COMPACT LASER DIFFERENCE-FREQUENCY SPECTROMETER FOR MULTICOMPONENT TRACE GAS-DETECTION

Design, performance characteristics, and application of a room tempera ture mid-infrared laser spectrometer an reported. This compact instrum ent is based on difference-frequency mixing of a widely tunable extern al-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 o f several atmospheric trace gases including carbon monoxide (CO), nitr ous oxide (N2O), carbon dioxide (CO2), and sulfur dioxide (SO2). Real- time detection of CO, N2O, and CO2 was performed in open air over a pa th length of 5 to 18 m. The feasibility of DFG spectroscopic measureme nt 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 isoto pes of oxygen in ambient CO2.