Photoacoustic harmony: Using musical concepts to study mixed gases through PA spectroscopy

Photoacoustic Spectroscopy was applied to study the intensity of musical notes in harmony created by the photoacoustic signals of ethylene (C2H4) and sulfur hexafluoride (SF6) gases. Two CO2 lasers with a wavelength of 10.6 μm were modulated using two separate mechanical choppers. It was observed that musical notes with a frequency approximately that of the fundamental frequency of the resonator had higher intensity peaks than those further away. To equilibrate the intensities of these notes for fuller tones in the musical chords of interest, a second resonator, sulfur hexafluoride, having vastly different resonance properties from ethylene, was added to the gas cell. It was observed that this only moderately affected the outcome for the overall tone of the chords of interest. However, as expected, sulfur hexafluoride offered a more dynamic range of tones due to its large variance in resonance frequency with concentration.