Abstract
The authors developed a fast simultaneous method in detecting multi-gases using quantum cascade laser (QCL) based photoacoustic (PA) spectroscopy. We demonstrated the simultaneous measurement of CO and SO2 concentrations using two QCLs working at 4.56 and 7.38 μm, corresponding to the absorption bands of CO and SO2, respectively. The modulation frequencies of the two QCLs were 234 and 244 Hz. The response time was 0.6 seconds. A computer sound card was used to process the PA signals. Fast Fourier transform was an essential step to get the amplitudes of the PA signals at different frequencies. The concentration of each gas can be obtained from the PA signal amplitude at the corresponding modulation frequency.
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