Blue light-emitting diode-based, enhanced resonant excitation of longitudinal acoustic modes in a closed pipe with application to NO2

Abstract

We present a new, very compact resonant photoacoustic system based on a simple closed pipe, transversally illuminated by an array of blue light-emitting diodes uniformly distributed along the tube to produce an acoustic signal from NO2–N2 samples. The illumination is modulated in a particular way as to produce amplification of the acoustic resonance corresponding to the second longitudinal mode. The linearity of the system for NO2 trace detection is studied. This arrangement provides a simple, compact, and cheap setup, useful for both measuring emissions from diesel engines and teaching photoacoustic spectroscopy in gases.