Laser heterodyne spectroscopy of ^127I_2 hyperfine structure near 532 nm

Two frequency-doubled diode-pumped Nd:YAG lasers are used to study the hyperfine spectrum of 127I2 near 532 nm by heterodyne spectroscopy. Eight rovibrational transitions between the lowest vibrational level in the ground (X) state to vibrational levels 32–36 in the B state are observed. The measured frequency splittings are used to determine the difference in the hyperfine constants for these transitions. The standard deviation of the theoretical fit to the measured spectra is better than 10 kHz. The root Allan variance of the beat frequency between the I2-locked lasers follows a 1.1×10−2/τ dependence for measurements times τ > 0.002 s and reaches a minimum value of 2.5 × 10−13 (two-sample beat frequency of 70 Hz) at τ = 32 s. A method for accurately determining the absolute frequency of the iodine lines near 532 nm is proposed.