Modulation transfer spectroscopy of I₂ enhanced by an external optical cavity

A novel high sensitive laser spectroscopy technique, double-frequency phase modulation ring-cavity enhanced modulation transfer spectroscopy, is presented. Using ring-cavity absorption enhancement and double-frequency phase modulation with one crystal, this technique combines the advantages of high sensitivity, high resolution, Doppler-free with modulation transfer spectroscopy and high signal to noise ratio with ring-cavity enhancement technique. The hyperfine spectrum of molecular ¹²⁷I₂ with high signal to noise ratio was observed at 532 nm. The experimental results show that this new spectroscopy technique enhances detection sensitivity greatly compared with traditional modulation transfer spectroscopy. It is promising for improvements of ultrasensitive spectroscopy and laser frequency stabilization.