Absolute-frequency measurement of the iodine-based length standard at 514.67 nm

The absolute frequency of the length standard at 514.67 nm based on the molecular iodine (I-127(2)) transition of the P(13) 43-0 component a(3) is measured using a self-referenced femtosecond optical comb. This frequency-based technique improves measurement precision more than 100 times compared with previous wavelength-based results. Power- and pressure-related frequency shifts have been carefully studied. The measured absolute frequency is 71.8 +/- 1.5 kHz higher than the internationally accepted value of 582 490 603.37 +/- 0.15 MHz, adopted by the Comite International des Poids et Mesures (CIPM) in 1997.