Abstract

The selective and sensitive detection of trace gases in multicomponent gas mixtures by means of absorption spectroscopy requires narrowband continuously tunable laser sources. Using a cw External Cavity Diode Laser (ECDL), tunable between 795 and 825 nm as pump wave, and a diode-pumped monolithic cw Nd:YAG laser at 1064 nm as signal wave, we produce narrowband (a few MHz) mid infrared laser light between 3.16 and 3.67 μm by Difference-Frequency Generation (DFG) in bulk LiNbO₃. Many compounds of interest (CH₄, H₂CO, …) show characteristic strong absorptions in this fundamental wavelength region. A multipass cell employed as a gas chamber with an effective path length of 36 m is used in combination with sensitive IR detectors for recording absorption spectra. True multicomponent capability of such a laser spectrometer requires a broad, narrowband, continuous tunability in the mid-IR.

© 1998 IEEE