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

Hyperfine structures of
¹²⁷
I
₂
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
I
₂
transitions are assigned according to theoretical calculation results of the
I
₂
B-X transition. Two Nd:YAG lasers are locked to the 15th component of the
¹²⁷
I
₂
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
I
₂
-stabilized lasers.