Photoacoustic thermometer: frequency shift of the photoacoustic signal due to analyte temperature variation

Photoacoustic (PA) Spectroscopy has rapidly developed for a wide variety of uses in recent years and continues to do so. This study describes how temperature affects the PA signal produced by ethene in order to develop a PA thermometer. Harmonics of three different length PA cells are examined to show how the shift in signal frequency changes with respect to cell length. The harmonic number was varied as well to describe how the change in signal frequency changes with respect to harmonic number. A CO2 laser was used in combination with a chopper to modulate the laser light. The signal was observed within a 65°C range from approximately 5°C to 70°C. A Dewar vacuum flask was used to insulate around the PA cell as the temperature was varied. Ice and thermal strips were used to lower and raise the temperature, respectively. Data was taken from low temperatures to high. The PA cell resonance frequency was seen to increase as the temperature was raised. Preliminary results show that data from graphs of resonance frequency v. the square root of absolute temperature fit 2nd order polynomials. Higher harmonics could be used to design more sensitive instruments. Sincerely