title: Coupled-cavity ring-down spectroscopy technique.
abstract: We present a technique called coupled-cavity ring-down spectroscopy (CC-RDS) 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. Using a 74 cm long ring-down cavity and a feedback cavity with a finesse of 16, we demonstrate that this effect increases the decay time constant from 210 μs to 280 μs, corresponding to an increase of finesse from 2.7×10(5) to 3.6×10(5). Finally, we show that with the addition of a second feedback cavity, we observe ring-down times as long as ~0.5 ms, which is equivalent to (1-R)≈4.9×10(-6), where R is the effective mirror reflectivity.
authors: National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
authors: Jérémie
authors: J
authors: Courtois
authors: Joseph T
authors: JT
authors: Hodges