Single Aperture Imaging Astrometry with a Diffracting Pupil: Laboratory demonstration
Eduardo Bendek, Mark Ammons, Thomas Milster, Olivier Guyon
University of Arizona
A laboratory is being set up at university of Arizona to serve as proof of concept of a novel technique to overcome the astrometric errors caused by optical distortions on imaging telescopes. This new technique enables sub microarcsecond astrometry with medium-size (<2-m) space telescopes, and can be used simultaneously with coronagraphy for exhaustive characterization of exoplanets (mass, spectra, orbit). The technique uses an array of 10 μm dots over the primary mirror causing diffraction spikes on the image due the polychromatic nature of the source. The spikes are used as reference for the astrometry measurements and encode any aberration of the optical system. The laboratory aims to achieve 10 μas, simulating 0.14 uas precision on a 1.4 m telescope. Prototype mirrors with the small diffractive dots have been manufactured by lithography. We describe the laboratory test design and data analysis. We also show early results obtained with the diffractive mirror, showing the diffraction spikes which calibrate distortions in the optical system. Technical challenges to apply this technique to a full size optical system with an aspheric primary mirror are discussed.