Düsseldorf 2007 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 2: Diagnostische Methoden

P 2.2: Vortrag

Montag, 19. März 2007, 11:30–11:45, 6C

Mid Infrared Absorption Spectroscopy Using Optical Cavities and Quantum Cascade Lasers — •Stefan Welzel¹, Paul B. Davies², Richard Engeln³, and Jürgen Röpcke¹ — ¹INP Greifswald, 17489 Greifswald, Germany — ²University of Cambridge, Cambridge CB21EW, UK — ³Eindhoven University of Technology, 5600 MB Eindhoven, NL

Optical cavities have been utilised for more than fifteen years with the aim of achieving an extremely sensitive absorption technique with hundreds of metres path length. Cavity Ring-Down Spectroscopy (CRDS) and Cavity Enhanced Absorption Spectroscopy (CEAS) are two frequently used methods that have been applied in the visible and near IR spectral ranges. The extension of optical cavity based methods to the mid IR has been hampered due to the lack of suitable light sources. Nowadays quantum cascade lasers (QCL) are candidate light sources to overcome these constraints. CRD experiments using a pulsed QCL at 8.3 µm as well as CEA experiments using a cw-QCL at 7.7 µm have been performed where both lasers were operated at room temperature. Usually, the concentrations for reference gases determined with the QCL-CRD approach exhibit discrepancies from the known values. The reason for this is the inherent frequency chirp of the pulsed QCL which is typically bigger than the absorption line width. In order to avoid these obstacles, a cw-QCL was tuned with a current ramp to obtain a CEA spectrum. An effective absorption path length of 700 m could be achieved resulting a sensitivity of 1.5 · 10⁻⁶ cm⁻¹, i.e. a detection limit of 10¹¹ cm⁻³ for nitrous oxide.