AAS 197, January 2001
Session 15. Optical and IR: Small Telescopes, Instrumentation and Processing
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

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[15.08] A Comparison of Michelson and Fizeau Beam Combiners for Optical Interferometry

M. L. Cobb (Southeast Missouri State University)

There are two different, broad categories of beam combiners in optical interferometry. The pupil plane beam combiner is referred to as a Michelson combiner in recognition of the work by Michelson and Pease. The image plane beam combiner is referred to as a Fizeau combiner after the work of Armand Fizeau.

This poster will contrast the advantages and disadvantages of the Michelson and Fizeau beam combiners for optical interferometry.

The Michelson beam combiners are of a simpler design for small numbers of apertures, but their complexity increases while their efficiency decreases as the number of apertures gets large. Current systems are usually limited to three way beam combiners. The Michelson combiner is also limited in field of view by the path length difference one is willing to correlate over. Since multiple samples for multiple delay lengths must be made within the time constant of the atmosphere, the ability to create large fields of view are limited. The Michelson method measures the raw visibility directly and must be Fourier transformed to form an image.

The Fizeau beam combiner works in the image plane and under ideal conditions produces images similar to using an aperture mask in a large telescope. If the phases (piston error) of the different beams can be adjusted faster than the atmospheric seeing, then a "dirty" image is produced directly. Furthermore, once the technological problems have been solved, adding additional apertures poses no new additional problems and many aperture optical interferometers can be realized. The field of view is only limited by detector and the isoplanetic patch sizes.

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