Gas absorption spectroscopy using GaAs/AlGaAs quantum cascade lasers and a hollow waveguide absorption cell

摘要

In this contribution, the first application of the recently developed GaAs/AlGaAs quantum cascade lasers and hollow waveguides in gas sensing spectroscopy is demonstrated. A multimode GaAs/AlGaAs quantum cascade laser tuned to an emission maximum at 10.009 mum is used to investigate a mid-infrared absorption of ethene at atmospheric pressure. The laser radiation is focused onto the entrance of a 434 mm long, gas-tight terminated hollow waveguide and it is collected after passing it. Well defined mixtures with ten differnet concentrations of helium and ethene are flushed through the waveguide. The radiation is analyzed using a Fourier-transform infrared spectrometer (FTIR) equipped with a mercury-cadmium-telluride detector. the obtained discrete ethene spectrum is compared to a calculated spectrum finding a good agreement. A detection threshold of 250 ppm and a response time in the range of 100 ms have been obtained with the current setup.