Modulation Transfer Spectroscopy of ${}^{127}I_{2}$ Hyperfine Structure at 561 nm

Hyperfine structures of ¹²⁷I₂ absorption transitions near 561 nm are observed via modulation transfer spectroscopy by a homemade Nd:YAG monolithic nonplanar ring laser with its second harmonic generation (SHG) using a single-pass PPMgO:LN crystal. The observed I₂ transitions are assigned according to theoretical calculation results of the I₂ B-X transition. Two Nd:YAG lasers are locked to the 15th component of the ¹²⁷I₂ P(58)22-1 transition, and the measured frequency stability of these lasers is 1 × 10^-13 for a 1-s averaging time. Frequency shifts with changing iodine cell vapor pressure and pump power are measured by observing the heterodyne beat between two I₂-stabilized lasers.