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We report the first absolute wave number measurements made using a sophisticated version of the sigmameter. This apparatus is composed of four double Michelson type interferometers with fixed path differences. All path differences are calibrated using four reference lines given by single-mode lasers stabilized on iodine lines whose absolute wave numbers are known to better than one part in 109. This permits us to make absolute wave number measurements of radiation from a cw laser to a precision of the order of one part in 108 (≊5 MHz) and from a pulsed laser to a precision limited only by its spectral width. As examples, using a cw tunable dye laser, several new measurements of 20Ne lines have been achieved with the expected precision (10−8). Measurement of a pulsed laser frequency has also been done with an accuracy of the order of one part in 106.
Juncar et al. (1982) studied this question.