Wavelength Modulation Spectroscopy Detection of N2O Using a Direct-Bonded Quasi-Phase-Matched LiNbO3-Ridge-Waveguide Mid-Infrared Laser

Abstract

We measured nitrous oxide (N2O) concentration by mid-infrared wavelength modulation spectroscopy at a wavelength of 3.87 µm. Mid-infrared laser light from difference frequency generation in a fiber-coupled direct-bonded quasi-phase-matched LiNbO3-ridge-waveguide module is obtained using a diode-pumped Nd-doped yttrium alminum garnet (Nd:YAG) laser at 1064 nm together with a distributed feedback diode laser at 1466 nm. The absorption line of N2O centered at 2583.39 cm-1 (3.871 µm), which originates from the first overtone band of the ν1 asymmetric stretching mode, is measured by second-harmonic wavelength modulation spectroscopy detection. The limits of N2O detection measured by wavelength modulation spectroscopy are found to be 150 ppbv using a 29.9 m Herriott multipass cell at a pressure of 12 kPa. We demonstrated the real-time monitoring of atmospheric N2O using our developed spectrometer with a difference-frequency-generation mid-infrared laser light source.