Laser Absorption Spectrometry - Cavity Enhanced Absorption Spectrometry - Continuous Wave Cavity Enhanced Absorption Spectrometry

Continuous Wave Cavity Enhanced Absorption Spectrometry

The group of CEAS techniques that has the largest potential to improve is that based on a continuous coupling of laser light into the cavity. This requires however an active locking the laser to one of the cavity modes. There are two ways in which this can be done, either by optical or electronic feedback,. Optical feedback (OF) locking, originally developed by Romanini et al. for cw-CRDS, uses the optical feedback from the cavity to lock the laser to the cavity while the laser is slowly scanned across the profile (OF-CEAS). In this case, the cavity needs to have a V-shape in order to avoid OF from the incoupling mirror. OF-CEAS is capable of reaching sensitivities ~10−8 range, limited by a fluctuating feedback efficiency. Electronic locking is usually realized with the Pound-Drever-Hall (PDH) technique, and is nowadays a well established technique, although it can be difficult to achieve for some types of lasers. It has been shown by that also electronically locked CEAS can be used for sensitive AS on overtone lines.

Read more about this topic:  Laser Absorption Spectrometry, Cavity Enhanced Absorption Spectrometry

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