Astronomical demonstration of an optical vortex coronagraph

The optical vortex coronagraph (OVC) provides an elegant solution for putting off the Airy disk image of the star by taking advantage of the unique diffraction properties of an optical vortex lens or subwavelength diffraction grating. A vortex lens using electron beam lithography was fabricated, and the optical system was designed using achromatic doublet lenses. The image of the star was made stationary by using a feedback system composed of a piezoelectrically controlled tip-tilt mirror and a fast camera. The telescope was directed at the binary star system, Cor Caroli, with and without the vortex lens in place. Exposure time was 300s and dark frame subtraction was used. It was observed that improvements in the quality of the vortex lens and better correction for higher order aberrations may allow the OVC to reach contrasts that are suitable for a space telescope mission.