DFG was confirmed to be an effective technique to realize stable mid-infrared pulse output, even when the idler wavelength reached at 3.8 μm. High quality pulse pump laser and signal laser could still be constructed with average power high enough for efficient DFG conversion, even if their wavelengths were situated at the edges of their gain spectra. Conversion efficiency saturation was likely to happen in DFG at long idler wavelength mainly due to material adsorption. Improvement could be expected by using signal source with wider spectrum.