Technology development for space based Vortex Coronagraphy

As demonstrated recently at the Palomar Observatory, the Optical Vortex Coronagraph (OVC) can enable high-contrast imaging observations very near bright stars. A small-angle observational capability is especially important because it can reduce the telescope diameter needed for close companion observations. However, as the OVC is a fairly new technique, the vortex phase masks needed to enable the very high contrast imaging required to detect terrestrial exoplanets (~ 10^-10 relative to the host star) are not yet in hand. This paper thus first briefly describes the basic operation of the vortex coronagraph, and then turns to a discussion of a promising method of manufacturing the needed vortex masks. In particular, vortex phase masks based on circularly-symmetric half-wave plates made of liquid-crystal polymers have already achieved very good performance. The practical limitations of such masks, and the means of overcoming these limitations are also addressed. Successful development of the requisite vortex masks could potentially enable a range of high-contrast coronagraphic space missions, from an initial explorer class mission to a large flagship class exoplanet imaging mission.