Abstract: A coupled-cavity ring-down spectrometer utilizes an optical resonator to increase the reflectivity of ring-down cavity mirrors by adding external optical cavities that recycle light to the main cavity. These input and output cavities are made up of at least one coupling mirror and at least one movable recycling mirror. The movable recycling mirrors are coupled to at least one piezoelectric transducer, which generates movement of the recycling mirrors. The coupled-cavity ring-down configuration achieves higher spectrometer finesse, sensitivity and dynamic range.

Abstract: An optical resonator by which reflectivity of ring-down cavity mirrors can be altered and enhanced by adding external optical cavities that recycle light to the main cavity. A coupled-cavity ring-down spectroscopy (CC-RDS) is used for controlling the finesse of an optical resonator. Applications include extending the sensitivity and dynamic range of a cavity-enhanced spectrometer as well as widening the useful spectral region of high-reflectivity mirrors. CC-RDS uses controlled feedback of the probe laser beam to a ring-down cavity, which leads to interference between the internally circulating light and that which is fed back through a cavity mirror port.