Difference Frequency Generation Based Mid-infrared System for High Sensitive Detection of Atmospheric Gas

Room-temperature continuous-wave tunable narrow band coherent light sources emitting in the mid-infrared region are valuable for trace gas sensing techniques. Nonlinear optical difference-frequency generation (DFG) scheme is a useful way to meet the requirement, and a kind of good complementarity for traditional laser technology. The basic principle of quasi-phase-matching (QPM) of DFG is depicted, the temperature tuning characteristics of periodically poled LiNbO3(PPLN) are studied based on the Sellmeier equation for the extraordinary refraction index. Setting the CH2O as target gas, a DFG based mid-infrared spectroscopic detection system is described. A telecommunication distributed-feedback(DFB) diode laser and a high power Yb fiber laser are used as signal and pump sources to generate 3.53μm coherent light. The characteristics of this system are room-temperature, all fiber-coupled and compact. This system can meet the demands of high sensitive detection of atmospheric trace gases.