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

TNO, together with its partners Micromega and SRON, have designed a cryogenic scanning mechanism for use in the SAFARI Fourier Transform Spectrometer (FTS) on board of the SPICA mission. The optics of the FTS scanning mechanism (FTSM) consists of two back-to-back cat's-eyes. The optics are mounted on a central "back-bone" tube which houses all the important mechatronic parts: the magnetic bearing linear guiding system, a magnetic linear motor serving as the OPD actuator, internal metrology with nanometer resolution, and a launch lock. A magnetic bearing is employed to enable a large scanning stroke in a small volume. It supports the optics in a freefloating way with no friction, or other non-linearities, enabling sub-nanometer accuracy within a single stage with a stroke of -4 mm to +31.5 mm. Because the FTSM will be used at cryogenic temperatures of 4 Kelvin, the main structure and optics are all constructed from 6061 Aluminum. The overall outside dimensions of the FTSM are: 393 × 130 × 125 mm, and the mass is 2.2 kg. © 2010 SPIE.

/pdf/cryogenic-magnetic-bearing-scanning-mechanism-design-for-the-2vpzhkpaw7.pdf

Cryogenic magnetic bearing scanning mechanism design for the SPICA/SAFARI Fourier transform spectrometer

The first prototype of an actuator for a new adaptive deformable mirror (DM) is presented together with the development of a 61-actuator grid element. The DM design consists of a thin membrane which acts as the correcting element. A grid of low voltage electro-magnetic push-pull actuators, impose out-of-plane displacements in the mirror's membrane. To provide a stable and stiff reference plane for the actuators, a mechanically stable and thermally decoupled honeycomb support structure is added. Several variants of variable reluctance actuators are considered. Each actuator consists of a closed magnetic circuit in which a strong permanent magnet (PM) provides a static magnetic force attracting ferromagnetic material. By applying a current through a coil which is situated around this magnet, this force can be influenced. Depending on the mechanical stiffness of the actuator, this leads to a certain displacement. Both the PM and the coil are connected to the fixed world and only the ferromagnetic material will move. The actuators are produced in arrays which make the design easy and extendable. 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. The paper describes how the actuator stiffness and efficiency can be controlled. A test-setup is developed in which the actuator characteristics are measured.

/pdf/large-adaptive-deformable-mirror-design-and-first-prototypes-9tx97fx27j.pdf

Large adaptive deformable mirror: design and first prototypes

In the design of a large adaptive deformable membrane mirror, variable reluctance actuators are used. These consist of a closed magnetic circuit in which a strong permanent magnet provides a static magnetic force on a ferromagnetic core which is suspended in a membrane. By applying a current through the coil which is situated around the magnet, this force is influenced, providing movement of the ferromagnetic core. This movement is transferred via a rod imposing the out-ofplane displacements in the reflective deformable membrane. In the actuator design a match is made between the negative stiffness of the magnet and the positive stiffness of the membrane suspension. If the locality of the influence functions, mirror modes as well as force and power dissipation are taken into account, a resonance frequency of 1500 Hz and an overall stiffness of 1000 N/m for the actuators is needed. The actuators are fabricated and the dynamic response tested in a dedicated setup. The Bode diagram shows a first eigenfrequency of 950 Hz. This is due to a lower magnetic force than expected. A Helmholtz coil setup was designed to measure the differences in a large set of permanent magnets. With the same setup the 2nd quadrant of the B-H curve is reconstructed by stacking of the magnets and using the demagnetization factor. It is shown that the values for Hc and Br of the magnets are indeed lower than the values used for the initial design. New actuators, with increased magnet thickness, are designed and currently fabricated.

/pdf/actuator-tests-for-a-large-deformable-membrane-mirror-4ue0u3tapb.pdf

Actuator tests for a large deformable membrane mirror

A large adaptive deformable mirror with high actuator density is presented The DM consists of a thin continuous membrane which acts as the correcting element A grid of low voltage electro-magnetical push-pull actuators, - located in an actuator plate -, impose out-of-plane displacements in the mirror's membrane To provide a stable and stiff reference plane for the actuators, a mechanically stable and thermally decoupled honeycomb support structure is added The design is suited for mirrors up to several hundred mm with an actuator pitch of a few mm One of the key elements in the design is the actuator grid Each actuator consists of a closed magnetic circuit in which a strong permanent magnet (PM) attracts a ferromagnetic core Movement of this core is provided by a low stiffness elastic guiding A coil surrounds the PM Both the coil and the PM are connected to the fixed world By applying a current through the coil, the magnetic force acting on the core can be influenced This force variation will lead to translation of the ferromagnetic core This movement is transferred to the reflective mirror surface in a piston-free manner The design allows for a long total stroke and a large inter actuator stroke The actuators are produced in arrays which make the design modular and easily extendable The first actuators and an actuator grid are produced and tested in a dedicated test set-up This paper describes how relevant actuator properties, such as stiffness and efficiency, can be influenced by the design The power dissipation in the actuator grid is optimized to a few milliwatts per actuator, thereby avoiding active cooling

https://pure.tue.nl/ws/files/1765510/600502084999238.pdf

Large adaptive deformable membrane mirror with high actuator density: design and first prototypes

TNO, together with its partners, have designed a cryogenic scanning mechanism for use in the SAFARI Fourier Transform Spectrometer (FTS) on board of the SPICA mission. SPICA is one of the M-class missions competing to be launched in ESA's Cosmic Vision Programme in 2022. JAXA leads the development of the SPICA satellite and SRON is the prime investigator of the Safari instrument. The FTS scanning mechanism (FTSM) has to meet a 35 mm stroke requirement with an Optical Path Difference resolution of less then 15 nm and must fit in a small volume. It consists of two back-to-back roof-top mirrors mounted on a small carriage, which is moved using a magnetic bearing linear guiding system in combination with a magnetic linear motor serving as the OPD actuator. The FTSM will be used at cryogenic temperatures of 4 Kelvin inducing challenging requirements on the thermal power dissipation and heat leak. The magnetic bearing enables movements over a scanning stroke of 35.5 mm in a small volume. It supports the optics in a free-floating way with no friction, or other non-linearities, with sub-nanometer accuracy. This solution is based on the design of the breadboard ODL (Optical Delay Line) developed for the ESA Darwin mission and the MABE mechanism developed by Micromega Dynamics. During the last couple of years the initial design of the SAFARI instrument, as described in an earlier SPIE 2010 paper, was adapted by the SAFARI team in an evolutionary way to meet the changing requirements of the SPICA payload module. This presentation will focus on the evolution of the FTSM to meet these changing requirements. This work is supported by the Netherlands Space Office (NSO). © 2012 SPIE.

/pdf/spica-safari-fourier-transform-spectrometer-mechanism-3evcmhro5i.pdf

Roger Hamelinck

Papers

Cryogenic magnetic bearing scanning mechanism design for the SPICA/SAFARI Fourier transform spectrometer

Large adaptive deformable mirror: design and first prototypes

Actuator tests for a large deformable membrane mirror

Large adaptive deformable membrane mirror with high actuator density: design and first prototypes

SPICA/SAFARI Fourier transform spectrometer mechanism evolutionary design