Spectroscopy of CH4 with a difference-frequency generation laser at 3.3 micron for atmospheric applications

The 3.25 micron spectral region is very suitable for the in situ sensing of CH₄ in the troposphere and the lower stratosphere with light-weight laser sensors. Several transitions of the strong fundamental ν ₃ band of CH₄ are revisited in this spectral region using an ultra-compact Difference-Frequency Generation (DFG) laser. Accurate intensities as well as self-broadening coefficients are reported for several manifolds that are particularly relevant to the monitoring of CH₄. The study is extended to over hundred transitions reachable over the tunability range of the laser. Moreover, this DFG laser is the light source of a new, highly-compact CH₄ laser spectrometer to be operated from weather balloon. The CH₄ laser sensor is described and preliminary flight results are reported.