We performed closed-loop lab testing of large-format deformable mirrors (DMs) with hybrid variable reluctance actuators. TNO has been developing the hybrid variable reluctance actuators in support for a new generation of adaptive secondary mirrors (ASMs), which aim to be more robust and reliable. Compared to the voice coil actuators, this new actuator technology has a higher current to force efficiency, and thus can support DMs with thicker facesheets. Before putting this new technology on-sky, it is necessary to understand how to control it and how it behaves in closed-loop. We performed closed-loop tests with the Shack-Hartmann wavefront sensor with three large-format deformable mirrors that use the TNO actuators: DM3, FLASH, and IRTF-ASM-1 ASM. The wavefront sensor and the real-time control systems were developed for the NASA Infrared Telescope Facility (IRTF) and the UH 2.2-meter telescope ASMs. We tested IRTF-ASM-1 on-sky and proved that it meets all of our performance requirements. This work presents our lab setup for the experiments, the techniques we have employed to drive these new ASMs, the results of our closed-loop lab tests for FLASH and IRTF-ASM-1, and the on-sky closed-loop results of IRTF-ASM-1 ASM.
We are developing an adaptive secondary mirror (ASM) that uses a new actuator technology created by the Netherlands Organization for Applied Scientific Research (TNO). The TNO hybrid variable reluctance actuators have more than an order of magnitude better efficiency over the traditional voice coil actuators that have been used on existing ASMs and show potential for improving the long-term robustness and reliability of ASMs. To demonstrate the performance, operations, and serviceability of TNO’s actuators in an observatory, we have developed a 36-actuator prototype ASM for the NASA Infrared Telescope Facility (IRTF) called IRTF-ASM-1. IRTF-ASM-1 provides the first on-sky demonstration of this approach and will help us evaluate the long-term performance and use of this technology in an astronomical facility environment. We present calibration and performance results with the ASM in a Meniscus Hindle Sphere lens setup as well as preliminary on-sky results on IRTF. IRTF-ASM-1 achieved stable closed-loop performance on-sky with H-band Strehl ratios of 35-40% in long-exposure images under a variety of seeing conditions.
TNO and partners at University of Hawai’i (UH), the NASA InfraRed Telescope Facility (IRTF), and the Center for Adaptive Optics (CfAO) at UCSC have been working on the realization of a 244 mm Adaptive Secondary Mirror (ASM) for the NASA IRTF called the IRTF-ASM-1. After successful performance testing of several laboratory prototypes, this project provided the first on-sky demonstration of TNO’s ASM technology at M2 location with an optically powered mirror shell.
The ASM is designed to retrofit the current passive M2. The ASM consists of a 244mm-diameter slumped convex aspherical mirror shell, manipulated by 36 hybrid variable reluctance actuators mounted on a light-weighted backing structure. The mirror shell is manufactured to the required accuracy at reduced cost through slumping by UCSC. The mirror shell is finished to final figure with Magnetorheological Finishing (MRF) by TNO before it was coated.
The ASM was shipped to UH in Hilo in February 2024, where performance was tested in the lab. The IRTF ASM saw ‘first light’ on telescope on the 23rd of April, already achieving stable closed-loop performance that was diffraction limited at the H-band (1.62 microns) with a long-exposure Strehl ratio of 35%-40% in sub-arcsecond seeing during the first night.
This paper will report on the status and first results of the IRTF ASM, including the latest status of the deformable mirror technology at TNO and an outlook to a second generation IRTF ASM with improved dynamic performance and increased actuator count.
Bart Snijders, Nagihan Sezgin, Fred Kampheus, Stefan Kuiper, Arjo Bos, Jan De Vreugd, Wouter Jonker, Mark Chun, Philip Hinz, Bert Dekker, Douwe Jan IJlst, Bart Venrooy, Wendy Kleijn, Robin Buuren, Matias Kidron, Esperanza Vielba Salcedo, Glenn Zalen, Stefan Zaal, Constantin Meiners, Rik Horst
This study presents the steps of manufacturing of thin shell mirrors for adaptive optics. TNO, in cooperation with the University of Hawaii Institute for Astrophysics, UC Santa Cruz, Fraunhofer IPT, NOVA and Huygens Optics, have been developing adaptive secondary mirrors (ASM) for the UH 2.2 meter and NASA IRTF telescopes. The ASM shells are slumped convex aspheres, with a 620 and 243 mm diameter respectively. The thin shell mirrors have fast actuators mounted on the backside to correct the wavefront errors caused by atmospheric turbulence. The manufacturing of thin shell mirror is the highlighted part of complete manufacturing steps of ASM for this study. This part includes anti-sticking coating for slumping, slumping, shape correction with grinding/polishing/MRF, and coating of front and backside of the mirror, as well as metrology. The manufacturing of the thin shells is one of the critical technologies for deformable mirrors for adaptive optics.
We report on progress at the University of Hawaii on the integration and testing setups for the adaptive secondary mirror (ASM) for the University of Hawaii 2.2-meter telescope on Maunakea, Hawaii. We report on the development of the handling fixtures and alignment tools we will use along with progress on the optical metrology tools we will use for the lab and on-sky testing of the system.
This paper describes the preliminary design of the Adaptive Secondary Mirror (ASM) for the European Solar Telescope (EST), as designed by TNO. This ASM will contain 1950 actuators over an optical aperture of Ø80cm. The mirror-shell of this ASM is concave with a radius of 2.156m and has a thickness of 2.5mm. To cope with the high optical heat-load, the mirror shell will be cooled actively by means of conduction through a small (0.3mm) airgap between the mirror shell and the cooled SiC supporting structure. One of the unique characteristics of this ASM are the highly efficient actuators by TNO, delivering 30N Peak-to-Valley of linear force range within a packaging of Ø15x40mm. These actuators are based on the proven electromagnetic actuation principle by TNO but have been significantly redesigned to improve manufacturability and integration. The actuators are interfaced to the mirror shell via a stiff carbon fiber strut assembly and are designed to be replaceable during off-telescope maintenance. For overall alignment of the ASM a hexapod is used, while a faster tip-tilt stage is used to compensate for tip-tilt disturbances up to 20Hz bandwidth. The optical performance of the ASM under various environmental conditions has been extensively studied with Finite-Element-Analysis. To verify the performances of the actuator and the cooling systems, an actuator and thermal- breadboard are being constructed.
Adaptive optics is an advanced technique developed for large telescopes. It turns out to be challenging for smaller telescopes (0.5~2m) due to the small isoplanatic angle, small subapertures and high correction speeds needed at visible wavelengths, requiring bright stars for guiding, severely limiting the sky coverage. The motivation to develop compact and robust AO system for small telescopes is two-fold: On the one hand, schools and universities often have access to small telescopes as part of their education programs. Also, researchers in countries with fewer resources could also benefit from well-engineered and reliable adaptive optics on smaller telescopes for research and education purposes. On the other hand, amateur astronomers and enthusiasts want improved image quality for visual observation and astrophotography. Implementing readily accessible adaptive optics in astronomy clubs would also likely have a significant impact on citizen science.
Conventionally, facesheets for deformable mirrors (DM) are manufactured through grinding, polishing and finishing of a piece of optical glass. Due to the amount of material that needs to be removed, the required surface form errors and the complex handling of the fragile product throughout all manufacturing steps, this is a lengthy, risky and expensive process. For the 620mm-diameter adaptive secondary mirror (ASM) of the University of Hawaii’s 2.2-meter telescope, we develop an alternative process where the facesheet is manufactured by hot forming (‘slumping’) of a flat glass pre-form in a mold directly to the proper shape. Since low-spatial surface form errors can be corrected with the DM actuators to a large extent, only the mid/high-spatial errors beyond the period of the actuator spacing are considered critical. Through accurate modeling, and an iterative approach of hot-forming, metrology and adjustment of process parameters, the forming process is optimized to obtain the near-final shape. This approach limits the amount of required finishing operations, resulting in a facesheet meeting specifications at significantly reduced cost. We present results for the modeling & simulations, and the progress in manufacturing of this ASM facesheet.
A consortium of industrial and academic partners, coordinated by TNO, is working on the realization of a 620mm adaptive secondary mirror (ASM) for the University of Hawaii’s 2.2-meter telescope [1][2][3]. The ASM consists of a 620mm-diameter slumped convex aspherical mirror shell, manipulated by 210 variable-reluctance actuators mounted on a light-weighted support frame. The mirror shell is manufactured to the required accuracy at low cost through slumping. The actuators are driven by dedicated PWM current drivers and commanded through a real-time FPGA-based interface. After successful performance testing of several laboratory prototypes[4], this project will provide the definitive on-sky demonstration of this new technology. We report on the manufacturing and testing of the major subsystems, and on the integration status of the ASM as a whole.
We describe the current plans for developing an adaptive secondary mirror-based (ASM) adaptive optics (AO) system for WMKO. An ASM allows for the integration of AO into the telescope itself, broadening use of AO to include wide-field enhanced seeing, high contrast observations, and enabling future multi-conjugate upgrades. Such a system has the potential for enhancing a range of science objectives, improving the performance of both existing and future instrumentation at Keck. We describe a system level ASM-AO concept based on hybrid variable reluctance actuators, developed by TNO that simplifies the implementation of ASM’s.
Advancements in high-efficiency variable reluctance actuators are an enabling technology for building the next generation of large-format deformable mirrors, including adaptive secondary mirrors. The Netherlands Organization for Applied Scientific Research (TNO) has developed a new style of hybrid variable-reluctance actuator that requires approximately seventy-five times less power to operate as compared to the traditional style of voice-coil actuators. We present the initial performance results from laboratory testing of TNO's latest 19-actuator prototype mirror, FLASH. We report the linearity, hysteresis, natural shape flattening, actuator cross-coupling, creep, and repeatability of the FLASH prototype and compare the results to previous TNO prototype deformable mirrors. We also present results of the performance of FLASH on sub-millisecond timescales in order to estimate the limits for the use of this technology when utilized to perform high-contrast imaging adaptive optics.
Advancements in making high-efficiency actuators are an enabling technology for building the next generation of large-format deformable mirrors. The Netherlands Organization for Applied Scientific Research (TNO) has developed a new style of variable-reluctance actuator that requires approximately eighty times less power to operate as compared to the traditional style of voice-coil actuators. We present the performance results from laboratory testing of TNO's 57-actuator large-format deformable mirror from measuring the influence functions, linearity, hysteresis, natural shape flattening, actuator cross-coupling, creep, repeatability, and actuator lifetime. We measure a linearity of 99.4 ± 0.33% and hysteresis of 2.10 ± 0.23% over a stroke of 10 microns, indicating that this technology has strong potential for use in on-sky adaptive secondary mirrors (ASMs). We summarize plans for future lab prototypes and ASMs that will further demonstrate this technology.
TNO and industrial partners are developing a new type of adaptive secondary mirrors (ASM) for the University of Hawaii 2.2-meter telescope, consisting of 210 actuators, in an overall volume of ø63cm by 15cm height, and having an aspherical convex mirror-shell of 3,5mm thickness. The novel actuator technology enables a compact system without active cooling that can be retro-fitted within the same mass and volume of an existing passive secondary mirror. This development enables affordable and reliable ASM systems for the world’s larger telescopes as well as the many telescopes in the 2-4 meter class. This paper presents the overall design of this ASM and focusses on the performance analysis regarding its figure quality, its dynamical behavior and the related closed loop performances.
An Adaptive secondary mirror (ASM) allows for the integration of adaptive optics (AO) into the telescope itself. Adaptive secondary mirrors, based on hybrid variable reluctance (HVR) actuator technology, developed by TNO, provide a promising path to telescope-integrated AO. HVR actuators have the advantage of allowing mirrors that are sti↵er, more power ecient, and potentially less complex than similar, voice-coil based ASM’s. We are exploring the application of this technology via a laboratory testbed that will validate the technical approach. In parallel, we are developing conceptual designs for ASMs at several telescopes including the Automated Planet Finder Telescope (APF) and for Keck Observatory. An ASM for APF has the potential to double the light through the slit for radial velocity measurements, and dramatically improved the image stability. An ASM for WMKO enables ground layer AO correction and lower background infrared AO observations, and provides for more flexible deployment of instruments via the ability to adjust the location of the Cassegrain focus.
We are developing a new adaptive secondary mirror (ASM) for the University of Hawaii 2.2-meter telescope based on a novel and very efficient hybrid variable reluctance actuator developed by TNO. The actuator technology has broad implications on the ASM design and results in an ASM with a thicker facesheet, lower power dissipation, and simple controls. We report here preparations and plans for lab testing as well as on-sky demonstration of the ASM. The lab calibrations of the ASM influence functions will use a phase measuring deflectometry setup. The on-sky tests will include the evaluation of the use of the ASM for narrow field AO observations at visible through near infrared wavelengths, for very wide fields of view ground-layer adaptive optics, and for seeing limited non-adaptive optics observations.
An adaptive secondary mirror (ASM) is currently being developed for the UH2.2 telescope, consisting of a slumped 620mm convex aspherical facesheet, manipulated by 210 variable-reluctance actuators and supported on a silicon aluminium alloy support structure. The total power dissipation of the actuators is expected to be under 3 Watts. The ASM will weigh around 55kg, which is about 15kg lighter than the original passive secondary mirror (M2). We present the design, breadboarding activities and manufacturing status of this adaptive mirror. The project is on track for delivery of the ASM in Hawaii in the middle of 2021.
This paper presents the first test results of a novel Fine Steering Mirror (FSM) for optical communication terminals. The FSM utilizes efficient variable reluctance actuators, tailored for the specific application, making it highly compact and power efficient. The test results demonstrate a high dynamical performance of <1.7kHz closed-loop bandwidth, and an optical angular range of more than ±2° in two axes. The actual optical angular jitter is less than 1.5 μrad. These numbers demonstrate that this FSM is highly suitable for the evolving field of inter-satellite laser communications.
Optical communications will complement radio frequency (RF) communications in the coming decades to enhance throughput, power efficiency and link security of satellite communication links. To enable optical communications technology for intersatellite links and (bi-directional) ground to satellite links, TNO develops a suite of technologies in collaboration with industry, which comprises of terminals with different aperture sizes, coarse pointing assemblies and fast steering mirrors. This paper presents the current state of the development of TNO technology for optical space communications. It mainly focuses on the development of an optical head with an entrance aperture of 70 mm, an optical bench for CubeSats and coarse pointing assemblies (CPAs). By continuing these steps, world wide web based on satellite communications will come closer.
TNO is developing a novel Large Dynamic Range Atomic Force Microscope (LDR-AFM), primarily but not exclusively designed for sub-nm accurate overlay metrology. The LDR-AFM combines an AFM with a 6 degrees- of-freedom interferometric positioning stage, thereby enabling measurements of sub-nm features on a wafer over multiple millimeters marker-to-feature distances. The current work provides an overview of recent developments and presents the first results obtained after final integration of the complete system. This includes results on the AFM head development, the validated positioning stage performance, the first AFM images, and long-term stability measurements.
Optical communications will complement radio frequency (RF) communications in the coming decades to enhance throughput, power efficiency and link security of satellite communication links. To enable optical communications technology for intersatellite links and (bi-directional) ground to satellite links, TNO develops a suite of technologies in collaboration with industry. Throughout these developments there is a particular aim for high levels of system integration, compactness and low recurring cost in order to meet the overall requirements related to market viability. TNO develops terminals with aperture sizes of 70 and 17 mm, coarse pointing assemblies and fast steering mirrors. This paper discusses the state of development of these different technologies and provides and outlook towards the future.
TNO is developing Deformable Mirror (DM) technology, targeted for aberration correction in high-end Adaptive Optics (AO) applications in the field of lithography, astronomy, space and laser communication. The heart of this deformable mirror technology is a unique actuator technology based on the variable reluctance principle. The main advantages of this technology are the inherent high reliability, linearity (>99%), and high efficiency in terms of force per volume and unit power. Based on this actuator technology TNO built and tested a prototype DM, with 57 actuators, and a mirror diameter of Ø160mm. The test results show a highly linear actuator response, with less than 1% hysteresis over a stroke of 40μm. Atmospheric aberration correction has been shown with these DM’s in a free space laser-communication bread board. The same actuator technology is also used in the application of a highly compact Fine Steering Mirror (FSM), with an overall volume of Ø27x30mm, with a Ø20mm mirror. This FSM is targeted for satellite-based laser-communication terminals. Furthermore, a design study has been carried out to show the scalability of this technology towards large (~Ø1m to ~Ø3m) adaptive (secondary) mirrors with several hundreds, up to thousands of actuators. In this paper these different DM and FSM’s are discussed, and the latest test results obtained with the DM prototypes are presented.
TNO and DLR envision optical free-space communication between ground stations and geostationary telecommunication satellites to replace the traditional RF links for the next generation of Very High Throughput Satellites. To mitigate atmospheric turbulence, an Adaptive Optics (AO) system will be used. TNO and DLR are developing breadboards to validate Terabit/s communication links using an AO system. In this paper the breadboard activities and first results of the sub-systems will be presented. Performance of these subsystems will be evaluated for viability of terabit/s optical feeder links.
To increase the collecting power and to improve the angular imaging resolution, space telescopes are evolving towards larger primary mirrors. The aerial density of the telescope mirrors needs to be kept low, however, to be compatible with the launch requirements. A light-weight (primary) mirror will introduce additional optical aberrations to the system. These may be caused by for instance manufacturing errors, gravity release and thermo-elastic effects. Active Optics (AO) is a key candidate technology to correct for the resultant wave front aberrations [1].
Stefan Kuiper, Niek Doelman, Evert Nieuwkoop, Ton Overtoom, Tjeerd Russchenberg, Martijn van Riel, Justin Wildschut, Max Baeten, Jet Human, Helma Spruit, Sanneke Brinkers, Matthew Maniscalco
Over the last decade TNO has developed a deformable mirror concept using electromagnetic actuators with the main advantages of having very low non-linearity and hysteresis, low power consumption, and high inherent reliability of the actuators. TNO recently started a program to redesign the electromagnetic actuator to improve the actuator efficiency, allowing higher actuator force per volume and per wattage. The increased actuator efficiency gives improvement of the DM performance in terms of dynamical performance, actuation range, and power dissipation. With this technology various applications in the fields of ground-based astronomy and space missions are targeted.
Stefan Kuiper, Erik Fritz, Will Crowcombe, Thomas Liebig, Geerten Kramer, Gert Witvoet, Tom Duivenvoorde, Ton Overtoom, Ramon Rijnbeek, Erwin van Zwet, Anton van Dijsseldonk, Arie den Boef, Marcel Beems, Leon Levasier
Nowadays most overlay metrology tools assess the overlay performance based on marker features which are deposited next to the functional device features within each layer of the semiconductor device. However, correct overlay of the relatively coarse marker features does not directly guarantee correct overlay of the much smaller device features. This paper presents the development of a tool that allows to measure the relative distance between the marker and device features within each layer of the semiconductor device, which can be used to improve the overlay at device feature level. In order to be effective, the marker to device feature distance should be measured with sub-nanometer measurement uncertainty over several millimeters range. Furthermore, the tool should be capable of profiling the marker features to allows prediction of the location interpretation of the optical diffraction based alignment sensors, which are sensitive for potential asymmetry of the marker features.
To enable this, a highly stable Atomic Force Microscope system is being developed. The probe is positioned relative to the wafer with a 6DOF controlled hexapod stage, which has a relatively large positioning range of 8x8mm. The position and orientation of this stage is measured relative to the wafer using 6 interferometers via a highly stable metrology frame. A tilted probe concept is utilized to allow profiling of the high aspect ratio marker and device features. Current activities are aimed at demonstrating the measurement capabilities of the developed AFM system.
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