title: Actively coupled cavity ringdown spectroscopy with low-power broadband sources.
abstract: We demonstrate a coupling scheme for cavity enhanced absorption spectroscopy that makes use of an intracavity acousto-optical modulator to actively switch light into (and out of) a resonator. This allows cavity ringdown spectroscopy (CRDS) to be implemented with broadband nonlaser light sources with spectral power densities of less than 30μW/nm. Although the acousto-optical element reduces the ultimate detection limit by introducing additional losses, it permits absorptivities to be measured with a high dynamic range, especially in lossy environments. Absorption measurements for the forbidden transition of gaseous oxygen in air at ∼760nm are presented using a low-coherence cw-superluminescent diode. The same setup was electronically configured to cover absorption losses from 1.8×10-8cm-1to 7.5% per roundtrip. This could be of interest in process analytical applications.
authors.affiliation: Fraunhofer Institute for Physical Measurement Techniques, Heidenhofstrasse 8, 79110 Freiburg, Germany. christian.petermann@ipm.fraunhofer.de
authors.forename: Christian
authors.initials: C
authors.lastname: Petermann
authors.forename: Peer
authors.initials: P
authors.lastname: Fischer