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Zusammenfassung:
We report the development of a trace gas sensor for the detection of atmospheric formaldehyde utilizing a thermoelectrically cooled distributed-feedback quantum cascade laser operating in continuous-wave mode at 5.68 mu m. Wavelength modulation spectroscopy was combined with second harmonic detection and zero air based background subtraction techniques to enhance both detection sensitivity and precision to similar to 2.5 ppbv for H2CO measurement with an integration time of less than 1 second and a 36 m optical path length. A novel analysis technique based on wavelet transform for noise reduction was successfully applied to improve the sensor performance, yielding sub-ppb measurement precision without reducing the fast temporal response.
