From the ardent bucklers used during the Syracuse battle to set fire to Romans’ ships to more contemporary piezoelectric
deformable mirrors widely used in astronomy, from very large voice coil deformable mirrors considered in future
Extremely Large Telescopes to very small and compact ones embedded in Multi Object Adaptive Optics systems, this
paper aims at giving an overview of Deformable Mirror technology for Adaptive Optics and Astronomy.
First the main drivers for the design of Deformable Mirrors are recalled, not only related to atmospheric aberration
compensation but also to environmental conditions or mechanical constraints. Then the different technologies available
today for the manufacturing of Deformable Mirrors will be described, pros and cons analyzed. A review of the
Companies and Institutes with capabilities in delivering Deformable Mirrors to astronomers will be presented, as well as
lessons learned from the past 25 years of technological development and operation on sky. In conclusion, perspective
will be tentatively drawn for what regards the future of Deformable Mirror technology for Astronomy.

/pdf/overview-of-deformable-mirror-technologies-for-adaptive-j8uqtes2ke.pdf

Overview of deformable mirror technologies for adaptive optics and astronomy

The SAFARI instrument is a far-infrared imaging Fourier transform spectrometer for JAXA's SPICA mission. Taking advantage of the low emission of SPICA's 5 K telescope, SAFARI will provide sky background-limited, Nyquist-sampled spectroscopic imaging of a 2' × 2' field-of-view over 34-210 μm, creating significant new possibilities for far-infrared astronomy. SAFARI's aggressive science goals drive the development of a unique detector system combining large-format Transition Edge Sensor arrays and frequency division multiplexed SQUID readout with a high 160x multiplexing factor. The detectors and their cold readout electronics are packaged into 3 focal plane arrays that will be integrated into SAFARI's focal plane unit. Here we present the preliminary system design and current development status of the SAFARI detector system.

/pdf/the-spica-safari-detector-system-tes-detector-arrays-with-opodmoz6y8.pdf

The SPICA-SAFARI Detector System: TES Detector Arrays With Frequency-Division Multiplexed SQUID Readout

Subspace identification of circulant systems

SPIRE, the Spectral and Photometric Imaging Receiver, is a submillimetre camera and spectrometer for Herschel. It comprises a three-band camera operating at 250, 350 and 500 µm, and an imaging Fourier Transform Spectrometer covering 194-672 μm. The photometer field of view is 4x8 arcmin., viewed simultaneously in the three bands. The FTS has an approximately circular field of view of 2.6 arcmin. diameter and spectral resolution adjustable between 0.04 and 2 cm-1 ( λ/▵λ=20-1000 at 250 μm). Following successful testing in a dedicated facility designed to simulate the in-flight operational conditions, SPIRE has been integrated in the Herschel spacecraft and is now undergoing system-level testing prior to launch. The main design features of SPIRE are reviewed, the key results of instrument testing are outlined, and a summary of the predicted in-flight performance is given.

Herschel-SPIRE: Design, ground test results, and predicted performance - art. no. 701006

The E-ELT is a project led by the European Southern Observatory (ESO) for a 40-m class optical, near- and midinfrared,
ground-based telescope. When it will enter into operation, the E-ELT will be the largest and most powerful
optical telescope ever built. It will not only offer unrivalled light collecting power, but also exceedingly sharp images,
thanks to its ability to compensate for the adverse effect of atmospheric turbulence on image sharpness.
The basic optical solution for the EELT is a folded three-mirror anastigmat, using a 39-m segmented primary mirror
(M1), a 4-m convex secondary mirror (M2), and a 4-m concave tertiary mirror (M3), all active. Folding is provided by
two additional flat mirrors sending the beams to either Nasmyth foci along the elevation axis of the telescope. The
folding arrangement (flat M4 and M5 mirrors) is conceived to provide conveniently located flat surfaces for an adaptive
shell (M4) and field stabilization (M5).
That paper provides an overview of the specifications, design, and expected performance of the E-ELT optical systems.

https://www.eso.org/sci/libraries/SPIE2012/8444-69.pdf

E-ELT optomechanics: overview

A new prototype adaptive deformable mirror for future AO-systems is presented that consists of a thin continuous membrane on which push-pull actuators impose out-of-plane displacements. Each actuator has ±10?m stroke, nanometer resolution and only mW’s heat dissipation. The mirror’s modular design makes the mechanics, electronics and control system extendable towards large numbers of actuators. Models of the mirror are derived that are validated using influence and transfer function measurements. First results of a prototype with 427 actuators are also presented.

/pdf/validation-of-a-new-adaptive-deformable-mirror-concept-3ufre2qbze.pdf

Validation of a new adaptive deformable mirror concept

Future large optical telescopes require adaptive optics (AO) systems whose deformable mirrors (DM) have ever more degrees of freedom. This paper describes advances that are made in a project aimed to design a new AO system that is extendible to meet tomorrow's specifications. Advances on the mechanical design are reported in a companion paper [6272-75], whereas this paper discusses the controller design aspects. The numerical complexity of controller designs often used for AO scales with the fourth power in the diameter of the telescope's primary mirror. For future large telescopes this will undoubtedly become a critical aspect. This paper demonstrates the feasibility of solving this issue with a distributed controller design. A distributed framework will be introduced in which each actuator has a separate processor that can communicate with a few direct neighbors. First, the DM will be modeled and shown to be compatible with the framework. Then, adaptive turbulence models that fit the framework will be shown to adequately capture the spatio-temporal behavior of the atmospheric disturbance, constituting a first step towards a distributed optimal control. Finally, the wavefront reconstruction step is fitted into the distributed framework such that the computational complexity for each processor increases only linearly with the telescope diameter.

/pdf/distributed-control-in-adaptive-optics-deformable-mirror-and-476rgvcgai.pdf

Distributed control in adaptive optics: Deformable mirror and turbulence modeling

With the future growing size of telescopes, new, high-resolution, affordable wavefront corrector technology with low power dissipation is needed. A new adaptive deformable mirror concept is presented, to meet such requirements. The adaptive mirror consists of a thin (30-50 μm), highly reflective, deformable membrane. An actuator grid with thousands of actuators is designed which push and pull at the membrane’s surface, free from pinning and piston effects. The membrane and the actuator grid are supported by an optimized light and stiff honeycomb sandwich structure. This mechanically stable and thermally insensitive support structure provides a stiff reference plane for the actuators. The design is extendable up to several hundreds of mm's. Low-voltage electro-magnetic actuators have been designed. These highly linear actuators can provide a stroke of 15 micrometers. The design allows for a stroke difference between adjacent actuators larger than 1 micron. The actuator grid has a layer-based design; these layers extend over a large numbers of actuators. The current actuator design allows for actuator pitches of 3 mm or more. Actuation is free from play, friction and mechanical hysteresis and therefore has a high positioning resolution and is highly repeatable. The lowest mechanical resonance frequency is in the range of kHz so a high control bandwidth can be achieved. The power dissipation in the actuator grid is in the order of milliwatts per actuator. Because of this low power dissipation active cooling is not required. A first prototype is currently being developed. Prototypes will be developed with increasing number of actuators.

Large adaptive deformable membrane mirror with high actuator density

The mirror segments for the E-ELT and TLT are nearly equal in size and shape (hexagonal, 1.2 m over flat sides). They are very thin (about 50 mm) compared to their size. Supporting these mirrors and obtaining high optical performance is a challenge from design and manufacturing point of view. TNO has designed and build (together with VDL-ETG) three identical prototypes for supporting the mirror segments of the E-ELT. These mirror segments vary in size. Hence the gravity induced deformation of the mirror segments will vary from mirror to mirror segment when no measures are taken. The paper will concentrate on the design and analysis of the design features within the support structure to minimize the mirror deformation due to gravity. These features concern passive and active means to influence the mirror segment shape and to compensate for deformation differences.

/pdf/the-opto-mechanical-performance-prediction-of-thin-mirror-2zbe4o5h2t.pdf

The opto-mechanical performance prediction of thin mirror segments for E-ELT

The largest optical telescope in the world will be the E-ELT. Its primary mirror will be 42m in diameter. This mirror will consist of 984 hexagonal segments that are all individually supported. Each mirror will be controlled in six DOF while local shaping of the segments is provided by so called warping harnesses. These will correct for focus, astigmatism and trefoil. Hence a mirror with an extreme diameter to thickness ratio of almost 30 is obtained. Its support structure must guarantee a maximum surface form error of 30 nm rms independent of the segment attitude. Furthermore its stiffness to mass ratio must allow natural frequencies of 50Hz or higher to obtain sufficient bandwidth for the actuators that control the piston and tip/tilt of the segment. Designing such structure is a challenge that has been successfully completed. Three prototypes have been built and are about to be delivered to ESO. This paper discusses the main performance requirements and how they could be transferred into an elegant structure design. Furthermore an overview will be given on the main performance parameters in order to see whether the present design can be further optimized. © 2010 SPIE.

Roger Hamelinck

Papers

Validation of a new adaptive deformable mirror concept

Distributed control in adaptive optics: Deformable mirror and turbulence modeling

Large adaptive deformable membrane mirror with high actuator density

The opto-mechanical performance prediction of thin mirror segments for E-ELT

Meeting highest performance requirements for lowest price and mass for the M1 segment support unit for E-ELT