MIR evanescent-field fiber sensors

Ulrike Willer; Torsten Blanke; Wolfgang Schade

doi:10.1117/12.417455

26 February 2001 MIR evanescent-field fiber sensors

Ulrike Willer, Torsten Blanke, Wolfgang Schade

Author Affiliations +

Proceedings Volume 4205, Advanced Environmental and Chemical Sensing Technology; (2001) https://doi.org/10.1117/12.417455
Event: Environmental and Industrial Sensing, 2000, Boston, MA, United States

Abstract

A compact, tunable and single-mode laser for the mid-infrared (MIW) spectral range is developed by difference frequency generation (DFG) in AgGaS2 and two "off-the-shelf' diode lasers. The MIR laser light is coupled into a silverhalide fiber and at the end of the fiber an infrared detector is used to record the transmitted MIR laser light. If the index of refraction of the fiber material is higher than the one of the surrounding medium the light is guided through the fiber due to total reflection. There are two loss mechanisms that will attenuate the laser intensity when passing through the fiber: (1) The frustrated total reflection (FTR) and (2) the attenuated total reflection (ATR). The FTR is related to a change of the index of refraction while the ATR is related to a change of the absorption coefficient. When tuning the MIR laser over an absorption line of a molecule that is outside of the fiber both, FTR and ATR, contribute to the measured spectral line profile that is recorded by the infrared detector. Similar to the direct laser absorption spectroscopy the recorded line profiles in the case of the evanescent~field spectroscopy can be used for estimating concentrations of molecules. A practical application of the evanescent field fiber sensor is shown as H2S is measured online and insitu at the volcano "Solfatara" in Italy.

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Ulrike Willer, Torsten Blanke, and Wolfgang Schade "MIR evanescent-field fiber sensors", Proc. SPIE 4205, Advanced Environmental and Chemical Sensing Technology, (26 February 2001); https://doi.org/10.1117/12.417455

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KEYWORDS

Semiconductor lasers

Fiber optics sensors

Sensors

Absorption

Fiber lasers

Spectroscopy

Molecules

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