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 length-stabilized ring-down cavity, which leads to interference between the internally circulating light and that which is fed back through the cavity input mirror. Using a feedback cavity with a finesse of 16, we demonstrate that this effect increases the ring-down cavity time constant from 210 µs to 280 µs, corresponding to an increase of finesse from 2.7105 to 3.6105. Finally, we show that with the addition of a second feedback cavity, we observe ring-down times as long as 0.50 ms, equivalent to a finesse of 6.4105 and an effective mirror transmittance of 4.9106.
and Hodges, J.
Coupled-cavity ring-down spectroscopy technique, Optics Letters, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=911352
(Accessed December 10, 2023)