Abstract

The absorption lines of the ¹²⁷I₂ molecule near 532 nm were investigated by using two frequency-doubled diode-laser-pumped nonplanar ring lasers emitting 300 mW at 1064 nm. Second harmonic generation is accomplished by using 8 mm long MgO:LiNBO₃ monolithic resonant doublers.¹ A thermal control loop maintains the doubling crystal on resonance with the laser. The 532 nm output of each doubler is the source used for FM saturation spectroscopy² of iodine. The dispersion signal of a Doppler-free line is fed back through a servo amplifier into the piezoelectric frequency actuator of the laser, thus locking the laser to that line. The frequency difference between iodine hyperfine transitions is obtained by locking each laser to a different transition and measuring the beat-note frequency between the lasers. Accuracy in the kilohertz range is achieved because of the relatively low frequency fluctuations of the diode-laser-pumped lasers. By locking a diode-laser-pumped Nd:YAG to the iodine Doppler-free transition we have demonstrated the possibility of a source with absolute stable and reproducible frequency. The precise spectroscopic characterization of iodine line shifts as a function of operating conditions enables us to optimize its performance for coherent communication, optical frequency standards, and me­trology applications.

© 1992 Optical Society of America