turn out to be very competitive as well. The process is based on the shaping of thin glass foils by means of forced bending at room temperature; a sandwich structure is then assembled for retaining the imposed shape. These mirrors are composted of commercial, off-the-shelf materials. In this contribution we give an overview of the latest results achieved in the manufacturing of the pre-production series of mirrors for the Medium Size and Small Size Telescopes of the Cherenkov Telescope Array observatory.

Thin glass foils are considered good candidates to build a segmented X-ray telescope with effective area as large as 2 m² and angular resolution better than 5 arcsec. In order to produce thin glass mirror segments, we developed a direct hot slumping technique assisted by pressure, in which the shape of a mould is replicated onto the optical surface of the glass. In this paper we present the result obtained with AF32 (by Schott) and EAGLE XG (by Corning) glass types. The selected mould material is Zerodur K20, as it does not require any anti-sticking layer and has a good matching, in terms of Coefficient of Thermal Expansion, with both glass types. Our group already produced a few prototypes, reaching angular resolution near 20 arcsec. In this work, relevant steps forward aimed at attaining a 5 arcsec angular resolution are described, along with the tuning of few key parameters in the slumping process. The results obtained on a newly procured cylindrical Zerodur K20 mould are presented.

In this report we describe our development of a prototype inverse-polished mirror for the passive correction of the static and predictable wavefront errors (WFE) of space-based telescopes, in particular, especially for infrared coronagraphs. An artificial WFE pattern with a root mean square (rms) value of 350 nm was numerically generated to facilitate the design of the prototype mirror. The surface of the mirror is approximately flat, is 50.0 mm in diameter and 15.0 mm thick at the edge. The designed WFE pattern was constructed on the mirror surface by micro-polishing. Both the figure and roughness of the mirror surface were evaluated. The rms value of the measured surface figure was reduced to 135 nm after subtraction of the designed surface figure. The benefit of subtraction to mid-infrared coronagraph performance was simulated, which showed the contrast was improved by a factor of ~100 close to the core (closer than 10 λ/D where λ and D are the wavelength and telescope aperture diameter, respectively) of the coronagraphic image of a point source. An analysis of the power spectrum density shows that the lower frequencies in the WFE are well reproduced on the mirror, while the higher frequencies remain due to the limitations imposed on the controllable spatial resolution by the fabrication process. In this study, inverse-polished mirrors combined with deformable mirrors and their application to ground-based telescopes are also discussed. To fully explore the potential of the inverse-polished mirror, a systematic allocation of the error budget is essential taking into account not only the fabrication accuracy of the mirror but also an evaluation of the telescope and other factors with non-predictable uncertainties.

We report the development of optical mirrors based on polymer matrix composite materials. Advantages of this technology are low cost and versatility. By using appropriate combinations of polymers and various metallic and nonmetallic particles and fibers, the properties of the materials can be tailored to suit a wide variety of applications. We report the fabrication and testing of flat and curved mirrors made with metal powders, multiple mirrors replicated with high degree of uniformity from the same mandrels, cryogenic testing, mirrors made of ferromagnetic materials that can be actively or adaptively controlled by non-contact actuation, optics with very smooth surfaces made by replication, and by spincasting. We discuss development of a new generation of ultra-compact, low power active optics and 3D printing of athermal telescopes.

The Daniel K. Inouye Solar Telescope (DKIST, formerly the Advanced Technology Solar Telescope, ATST) will be the most powerful solar telescope in the world. It is currently being built by the Association of Universities for Research in Astronomy (AURA) in a height of 3000 m above sea level on the mountain Haleakala of Maui, Hawaii. The primary mirror blank of diameter 4.26 m is made of the extremely low thermal expansion glass ceramic ZERODUR® of SCHOTT AG Advanced Optics. The DKIST primary mirror design is extremely challenging. With a mirror thickness of only 78 to 85 mm it is the smallest thickness ever machined on a mirror of 4.26 m in diameter. Additionally the glassy ZERODUR® casting is one of the largest in size ever produced for a 4 m class ZERODUR® mirror blank. The off axis aspherical mirror surface required sophisticated grinding procedures to achieve the specified geometrical tolerance. The small thickness of about 80 mm required special measures during processing, lifting and transport. Additionally acid etch treatment was applied to the convex back-surface and the conical shaped outer diameter surface to improve the strength of the blank. This paper reports on the challenging tasks and the achievements on the material property and dimensional specification parameter during the production of the 4.26 m ZERODUR® primary mirror blank for AURA.

The curing of epoxy adhesives is a complex phenomenon where the thermal, the chemistry and the mechanics are coupled. Corresponding material properties such as mechanical and physics properties are evolving with the curing. This paper focuses on their predictions by a multiphisics FEM approach of the thermal, chemical and mechanical couplings involved by the curing for a novel assembly of radio telescope panel. The first part presents the constitutive model of an epoxy adhesive that is considered for the curing. The numerical solving, performed with a specific user subroutine of Ansys, is detailed and allows the study of real three-dimensional structure parts. Residual stresses and strains of different metallic membranes and internal adhesives in the interconnect during the assembly of radio telescope panel are investigated. The mechanical response of the interconnect is analyzed with respect to the poisson’s ratio, relaxation time and adhesive thickness. It is shown that, although the overall residual stresses at the interconnect increase with the adhesive curing, the local strains have different evolving trends, indicating the possibility of damage and decohesion that might compromise mechanical integrity and interrupt the component processing precision.

Extreme freeform mirrors couple a non-axisymmetrical shape and an extreme asphericity, i.e. more than one millimeter of deviation from the best fit sphere. In astronomical instrumentation, such a large asphericity allows compact instruments, using less optical components. However, the lack of freeform mirrors manufacturing facilities is a real issue. We present the concept and development of an innovative manufacturing process based on plasticity forming which allow imprinting permanent deformations on mirrors, following a pre-defined mold. The aim of this activity, pursued in the frame of the OPTICON-FAME (Freeform Active Mirrors Experiment) project, is to demonstrate the suitability of this method for VIS/NIR/MIR applications. The process developed can operate on thin and flat polished initial substrates. Three study cases have been highlighted by FEA (Finite Element Analysis) and the real tests associated were performed on thin substrates in AISI420b stainless steel with 100 mm optical diameter. A comparison between FEA and tests is performed to study the evolution of the mechanical behaviour and the optical quality. The opto-mechanical results will allow a fine tuning of FEA parameters to optimize the residual form errors obtained through this process to converge toward an innovative and recurrent process.

The surface accuracy of astronomical telescope focal plate is a key indicator to precision stellar observation. To conduct accurate deformation measurement for focal plate in different status, a 6-DOF hexapod platform was used for attitude adjustment. For the small adjustment range of a classic 6-DOF hexapod platform, an improved structural arrangement method was proposed in the paper to achieve ultimate adjustment of the focal plate in horizontal and vertical direction. To validate the feasibility of this method, an angle change model which used ball hinge was set up for the movement and base plate. Simulation results in MATLAB suggested that the ball hinge angle change of movement and base plate is within the range of the limiting angle in the process of the platform plate adjusting to ultimate attitude. The proposed method has some guiding significance for accurate surface measurement of focal plate.

Ultra-precise metal optics are key components of sophisticated scientific instruments in astronomy and space applications. Especially for cryogenic applications, a detailed knowledge and the control of the coefficient of thermal expansion (CTE) of the used materials are essential. Reflective optical components in IR- and NIR-instruments primarily consist of the aluminum alloy Al6061. The achievable micro-roughness of diamond machined and directly polished Al6061 does not fulfill the requirements for applications in the visible spectral range. Electroless nickel enables the reduction of the mirror surface roughness to the sub-nm range by polishing. To minimize the associated disadvantageous bimetallic effect, a novel material combination for cryogenic mirrors based on electroless nickel and hypereutectic aluminum-silicon is investigated. An increasing silicon content of the aluminum material decreases the CTE in the temperature range to be considered. This paper shows the CTE for aluminum materials containing about 42 wt% silicon (AlSi42) and for electroless nickel with a phosphorous content ranging from 10.5 to 13 %. The CTE differ to about 0.5 × 10^-6 K^-1 in a temperature range from -185 °C (LN₂) to 100 °C. Besides, the correlations between the chemical compositions of aluminum-silicon materials and electroless nickel are shown. A metrology setup for cryo-interferometry was developed to analyze the remaining and reversible shape deviation at cryogenic temperatures. Changes could be caused by different CTE, mounting forces and residual stress conditions. In the electroless nickel layer, the resulting shape deviation can be preshaped by deterministic correction processes such as magnetorheological finishing (MRF) at room temperature.

We have been developing a rotating mechanism and a linear motion mechanism for their usage in contamination sensitive space telescopes. They both are needed for ~1.4 meter optical telescope and its focal plane instrument onboard SOLAR-C, the next-generation spaceborne solar observatory following Hinode. Highly reliable long life performance, low outgassing properties, and low level of micro-vibration are required along with their scientific performance. With the proto-type mechanisms, the long life performance and outgassing properties of the mechanisms have been evaluated in vacuum chambers. The level of micro-vibration excited during the operations of the rotating mechanism was measured by operating it on the Kestler table. This paper provides the overall descriptions of our mechanism developments.

The quality of space telescope observations greatly depends on the pointing performance of the spacecraft. In this paper, recent advances in star tracker algorithms are discussed. This paper discusses efficient star tracker algorithms that improve the pointing performance of the satellite, resulting in observations of higher quality. Furthermore, the greatly reduced computational cost of these algorithms facilitates the inclusion of astronomical payload measurements in the attitude determination and control loop. When the payload is used as an additional star tracker, the pointing performance of the spacecraft increases drastically, which in its turn improves the quality of the scientific measurements. Simulations show that with these improvements, the absolute pointing error of the spacecraft can be reduced considerably.

Antarctic is perfect site for astronomic observatory. But Antarctic also challenge the telescope design because of low temperature. The low temperature can impact characterization of telescope control system, especially for drive system. The following phenomenon can be produced due to low temperature. 1. The viscosity of grease will increase. 2. The clearance of bearing and gear will decrease. These two factors can lead to the increase in load torque of drive system with temperature drop. This would cause the bad tracking accuracy and low speed creeping. In order to overcome the impact of low temperature and improve the telescope’s track accuracy. In this paper, we describe some methods to overcome the effect of low temperature. First, the motor’s electromagnetism and lubrication in low temperature are analyzed. It shows that motor’s electromagnetism is little affected by temperature if the suitable material is selected. But the characterization of grease change dramatically with temperature. Second, the other lubricant material, solid lubricant, instead of lubricating grease is proposed. Contrasting experiment on two lubricant material proved that the solid lubricant is better than lubricating grease in low temperature environment. Third, besides the mechanical solution, a method from control point view is proposed to reduce the temperature influence. In this paper, the friction feedforward algorithm is used to compensate the torque change. Laboratory testing results will be presented verifying that friction feedforward can increase the tracking accuracy in low temperature environment.

GRAVITY is a second generation VLTI instrument for high-precision narrow-angle astrometry and phase-referenced interferometric imaging in the astronomical K-band. The cryostat of the beam combiner instrument provides the required temperatures for the various subunits ranging from 40K to 290K with a milli-Kelvin temperature stability for some selected units. The bath cryostat is cooled with liquid nitrogen and makes use of the exhaust gas to cool the main optical bench to an intermediate temperature of 240K. The fringe tracking detector will be cooled separately by a single-stage pulse tube cooler to a temperature of 40K. The pulse tube cooler is optimized for minimum vibrations. In particular its warm side is connected to the 80K reservoir of the LN2 cryostat to minimize the required input power. All temperature levels are actively stabilized by electric heaters. The cold bench is supported separately from the vacuum vessel and the liquid nitrogen reservoir to minimize the transfer of acoustic noise onto the instrument.

The LSST Camera has a higher cryogenic heat load than previous CCD telescope cameras due to its large size (634 mm diameter focal plane, 3.2 Giga pixels) and its close coupled front-end electronics operating at low temperature inside the cryostat. Various refrigeration technologies are considered for this telescope/camera environment. MMR-Technology’s Mixed Refrigerant technology was chosen. A collaboration with that company was started in 2009. The system, based on a cluster of Joule-Thomson refrigerators running a special blend of mixed refrigerants is described. Both the advantages and problems of applying this technology to telescope camera refrigeration are discussed. Test results from a prototype refrigerator running in a realistic telescope configuration are reported. Current and future stages of the development program are described.