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 565 c m -1 (935-1500 c m -1 ) with a normalized-noise-equivalent-absorption coefficient of 2.5×10 -9 c m -1 W H z -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 (28 c m ×17 c m ×13 c m , 3.5 kg) and low power consumption enable convenient installation for on-site monitoring.