BLINC: A testbed for nulling interferometry in the thermal infrared

A key technology in NASA's plans for a Terrestrial Planet Finder (TPF) is nulling interferometry in the thermal infrared. This technique suppresses the overwhelming light from a star in order to study its immediate surroundings. To further develop nulling interferometry we have built the BracewelL Infrared Nulling Cryostat (BLINC). The instrument is designed to achieve high precision cancellation of an artificial source in the lab and of starlight on the telescope. Our goal is to achieve suppression of >10,000 both with a laser source and a broadband source over a 20% bandwidth. This is sufficient for ground-based observations with even short baseline interferometers since the finite diameter of the star does not allow suppression greater than that for most nearby sources. BLINC uses two parts of the MMT pupil to create an interferometer of 2.7 m diameter elements separated by 4 m. Active compensation for phase variations between the two apertures will be used to maintain the cancellation of the starlight in the presence of atmospheric turbulence. When combined with the adaptive secondary of the MMT to remove high order aberrations, BLINC will be able to achieve suppression of 10,000. This will allow detection of zodiacal dust around nearby stars as faint as 10 times the solar level and detection of companions large than 10 Jupiter masses for systems less than one billion years old. BLINC serves as a prototype for nulling with the Large Binocular Telescope which will be able to see zodiacal dust as faint as solar level and Jupiter mass or larger companions. Thus both in technological and scientific background BLINC will help begin the search for Earth-like planets.