Progress In Absolute Distance Interferometry

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Abstract
This paper describes the results of recent research undertaken to examine the feasibility of employing laser interferometry to precisely measure absolute distance over extended ranges. Data are presented that show a resolution of 0.03 um (rms) for measurements over distances up to 10 meters. The technology developed for achieving these results is based on two-color, synthetic Michelson interferometry employing a new CO2 laser source. Indeed, the new laser is the key element in this process: it was specifically designed to sequentially switch between four sets of stable R- and P-line pairs and thereby provide a basis for forming simultaneous equations which were employed to greatly reduce the half-wavelength ambiguity typical of single wavelength interferometers. Potential applications to future optical telescopes--particularly the large, multipanel telescopes under consideration for 10-15 years hence--their initial alignment and control, are suggested.

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