High sensitivity spectrometer at 3 μm based on difference frequency generation for N2O detection

We report the description of a laser spectrometer based on difference-frequency generation. As a pump laser, we used a master-slave diode laser configuration emitting at 785 nm, while for a signal laser, we used a diode-pumped Nd : YAG laser. The wavelength of the idler radiation is continuously tunable in the spectral region between 2.88 to 3.02 μm. In this range lie the ν
₁
fundamental vibrational symmetric stretching mode of water vapor and the relatively strong combination band ν
₁
+ ν
₃
of nitrous oxide that are both investigated in this work. We show that both molecules can be simultaneously detected by using a simple absorption scheme and by tuning the spectrometer frequency within few gigahertz. A systematic study of pressure broadening for a N
₂
O line has been performed in presence of the main air constituents, i.e., nitrogen and oxygen. Finally, the estimation of the minimum detectable N
₂
O concentration at 500 torr of nitrogen resulted in 2.6(2) ppmV with 0.9-m absorption path-length.