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Open AccessArticle

Improving the Detection Limit in a Capillary Raman System for In Situ Gas Analysis by Means of Fluorescence Reduction

1
Institute for Technical Physics, Tritium Laboratory Karlsruhe, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
2
Instituto Pluridisciplinar, Paseo Juan XXIII-1, Universidad Complutense, 28040 Madrid, Spain
*
Author to whom correspondence should be addressed.
This author is now affiliated to: Institute of Experimental Nuclear Physics, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
This author is now affiliated to: Laser Quantum Ltd., Emery Court, Vale Road, Stockport, SK4 3GL, UK.
Academic Editor: Mark A. Arnold
Sensors 2015, 15(9), 23110-23125; https://doi.org/10.3390/s150923110
Received: 20 July 2015 / Revised: 25 August 2015 / Accepted: 6 September 2015 / Published: 11 September 2015
(This article belongs to the Special Issue Chemical Sensors based on In Situ Spectroscopy)
Raman spectroscopy for low-pressure or trace gas analysis is rather challenging, in particular in process control applications requiring trace detection and real-time response; in general, enhancement techniques are required. One possible enhancement approach which enjoys increasing popularity makes use of an internally-reflective capillary as the gas cell. However, in the majority of cases, such capillary systems were often limited in their achievable sensitivity by a significant fluorescence background, which is generated as a consequence of interactions between the laser light and optical glass components in the setup. In order to understand and counteract these problems we have investigated a range of fluorescence-reducing measures, including the rearrangement of optical elements, and the replacement of glass components—including the capillary itself—by metal alternatives. These studies now have led to a capillary setup in which fluorescence is practically eliminated and substantial signal enhancement over standard Raman setups is achieved. With this improved (prototype) setup, detection limits of well below 1 mbar could be obtained in sub-second acquisition times, demonstrating the potential of capillary Raman spectroscopy for real-time, in situ gas sensing and process control applications, down to trace level concentrations. View Full-Text
Keywords: Raman spectroscopy; capillary; gas analysis; process control; real-time monitoring; instrument development; fluorescence reduction Raman spectroscopy; capillary; gas analysis; process control; real-time monitoring; instrument development; fluorescence reduction
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Rupp, S.; Off, A.; Seitz-Moskaliuk, H.; James, T.M.; Telle, H.H. Improving the Detection Limit in a Capillary Raman System for In Situ Gas Analysis by Means of Fluorescence Reduction. Sensors 2015, 15, 23110-23125.

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