Infrared Spatial Interferometer

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

The individual telescopes are movable and can be set up at different distances. In order to achieve the compact dimensions required for this, the mirror telescopes are so-called pound telescopes , in which a siderostat sits in front of a fixed, horizontally aligned parabolic mirror. The received signals are shifted into the HF frequency range by a heterodyne receiver and electronically combined with techniques from radio astronomical interferometers . The telescopes can be set up up to 70 m apart and thus achieve an angular resolution of 0.003 arc seconds at a wavelength of 11 µm .

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