Infrared Spatial Interferometer

The Infrared Spatial Interferometer (ISI ) is an imaging interferometer for astronomical observation, which consists of three coupled 1.65 -meter diameter mirror telescopes. It is located at the Mount Wilson Observatory and was developed by the Space Sciences Lab, University of California, Berkeley under the direction of Charles Townes. It is adapted for observing the mid-infrared wavelength range. After many years of operation with two telescopes were on 9 July 2003 for the first time three telescopes as an interferometer in operation.

The individual telescopes are movable and can be positioned at different distances. In order to achieve the necessary compact size, reflecting telescopes are called pound telescopes, with which a Siderostat sitting in front of a fixed horizontally aligned parabolic mirror. The received signals are shifted by a superheterodyne receiver in the RF frequency range and electronically combined with techniques from radio astronomy interferometers. Telescopes up to 70 m are placed away from each other, and thus achieve an angular resolution of 0.003 seconds of arc at a wavelength of 11 microns.