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

Abstract

We present a portable broadband photoacoustic spectroscopic system for trace gas or aerosol 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 2.5×10-9 cm−1WHz−1/2. In addition to sequential firing mode, the laser source can be operated in multiplexing mode. The firing sequence that determines when and which laser to be activated is programmable, which enables frequency-multiplexing excitation. For demonstration, we modulate 12 lasers at 12 distinct frequencies and a photoacoustic spectrum is acquired within 13 ms.