Photo Acoustic Spectroscopy of 〖NO〗_2-N_2 and 〖NO〗_2-Ar Using Two Independent Sources

A cylindrical PA cell is designed and constructed; also the Q factor, thermal and viscous loss depths and resonance frequencies are calculated for each buffer gas. The NO2 sample gas and Ar buffer are inserted to the cell and minimum concentration is detected 47.5 ppm at 700 mbar. In this experiment the cell is illuminated with a chopped CW CO2 laser beam. Then the buffer gas is replaced by N2 in the same pressure and minimum detectable concentration is obtained to be 62.2 ppm. The output of another CW Nd:YAG laser after passing through the chopper illuminates the cell in the same experimental condition giving 32.8 and 16.2 ppm minimum detectable concentration for Ar and N2 buffers, respectively. For these four experiments, the magnitude of PA signals are plotted against pressure and it is shown that the slope of the graph when using Nd:YAG laser and N2 buffer gas is approximately 2 times greater than the others.