4.6 µm-band difference frequency generation and CO isotopologue detection

There are many strong absorption lines of environmental gases in the mid-infrared region in atmospheric air, including those of greenhouse effect gases. Reported is difference frequency generation in a direct-bonded periodically poled LiNbO3 ridge waveguide in the 4.6 µm band, which is the most appropriate wavelength range for observing carbon monoxide absorption spectra. It is also shown that isotopologue absorption lines can be detected using the output light generated in a waveguide with mature telecommunication band laser diode light sources. The direct-bonded ridge waveguide consisted of a 50 mm-long chip and its wavelength conversion efficiency was approximately 4%/W.