Active optics and force optimization for the first 8.4-m LBT mirror

Martin, Hubert M.; Cuerden, Brian; Dettmann, Lee R.; Hill, John M.

doi:10.1117/12.550464

Cited by 24 publications

(9 citation statements)

References 8 publications

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“…Ground-based applications of active or adaptive optics on slower time scales include correcting gravitational sag, differential flexture, and thermal drift. 58,59 We are especially looking forward to studying the PMADM's response to the laboratory laser heating test, which will provide demagnetization and focus adjustment without translation of the drive magnet. Since photoactuation requires heating to achieve demagnetization, thermal relaxations times for these actuators are expected to be relatively slow (∼1 Hz) (Li et al).…”

Section: Summary and Future Workmentioning

confidence: 99%

Demonstration of magnetic and light-controlled actuation of a photomagnetically actuated deformable mirror for wavefront control

et al. 2021

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Deformable mirrors (DMs) have wide applications ranging from astronomical imaging to laser communications and vision science. However, they often require bulky multichannel cables for delivering high power to their drive actuators. A low-powered DM, which is driven in a contactless fashion, could provide a possible alternative to this problem. We present a photomagnetically actuated deformable mirror (PMADM) concept, which is actuated in a contactless fashion by a permanent magnet and low-power laser heating source. We present the laboratory demonstration of prototype optical surface quality, magnetic control of focus, and COMSOL simulations of its precise photocontrol. The PMADM prototype is made of a magnetic composite (polydimethylsiloxane + ferromagnetic CrO 2 ) and an optical-quality substrate layer and is 30.48 mm × 30.48 mm × 175 μm in dimension with an optical pupil diameter of 8 mm. It deforms to 5.76 μm when subjected to a 0.12-T magnetic flux density and relaxes to 3.76 μm when illuminated by a 50-mW laser. A maximum stroke of 8.78 μm before failure is also estimated considering a 3× safety factor. Our work also includes simulation of astigmatism generation with the PMADM, a first step in demonstrating control of higher order modes. A fully developed PMADM may have potential application for wavefront corrections in vacuum and space environments.

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Section: Summary and Future Workmentioning

confidence: 99%

Demonstration of magnetic and light-controlled actuation of a photomagnetically actuated deformable mirror for wavefront control

et al. 2021

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“…A modal correction is applied, using a limited number of bending modes, or combinations of the individual actuator forces, to alter the shape of the mirror surface. [1][2][3][4] The bending modes are ordered from low to high spatial frequency correction. Using more bending modes reduces the residual surface error but increases the range of actuator forces.…”

Section: Introductionmentioning

confidence: 99%

Analysis of active optics correction for a large honeycomb mirror

Blomquist,

Martin,

Kang

et al. 2023

Astronomical Optics: Design, Manufacture, and Test of Space and Ground Systems IV

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In the development of space-based large telescope systems, having the capability to perform active optics correction allows correcting wavefront aberrations caused by thermal perturbations so as to achieve diffraction-limited performance with relaxed stability requirements. We present a method of active optics correction used for current ground-based telescopes and simulate its effectiveness for a large honeycomb primary mirror in space. We use a finite-element model of the telescope to predict misalignments of the optics and primary mirror surface errors due to thermal gradients. These predicted surface error data are plugged into a Zemax ray trace analysis to produce wavefront error maps at the image plane. For our analysis, we assume that tilt, focus and coma in the wavefront error are corrected by adjusting the pointing of the telescope and moving the secondary mirror. Remaining mid- to high-order errors are corrected through physically bending the primary mirror with actuators. The influences of individual actuators are combined to form bending modes that increase in stiffness from low-order to high-order correction. The number of modes used is a variable that determines the accuracy of correction and magnitude of forces. We explore the degree of correction that can be made within limits on actuator force capacity and stress in the mirror. While remaining within these physical limits, we are able to demonstrate sub-25 nm RMS surface error over 30 hours of simulated data. The results from this simulation will be part of an end-to-end simulation of telescope optical performance that includes dynamic perturbations, wavefront sensing, and active control of alignment and mirror shape with realistic actuator performance.

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“…For example, in our previous work, we proposed a combined process of small ball-end contact polishing and magnetorheological polishing for small aspherical molds, which can reduce the SR from Ra 8.5972 nm to Ra 1.2694 nm [ 10 ]. H. M. Martin et al [ 13 ] used stress disk polishing technology to suppress mid-high frequency errors, and polished the primary mirror of an 8.4 m LBT telescope to a surface accuracy of RMS 18 nm. DeGroote Nelson et al [ 14 ] used a high-frequency vibration method with full aperture coverage, which can also suppress HFE well.…”

Section: Introductionmentioning

confidence: 99%

Surface Quality Control Strategy of Aspherical Mold Based on Screw Feed Polishing of Small Polishing Tool

et al. 2022

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For small aspherical molds, it is difficult for the existing polishing method to take into account the correction of the surface error and the control of the uniformity of the surface roughness (SR) distribution, because the polishing tool is always larger than the small mold. Therefore, we used viscoelastic polyester fiber cloth to wrap the small steel ball as a polishing tool to adapt to the surface shape change of the aspherical mold, and designed a semi-flexible small polishing disc tool with microstructure, which can better adapt to the curvature change of aspherical surface and obtain better SR Ra. At the same time, a combined polishing method of constant speed and variable speed for screw feed was proposed to improve the uniformity of SR distribution in the paper. Then, a series of theoretical analysis and experimental verification were carried out in this paper to predict the tool influence function (TIF) of the two polishing tools and the effectiveness of the combined polishing method. In the experiment, a TIF bandwidth of about 0.46 mm was obtained with a small spherical polishing tool, which favors the surface shape correction of the small aspherical mold. The experiment of uniform removal with a small polishing disc tool was carried out to quickly reduce the Ra. Finally, the surface quality of the aspherical mold was effectively improved, combined with the constant speed and variable speed polishing modes of screw feed of the small spherical polishing tool and the smoothing effect of the small polishing disc tool. The peak valley (PV) of two small aspherical molds with an optical effective diameter less than 13 mm converged from 0.3572 μm and 0.2075 μm to 0.1282 μm and 0.071 μm, respectively. At the same time, the SR dispersion coefficient was reduced from 27.9% and 41.6% to 14.2% and 12.7%, respectively. The study provides a good solution for the surface quality control of small aspherical molds.

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Active optics and force optimization for the first 8.4-m LBT mirror

Cited by 24 publications

References 8 publications

Demonstration of magnetic and light-controlled actuation of a photomagnetically actuated deformable mirror for wavefront control

Demonstration of magnetic and light-controlled actuation of a photomagnetically actuated deformable mirror for wavefront control

Analysis of active optics correction for a large honeycomb mirror

Surface Quality Control Strategy of Aspherical Mold Based on Screw Feed Polishing of Small Polishing Tool

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