Deformable mirrors

Thema:
Ground-based astronomy

Deformable Mirrors (DMs) are key components in Adaptive Optics (AO) systems employed in astronomy and laser communications to compensate for shape errors in optical elements and optical atmospheric disturbance, as well as for defense applications using high-powered lasers. Until now, deformable mirrors have suffered from inefficient and/or low-reliability actuators, with an inability to service system components. TNO has developed a Hybrid-Variable-Reluctance (HVR) DM technology which is reliable, serviceable, durable, scalable, modular, accurate, efficient and powerful.

Adaptive optics systems utilize optical signals, such as from laser guide stars, to measure atmospheric optical disturbance for ground-based telescopes. Deformable Mirrors (DMs) are used in a closed-loop with these signals to compensate for this disturbance for both astronomy and laser satellite communications, to correct the vision of the systems in real time and improve optical throughput. Within the context of space-based astronomical programs, AO systems are also key to achieving high-contrast imaging capabilities (e.g. exoplanet science) and compensate imperfections of the optics due to manufacturing flaws, misalignments, gravitational release and stress during launching and deploying phases.

Proving the principle

  • First deformable mirror TNO-HVR

    2017

    The first TNO-HVR DM was built for ESA around 2017, to prove the principle of use of adaptive optics in space for optical corrections. Since that time several laboratory DMs have been built and proven.

    First deformable mirror TNO-HVR
  • Adaptive secondary mirror for the NASA-IRTF telescope

    Early 2024

    In early 2024, TNO with its development partners listed below delivered an Adaptive Secondary Mirror (ASM) for the NASA-IRTF Telescope in Hawaii. The project went from design concept to delivered hardware in under a year, and the DM “closed the loop” in the first hour of operation on the telescope.

    TNO Adaptive Secondary Mirror
  • Adaptive secondary mirror for the UH88 telescope

    Late 2024

    In late 2024, TNO is planning to deliver an ASM for the UH88 (2.2 meter) telescope in Hawaii. This ASM is 620 mm in diameter and has 210 actuators. One of the key developments at this scale was developing a low-cost manufacturing method for accurate thin-shell glass mirrors, called heat-slumping or capture-range-replication, which can produce mirrors at a fraction of the cost of traditional grinding and polishing.

    Adaptive secondary mirror for the UH88 telescope

OFELIA Laser Communications Breadboard

Deformable Mirror DM2 used in OFELIA Laser Communications Breadboard – proved that beam-shaping (atmospheric pre-correction) can significantly improve signal quality through atmospheric turbulence.

Applications

Design studies have shown applicability for the following telescopes and applications:

  • European Solar Telescope (EST)
  • Keck Observatory
  • Gemini North Telescope
  • Thirty Meter Telescope
  • Automated Planet Finder
  • High Power Laser (HPL) for Defense

Keck concept_1

Conceptual Design of the KECK Adaptive Secondary Mirror, with ~3000 actuators, and a 1,4m diameter.

EST preliminary design

European Solar Telescope ASM, preliminary design (and breadboard): 2000 actuators; Ø0,8m,cooled optical surface.

Further (technical) details about deformable mirrors

TNO focusses on development, prototyping and performance testing. We have worked with the following development partners on the Hybrid-Variable-Reluctance (HVR) DMs:

  • University of Hawaii (US): advisor and launching customer
  • University of California (US): test and research partner, facesheet development
  • VDL (NL): actuators & support structure manufacturing
  • AAC Clyde Space (NL): electronics development
  • Fraunhofer (DE): facesheet pre-forming
  • NOVA (NL): facesheet finishing

To overcome drawbacks of existing DM technologies, TNO has developed systems with the following design features:

  • Patented Hybrid-Variable-Reluctance (HVR) actuators, with high linearity, high force and high efficiency for power and volume, and no need for active cooling in most applications
  • Highly reliable due to lack of wear/aging, redundant actuator windings and serviceable parts
  • Modular and scalable for various actuator counts, configurations and pitches in the range of 5 - 50 mm
  • Use of thicker mirror shells (2-4 mm) which are more durable and lower cost
  • Adaptable for space environment, including cryogenic

The key ingredient to TNO’s Hybrid-Variable-Reluctance (HVR) DM technology is the actuation principle, which generally has the following qualities:

  • Highly linear response (>99%), low hysteresis
  • High reliability: No wear/aging, compliancy, redundant windings
  • Low power dissipation (~ few mWatts per actuator)
  • Compact, low power electronics (PWM)
  • High force per volume; Scalable to large apertures, and actuator pitches (~40 times higher than a same size voice-coil)

HVR Actuator – Performance: Maximum force output ± 14N; Linear range of ±8N; 99.5% linearity; hysteresis <1%.

HVR Actuator – Performance: Maximum force output ± 14N; Linear range of ±8N; 99% linearity; hysteresis <1%.

HVR Actuator – stroke and force range

HVR Actuator – stroke and force range versus voice-coil and piezo actuators.

Latest HVR Actuator – DM16. Performance specs: Linear force range >30N PV; Displacement range >30µm PV- (up to 100µm PV, TBC); Internal resonance >2kHz; Efficiency; 60N/√W

Latest HVR Actuator – DM16. Performance specs: Linear force range >30N PV; Displacement range >30µm PV- (up to 100µm PV, TBC); Internal resonance >2kHz; Efficiency; 60N/√W.

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