Acetylene measurement using quantum cascade lasers at 14 µm

It is necessary to control the production process of industrial gases within seconds to get a constant high gas quality. Here, the process gas chromatography with a response time of minutes is state of the art in trace gas monitoring. As an alternative, we developed and present here a spectroscopic trace gas analyzer for acetylene. Because of the given complex gas mixture in a future application an acetylene absorption line at 14μm is selected to avoid cross sensitivities to other gases. For this special wavelength range new quantum cascade lasers (QCL) emitting 380mW peak power at 5 % duty cycle were developed by Nanoplus and University of Würzburg. To achieve a detection limit in the ppb concentration range and weak cross sensitivities the system was optimized towards a high spect ral resolution of 0.013 cm-1. The laser wavelength and the acetylene absorption line are checked by FTIR spectroscopy. In first experiments with the quantum cascade laser spectrometer a noise equivalent concentration of 50ppb acetylene in 1s was achieved.