A mid-infrared spectrometer based on difference frequency generation

A mid-infrared spectrometer operating in the range from 3.42 to 4.78μm based on difference-frequency mixing of a tunable Ti:Sapphire laser and a diode-pumped monolithic Nd:YAG laser in periodically poled LiNbO3 (PPLN) crystals was developed. A system line width of about 36 MHz was obtained. An energy conversion efficiency of 0.6 mW/W2 was obtained at 3.70μm. The direct absorption spectra of pure methane and pure carbon dioxide samples were measured to test the performance of the spectrometer.