Detection and spectroscopy of the ν1+ ν3 band of N 2O by difference-frequency spectrometer at 3 μm

Abstract

We report the realisation of a laser spectrometer in the mid-infrared spectral region based on difference-frequency generation in a periodically poled LiNbO 3 crystal. Tunable coherent radiation around 3 μm was produced by mixing a diode-pumped monolithic cw Nd-YAG laser and an injection-locked diode laser at 0.785 μm. High sensitivity N 2O detection was demonstrated by observing pure absorption spectra of lines in the ν 1+ ν 3 combination band. We estimate a minimum detectable pressure of pure N 2O of 1×10 −2 Pa with 0.9 m absorption path-length, corresponding to an absorbance of 3×10 −4. Nitrous oxide was also detected in presence of O 2, N 2 and air. Collisional broadening coefficients for the P(33) line at 3447.678 per cm are reported for N 2ON 2 and N 2OO 2 mixtures.