METHOD AND APPARATUS FOR TRACE GAS DETECTION USING INTEGRATED WAVELENGTH MODULATED SPECTRA ACROSS MULTIPLE LINES

摘要

An apparatus and technique are invented that enhance the sensitivity of a spectrometer for trace gas detection by employing wavelength modulation spectroscopy (WMS) and integrating the absolute value of the recorded spectra across multiple absorption lines (features) of the species. The sensitivity is further enhanced by conducting WMS with large modulation depths. This technique is implemented using a continuously tunable external cavity CW quantum cascade laser to record the second harmonic wavelength modulated spectra of N02 across the peak of the R-branch from 1629.5 cm-1 to 1633.9 cm-1. By integrating the absolute value of the resulting spectra, the detection sensitivity of N02 is improved by a factor of 40 compared to the sensitivity achieved using single line WMS with the same apparatus.