A 3.5-mW continuous-wave difference-frequency source around 3 μm for sub-Doppler molecular spectroscopy

We report the development of a mid-infrared tunable coherent radiation source, based on difference-frequency generation (DFG). The signal and pump beams coming from two cw rare-earth-doped amplifiers are mixed into a periodically-poled LiNbO3 crystal to produce radiation in the 2.9–3.5 μm spectral range. For the first time to our knowledge, an output power of several mW has been achieved. We show that such a power can be exploited for high-resolution investigation of molecular absorption spectra. Saturation Lamb-dips have been observed for a number of ro-vibrational transitions belonging to the CH4 ν3 fundamental band.

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