Design of Stellar Interferometers I

William J. Tango (University of Sydney)

Abstract:

I will review some of the key design principles that flow from (a) the science goals of the interferometer, (b) the limitations imposed by the atmosphere and (c) instrumental effects that can degrade the measured fringe visibility.

The science goals will of course dictate the basic design parameters of any interferometer. In particular, the wavelength coverage, bandwidth, etc., will be determined by the scientific program.

Although the fundamental limits of performance are ultimately set by photon statistics, "seeing" due to turbulence in the atmosphere is biggest problem in stellar interferometry, and the main strategies for reducing the deleterious effects of the atmosphere will be discussed. These include restricting the size of the input apertures, using adaptive optics, spatial filtering, and using appropriate sampling times.

Key instrumental issues are phase stability, optical quality, and achieving high throughput. Phase stability is important since instrumental effects such as vibration in moving components (the path compensator) or in plant (air conditioning, etc.) can significantly degrade performance. Due to the large number of optical elements in most interferometer designs, both optical quality and transmission of individual elements must be very high. Other physical optical aspects of the system, including polarization and diffraction, must be taken into account.

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Bibliography:

• Design of stellar interferometers
  T. ten Brummelaar
  in "Principles of Long Baseline Stellar Interferometry," P. R. Lawson, ed., (Jet Propulsion Laboratory: 1999) p. 87.

• Optical interferometry
  A. Quirrenbach
  Ann. Rev. Astron. Astrophys. 39, 353 (2001).

• Michelson Stellar Interferometry
  W.J. Tango and R.Q. Twiss
  Progress in Optics 17, 239 (1980)