Study of the hyperfine structure of emission lines of I2 molecules by the method of three-level laser spectroscopy

It is proposed to use narrow optical resonances, corresponding to the hyperfine structure components of emission transitions in I₂, as frequency references to stabilise laser radiation frequency in the spectral range from 0.8 to 1.3 μm. To obtain such resonances and investigate the hyperfine structure of emission transitions, an experimental setup is built which consists of a saturated absorption laser spectrometer and a three-level laser spectrometer. Excitation is performed by the second harmonic of a cw Nd:YAG laser and probe radiation in the range from 968 to 998 nm is generated by an external cavity diode laser. The radiation beams from both lasers are combined in a cell with iodine vapour, excitation in the cell being performed in the regime of two counterpropagating waves. It is shown that upon phase modulation of exciting radiation, narrow resonances, having the form of the dispersion dependence, appear at the centre of Doppler lines in absorption and emission. These resonances can be used as references to stabilise the laser frequency. The results of the study of the hyperfine structure of emission lines at the (J ' = 57, v ' = 32) → (J '' = 58, v '' = 48) transition upon excitation at the (J '' = 56, v '' = 0) → (J ' = 57, v '' = 32) transition are presented.