Effect of the 129I impurity on the radiation frequency of a stabilised He – Ne/127I2 laser

The radiation frequency of a He – Ne/¹²⁷I₂ laser stabilised to the hyperfine structure component of molecular iodine exhibits shifts caused by the presence of impurities in the iodine cell. The specific effect of the ¹²⁹I impurity on the radiation frequency of a stabilised laser is considered. It is shown that even for a 0.25 % concentration of ¹²⁹I, the frequency shift in a He – Ne/¹²⁷I₂ laser caused by this isotope plays a decisive role. To exclude the possible effect of other iodine isotopes on the accuracy of reproducibility of the frequency of metrological lasers, it is expedient to carry out the laser fluorescence test of the cells to check for the presence of heteroisotopic molecular iodine impurity.