Appl. Phys. Express 5, 022701 (2012)

By phase-locking two independent clock lasers to a common optical frequency comb, scientists in Japan have successfully transferred the high stability of a master clock laser to a slave clock laser, which usually exhibits inferior performance. The team, from the National Institute of Information and Communications Technology (NICT) and the Japan Science and Technology Agency, say that the technique will prove useful for applications related to optical frequency standards and ultraprecise spectroscopy. The 729 nm master clock laser used in the experiment is reportedly the most stable clock laser at NICT, whereas the 698 nm slave clock laser, being based on a 87Sr transition, is inherently less stable. The researchers used an optical frequency comb generated by a Ti:sapphire laser to bridge the frequency gap between the two lasers and applied a feedback-signal driven acoustic optical modulator to correct for fluctuations in the frequency of the slave laser. They measured a factor of two improvement in stability (from 4.4 × 10−15 to 1.9 × 10−15) for the phase-locked slave laser. The researchers are now attempting to reduce thermal noise and improve the inherent stability of the slave laser by cooling pure-silicon optical cavities to temperatures of around 120 K.