Fast and accurate extraction of ultrahigh quality factors from cavity ringdown measurement

Cavity ringdown spectroscopy is an essential test to measure ultrahigh quality factor (UHQ) optical cavities, which is, however, frequently misinterpreted due to lack of a specified analysis guideline. Here we clarify the basic property of cavity ringdown and present a step-by-step method that enables extraction of the overall quality factor, as well as the intrinsic loss and coupling state of UHQ cavities with better fidelity and simplicity than prior schemes. Our work can facilitate an accurate design and characterization of UHQ cavities for ultra-low noise lasers, high finesse reference cavities, and ultra-narrow optical filters.