To demonstrate the potential of the cavity ringdown technique in mid-infrared spectroscopy of thin film samples, we measured absorption losses in a C<sub>60</sub> film on a BaF<sub>2</sub> substrate using a tunable optical parametric amplifier source. With a Brewster angle sample geometry, we achieved a fractional loss sensitivity as small as 1.3 × 10<sup>−7</sup> with 1.5 cm<sup>−1</sup> resolution, an improvement in sensitivity of 2 orders of magnitude compared to standard Fourier transform infrared methods. At an absorption sensitivity of 5 × 10<sup>−7</sup>, spectra of several C<sub>60</sub> overtone lines were recorded.
© 2002 Optical Society of America
George A. Marcus and H. Alan Schwettman, "Cavity Ringdown Spectroscopy of Thin Films in the Mid-Infrared," Appl. Opt. 41, 5167-5171 (2002)