Comparison of the spectral excitation behavior of methane according to InP, GaSb, IC, and QC lasers as excitation source by sensor applications.

The MIR wavelength regime promises better gas detection possibilities than the NIR or the visible region because of the higher absorbencies simulated by HITRAN. In the MIR region are many important absorption lines of significant gases, which are relevant in healthcare, production supervision, and safety and environmental monitoring. One of those gases is methane. CH4 shows significant variations in absorbance with a maximum at 3.3 μm, which results in low detection limits in the range of low ppm. Interband-cascade- and quantum-cascade-based lasers emit at higher wavelengths, where the absorbencies of methane are higher. The comparison is done by analyzing the performance of two spectroscopy applications: tunable diode laser absorption spectroscopy and quartz-enhanced photoacoustic spectroscopy.