Broadband Gas QEPAS Detection Exploiting a Monolithic DFB-QCL Array

Mid-infrared spectral “fingerprints” of many hazardous and harmful gaseous substances are characterized by broad absorption bands, resulting from the merging of several absorption lines corresponding to ro-vibrational transitions. Broadband absorption spectroscopy is fundamental to detect and discriminate these substances. Here we report on a quartz-enhanced photoacoustic spectroscopy sensor for broadband absorbers detection, employing a monolithic array of 32, individually addressable, distributed-feedback quantum cascade lasers as the excitation source. This light source combines a fast tuning speed with a large tuning range, from 1190 cm−1 to 1340 cm−1 together with a high stability. The QEPAS sensor was tested for nitrous oxide (N2O) and methane (CH4) detection, exhibiting absorption features in the laser source emission spectral range. The two broad P- and R- absorption branches of N2O have been accurately reconstructed, as well as several absorption features of CH4, for gas concentrations ranging from 200 to 1000 part-per-million in nitrogen.