Abstract
Frequency separations have been measured of some of the 127I2 saturated absorption features used to stabilize the 633 nm He-Ne laser. The frequencies are measured with uncertainties approaching 10 kHz by a digital beat frequency method, using lasers locked to the absorption features by a third harmonic technique and having stabilities of 10 kHz ( delta nu / nu =2*10-11) for a 10 second observation time. Wavelength measurements are made on a laser locked to the 'd' absorption feature, using a krypton-86 lamp in conjunction with a scanning Fabry-Perot interferometer. The value lambda vac is 632991178.3 fm with a statistical uncertainty of +or-0.8 fm ( delta lambda / lambda =+or-1.2*10-9).