High-contrast saturated absorption spectrometer with a grating reflector as an optical frequency locker

By optical feedback of signals obtained with a high-contrast saturated absorption spectrometer as a reference frequency selector, diode laser frequency has been locked to the hyperfine transition line of a Cs atom. We used a grating instead of a mirror for optical feedback to avoid feedback of unwanted modes, because such modes cause mode hopping or generate another frequency component, whose intensity does not decrease even after it passes through an atomic cell twice. Long-term frequency stability has been improved by compensating the cavity length for phase fluctuations.