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Abstract We performed Doppler-free spectroscopy on the P(40)52-0 and P(52)53-0 lines of molecular iodine ( 127 I 2 ) near the 1 S 0 - 3 P 2 metastable transition of Yb at 507 nm. The frequency instability of an external-cavity diode laser locked to the observed hyperfine transitions of the 127 I 2 lines reached a level below 1.0 × 10 −12 , at the average time τ of the measurement of >10 s. The absolute frequency of the laser locked to the hyperfine transitions was measured with an uncertainty of 8 kHz (fractionally 1.4 × 10 −11 ) using an optical frequency comb. The hyperfine transition intervals were fitted to a four-term Hamiltonian to validate the measurements and calculate the hyperfine constants of the iodine lines. The observed 30 hyperfine transitions of the P(40)52-0 and P(52)53-0 lines of 127 I 2 can be used as optical frequency references to investigate the 1 S 0 - 3 P 2 transition of Yb atoms.
Sakamoto et al. (Fri,) studied this question.