The spontaneous Raman scattering technique is an excellent tool for a quantitative analysis of multi-species gas mixtures. It is a noninvasive optical method for species identification and gas phase concentration measurement of Raman active molecules, since the intensity of the molecule specific Raman signal is linearly dependent on the concentration. Applying a continuous wave (cw) laser it typically takes a few seconds to capture a gas phase Raman spectrum at room temperature. Nevertheless in contrast to these advantages the weak Raman signal intensity is a major drawback. Thus, it is still challenging to detect gas phase Raman spectra in a low-pressure regime with a temporal resolution of only a few 100 ms. In the presented study a fully functional gas phase Raman system for measurements in the low-pressure regime (p ≥ 980 hPa (absolute)) is presented; it overcomes the drawback of the weak Raman effect by using a multipass cavity to enhance the Raman signal. The signal amplification of a retroreflecting cavity is experimentally compared to a near-confocal cavity. A description of this sensor setup as well as of the calibration procedure, which also allows the quantification of condensable gases, is presented. Moreover the functionality of the sensor system is demonstrated in a measurement campaign at an anesthesia simulator under clinical relevant conditions and in comparison to a conventional gas monitor.

Laser based on-line biogas analysis with a Raman probe Zusammenfassung: Die Zusammensetzung von Rohbiogas unterliegt prozessbedingt Fluktuationen, die nachgelagerte Prozesse störend beeinflussen können. In dieser Studie wird ein brenngasunabhängiges, auf den Grundlagen der linearen Raman-Streuung basierendes Messsystem vorgestellt, das in der Lage ist, bei geringem Gasdruck alle relevanten Biogaskomponenten innerhalb einer kurzen Messzeit zu identifizieren und deren Konzentration hochgenau und präzise zu bestimmen.Schlüsselwörter: Online Gaskonzentrationsmessung, Raman-Streuung, Biogas-Analyse, Heizwertbestimmung. Abstract:The composition of raw biogas is subject to fluctuations that can affect downstream processes. In this study a species independent probe based on linear Raman scattering is presented. The sensor system is capable of identifying and quantifying all relevant bio gas components in a low pressure regime with high accuracy and precision within a short measurement time.

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