Portable broadband photoacoustic spectroscopy for trace gas detection by quantum cascade laser arrays

We report a portable broadband photoacoustic spectroscopic system for trace gas detection using distributed feedback quantum cascade laser arrays. By sequentially firing 128 lasers, our system acquires a photoacoustic spectrum covering 565cm^-1 (935-1500cm^-1) with a normalized-noise-equivalent-absorption coefficient of 2.5×10^-9cm^-1WHz^-1/2. The firing sequence that determines when and which laser to activate is programmable, which enables frequency-multiplexing excitation. For demonstration, 12 lasers are modulated simultaneously at distinct frequencies, and a photoacoustic spectrum is acquired within 13 ms. The compactness (28cm×17cm×13cm, 3.5 kg) and low power consumption enable convenient installation for on-site monitoring.