Compact laser difference-frequency spectrometer for multicomponent trace gas detection

Design, performance characteristics, and application of a room temperature mid-infrared laser spectrometer an reported. This compact instrument is based on difference-frequency mixing of a widely tunable external-cavity diode laser and a diode-pumped monolithic Nd:YAG ring laser in periodically poled lithium niobate (PPLN). The difference-frequency tuning range of 3.98 mu m to 4.62 mu m was sufficient for detection of several atmospheric trace gases including carbon monoxide (CO), nitrous oxide (N2O), carbon dioxide (CO2), and sulfur dioxide (SO2). Real-time detection of CO, N2O, and CO2 was performed in open air over a path length of 5 to 18 m. The feasibility of DFG spectroscopic measurement of the C-13/C-12 and O-18/O-17/O-16 isotopic ratios in atmospheric carbon dioxide was also investigated. We report what to our knowledge is the first simultaneous spectroscopic measurement of all three isotopes of oxygen in ambient CO2.