Saturated absorption inside a Fabry-Perot resonator - Spectroscopic and metrological applications

A saturated absorption technique for spectroscopy and metrology based on the use of a Fabry-Perot resonator is presented and applications of the technique are reported. The method involves the placing of the absorption cell within a Fabry-Perot resonator, allowing a considerable increase in sensitivity if the reflection coefficient of the mirrors is close to 1. For saturated absorption spectroscopy of a weakly saturated dilute media, the signal level is doubled and a Gaussian beam is obtained, permitting the observation of weak and fine lines. The technique has been applied to the study of the high-resolution hyperfine structure of iodine around 612 nm, in which the hyperfine dissociation of the R(47) 9-2 line was observed, and to the improvement of the frequency stability and reproducibility of an iodine-stabilized He-Ne laser.