Abstract
The iodine stabilization system is usually used as an optical frequency standard. We report the absolute frequency measurement of 127I2 P(28) (24-0) lines. The frequency of iodine transitions is several GHz away from the Li+ ion transition and can be used as reference for lithium ion spectroscopy. In this experiment, we use 1097 nm external-cavity diode laser and a double system to produce 548.5 nm light, and use modulation transfer spectroscopy to obtain the iodine spectrum. We measure a1, a10, a15 lines, and they are measured at a vapor pressure of 7.8 Pa. As a result, we correct them by the pressure shift which is measured to be 8.9(1.2) kHz/Pa. The final results of the a1, a10, a15 are 546437908826(12) kHz, 546438483384(12) kHz, and 546438771985(12) kHz respectively. The results agree with the calculated values of IondineSpec5. The effect of pressure and power broadening are also investigated. For the future work, we will measure other transitions of molecular iodine between 540-550 nm, and some of them can also be used as references for lithium ion spectroscopy.