Supernarrow saturated absorption resonances in weakly coupled two resonantoptical cavities

The advantages of the weakly coupled two resonant optical cavities (hereina fter referred to as three-mirror cavity) used for observation of the supern arrow saturated absorption resonances are shown. Among these advantages we can name: (a) the possibility to control the intensity in the cavity with t he inside absorbing cell which is important when the gain and absorption sa turation parameters differ significantly; (b) the resonances observation fr om the 'passive' side of the three-mirror cavity permits us to decrease dra stically the influence of the reflected signal from the detector; (c) if in stead of the absorbing cell an active system is put in (gain plus absorptio n), it is possible by tuning the operating mode of the active interferomete r to obtain many-fold gain of the supernarrow resonance amplitude.