A description is given of an electromechanical scanning Fabryndash;Perot interferometer, designed primarily for rapid and precise wavelength comparisons and spectral line profile studies under vacuum conditions. It has a continuously variable path difference range of up to 1 m. Wavelengths may be compared with the present primary kryptonhyphen;86 standard to the uncertainty of this standard (plusmn; 4 parts in 109). Provision is also made for automatic control of plate parallelism and plate separation.
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