A photoacoustic spectrometer for trace gas detection

A high-resolution external laser photoacoustic spectrometer has been developed for trace gas detection with absorption transitions in coincidence with CO$_2$ laser emission lines (9,2-10,9 $\mu$m: 920-1086 cm$^{-1}$). The CO$_2$ laser operates in 90 CW lines with power of up to 15 W. A PC-controlled step motor can tune the laser lines. The resonance frequency of first longitudinal mode of the photoacoustic cell is at 1600 Hz. The cell Q-factor and cell constant are measured close to 50 and 28 mVcmW$^{-1}$, respectively. The spectrometer has been tested in preliminary studies to analyze the absorption transitions of ozone ($O_3$). The ethylene ($C_2H_4$) from papaya fruit is also investigated using $N_2$ as carrier gas at a constant flow rate