Description and accuracy tests of an improved lambdameter

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Abstract
An interferometric wavemeter with digital display is described. Fringes of an unknown and a reference wavelength are simultaneously generated through the motion of a moving double comer cube reflector in a Michelson-type interferometer. An electronic device compares the two wavelengths to within one hundredth of a fringe and numerically displays the result. Most of the systematic errors are eliminated by the total superposition of the optical paths of the reference and the measured beams, ensuring a high potential accuracy. As an illustration, we have remeasured with this device the wavelength of the λ = 612 nm radiation generated by a He-Ne laser stabilized on a saturated absorption peak of iodine. The results exhibit a statistical dispersion of ± 6 x 10-9 about a mean value which agrees to within 1.6 x 10 -9 with the more exact result obtained at BIPM