A multiple-reflection cell suited for absorption measurements in shock tubes
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The improvement of the detection limit in optical concentration measurements by means of multiple-reflection cells (MRC) has become a well established method in absorption spectroscopy.
To apply such an experimental method to shock tubes, several technical problems have to be solved. The use of special optical cells showing mechanical ruggedness is required.
In this report we present such a MRC designed for a cylindrical shock tube with an inner diameter of 100 mm. By means of 8 mirrors (optical coated stainless steel) the absorption length has been increased by almost one order of magnitude (863 mm) while the optical path is kept in one plane. The use of fixed flat mirrors provides a very high mechanical stability, which facilitates the application to shock tubes.
The first experimental results with this MRC were obtained by measuring the thermal decomposition of O3 behind incident shock waves using an UV laser beam. A direct comparison to the signals simultaneously detected by the use of the conventional absorption length (i.e. the tube diameter of 100 mm) documents the suitability of this MRC for applications in chemical kinetics.
Key wordsChemical kinetics Detection sensitivity Multiple-reflection cell UV absorption spectroscopy
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