Long-term absolute frequency measurements of 633 nm iodine-stabilized laser standards at NRC and demonstration of high reproducibility of such devices in international frequency measurements

The absolute optical frequency of a 633 nm, I2-stabilized He–Ne laser system is measured with a femtosecond laser frequency comb. Results over a three-year period using chain- and comb-based measurements yield an operating frequency of ff = (473 612 353 602 850 ± 570) Hz for the INMS 3 laser stabilized to the f or a16 component of the 11-5 R(127) transition in 127I2 at the operating conditions specified for the realization of the recommended value of this radiation. The frequency of the NRC INMS 2 laser system has recently been measured with combs at NRC and BIPM and was shown to be reproducible to better than 600 Hz (1 × 10−12) after transport. These results indicate the high level of reproducibility attainable by such widely used optical frequency standards.