We describe the use of a synchronously pumped ringdown cavity for measuring total optical losses, absorption and scattering, in thin optical films of arbitrary thickness on transparent substrates. This technique is compared with a single-pulse ringdown cavity regime and is shown to have a superior signal-to-noise ratio and resolution. We also provide an analysis of the factors affecting the resolution of the technique. Using this ringdown cavity pumped by a conventional mode-locked Ti:sapphire laser, we experimentally detect losses of only 58 ± 9 and 112 ± 9 parts per million in Ta<sub>2</sub>O<sub>5</sub> and SiO<sub>2</sub> films, respectively. To our knowledge, these are so far the lowest losses measured in thin films on stand-alone transparent substrates.
© 2003 Optical Society of America
Georgiy Vaschenko, Yogesh Godwal, Carmen S. Menoni, Claude Montcalm, Richard Blacker, and Daniel Siegfried, "Characterization of Thin-Film Losses with a Synchronously Pumped Ringdown Cavity," Appl. Opt. 42, 4584-4589 (2003)