Sub-Doppler laser spectroscopy of molecular iodine at 578 nm

We carry out sub-Doppler laser spectroscopy of hyperfine components of rovibrational transitions of molecular iodine at 578 nm using second harmonic generation of an 1156-nm external-cavity diode laser. The absolute frequencies of the hyperfine components can be determined by using an optical frequency comb to referenced to the Coordinated Universal Time of the National Metrology Institute of Japan. The hyperfine components at 578 nm can be good frequency references for the ¹S_o^-3P_o clock transition in atomic ytterbium.