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 cm(-1) (935 1500 cm(-1)) with a normalized-noise-equivalent-absorption coefficient of 2.5 x 10(-9) cm(-1) WHz(-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 cm x 17 cm x 13 cm, 3.5 kg) and low power consumption enable convenient installation for on-site monitoring. (C) 2020 Optical Society of America