Widely tunable difference frequency generation source for high-precision mid-infrared spectroscopy

We have developed a widely tunable mid-infrared difference frequency generation (DFG) source by mixing similar to 1 W Ti:sapphire laser and 6 W Nd:YAG laser beams in a 50-mm MgO-doped long periodically poled lithium niobate (MgO:PPLN). The power of the DFG source is > 2 mW over the tuning range of 2.66-4.77 mu m and its free-running linewidth is about 100 kHz. Combining various frequency stabilisation schemes for the Nd:YAG laser and the Ti:sapphire laser, the DFG frequency can be precisely controlled. Besides, its frequency can be determined better than 12 kHz by measuring the Ti:sapphire laser frequency using an optical frequency comb. Two high resolution spectroscopic studies on (CO2)-C-12-O-16 molecule are demonstrated using this DFG source. The saturation spectra of R(18) and R(60) transitions of 00(0)1 <- 00(0)0 fundamental band at 4.2 mu m and P(20) transition of [10(0)1; 02(0)1](I) <- 00(0)0 band at 2.7 mu m have been observed and their absolute transition frequencies are measured with an accuracy better than 30 kHz. (C) 2013 Optical Society of America