Description:
<jats:p>The light absorption of a solid sample in the 8.5 μm region is measured via cavity ring down (CRD) absorption spectroscopy, using a free electron laser (FEL) as a source of widely tunable infrared (IR) radiation. A 3 mm thick zinc-selenide (ZnSe) window is used as a substrate for a 20–30 nm thick C60 film. On top of the structureless absorption due to ZnSe (&lt;340 ppm), one of the well-known fundamental IR absorption lines of C60 is measured with monolayer sensitivity.</jats:p>