A widely tunable difference-frequency-generation laser for high-resolution spectroscopy in the 667–865 cm–1 range

Mid-infrared (MIR) laser sources are used in a number of applications such as remote sensing, air pollution monitoring, combustion diagnostics, and molecular spectroscopy. Here, we present our work on the development of a MIR laser source based on the difference frequency generation (DFG) process between an external-cavity quantum-cascade-laser tunable over 1750–1835 cm^–1 (pump source) and a CO₂ gas laser tunable over 921–1083 cm^–1 (signal source). The DFG process was realized in a nonlinear, orientation-patterned GaAs crystal, and resulted in an idler spectral range between 667–865 cm^–1 with a linewidth of ~2.3 MHz and an output power of up to ~31 μW. Exploiting the fine tunability of our DFG laser source, we performed high-resolution absorption measurements of ethylene (C₂H₄) and acetylene (C₂H₂).