Developing Low-Cost Adaptive Optics Telescopes for Long Baseline Optical Interferometry
Abstract
Our research examines the use of adaptive optics (AO) in tandem with low-quality optics to determine if diffraction limited results can be achieved using active corrective optics. The 1μm scale of wavefront corrections provided by AO systems are substantially greater than the ~50nm construction specifications of typical telescopes. Thus, this pairing of optics and software could increase image quality while decreasing cost by significantly (~20x) relaxing mechanical requirements. As a baseline, we measured a 6in lab-quality flat with a Zygo interferometer, an instrument built for surface inspection of diffraction-limited optics. To contrast this result, we similarly inspected a low-quality mirror. We found roughly 2 full waves, about 1μm, of smoothly varying static wavefront distortion across the ~5in Zygo inspection aperture. Our lab setup consisted of a Thorlabs AO Kit (model 7) with light source, deformable mirror (DM), and Shack-Hartman wavefront sensor (WFS). A 2.5cm beam expanded from a 0.34mW laser diode hit the low-quality mirror, which retroreflected into the AO system and was re-collimated to 5mm to match the sensor diameter of the WFS. Fifteen data sets were collected to find the Peak-to-Valley (PV) and root-mean-square (rms) of the wavefront measured from the low-quality mirror and the reconstructed wavefront corrected by the DM. This second data set was used to calculate the difference between the measured and reconstructed wavefronts. The process was repeated by replacing the low-quality mirror with a lab-quality mirror rated to λ/20. The PV measurement for the low-quality mirror was 55μm with a rms of 12.7μm, compared to the lab-quality mirror whose PV was 53μm with a rms of 10.8μm. The difference between the low-quality mirror's wavefront and the DM reconstructed wavefront was a PV of 0.21μm with a rms of 0.04μm. The resultant wavefront corrected 80% past it's predicted outcome of 1μm. Our results indicate it would be advantageous to use a telescope design that assumes integral AO from the outset; further benefits come from tailoring the telescopes to the narrow set of specifications that emphasize use in a narrow-angle long-baseline optical interferometry system.
- Publication:
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American Astronomical Society Meeting Abstracts #233
- Pub Date:
- January 2019
- Bibcode:
- 2019AAS...23346207H