We have demonstrated the production of ∼ 1.9 μm near-infrared radiation by using difference frequency generation within a 5% MgO doped PPLN crystal by coupling ∼735 nm radiation from a tunable external cavity diode laser with relatively high powered 532 nm radiation from both Nd:YVO3 and Nd:YAG lasers. The radiation produced is of low power, ∼15 μW, and was used in conjunction with the sensitivity enhancing techniques of wavelength modulation spectroscopy (WMS) and cavity enhanced absorption spectroscopy (CEAS). Experiments were carried out on rotationally resolved transitions in the combination bands of NH3 and CO2 in the 1.9 μm region. An α min∈ value of 3.6×10-6 cm -1 Hz-1/2 was achieved for WMS measurements on CO 2. A comparable α min∈ value of 2.2×10-6 cm-1 Hz-1/2 was achieved for NH3 using CEAS. The low NIR power indicates that despite the level of MgO doping quoted for the crystal, under prolonged exposure photorefractive damage has occurred. © 2009 Springer-Verlag.
