Absolute frequency measurements for emission transitions of molecular iodine in the range of 1053–1068 nm

Results of high-precision frequency measurements are presented for certain components of the ¹²⁷I₂ hyperfine structure, which correspond to emission transitions of the B – X band in the range of 1053–1068 nm. The frequencies are measured by using a femtosecond optical frequency synthesiser based on a Ti:sapphire laser. The hyperfine structure is resolved by the method of threelevel laser spectroscopy. The frequency-doubled cw Nd : YAG laser is used as an excitation radiation source, and the probe radiation in the range of 1050–1070 nm is generated by an external-cavity diode laser. The frequencies of both lasers are simultaneously locked to those of two adjacent hyperfine structure components of iodine lines, which have a common upper level. Correspondingly, the frequency of the Nd : YAG laser is locked to the frequency of the absorption transition component, and the diode laser frequency – to the frequency of the emission transition component. The radiation frequency of the diode laser 'locked' in this way is measured. Frequencies of 18 hyperfine structure components for six emission lines corresponding to the bands (32–54) and (32–53) are measured. The relative uncertainty of the measurement is 8 × 10^-10.