ROOM-TEMPERATURE MIDINFRARED LASER SENSOR FOR TRACE GAS-DETECTION

Design and operation of a compact, portable, room-temperature mid-infr ared gas sensor is reported. The sensor is based on continuous-wave di fference-frequency generation (DFG) in bulk periodically poled lithium niobate at 4.6 mu m, pumped by a solitary GaAlAs diode laser at 865 n m and a diode-pumped monolithic ring Nd:YAG laser at 1064.5 nm. The in strument was used for detection of CO in air at atmospheric pressure w ith 1 ppb precision (parts in 10(9), by mole fraction) and 0.6% accura cy for a signal averaging time of 10 s. It employed a compact multipas s absorption cell with a 18-m path length and a thermoelectrically coo led HgCdTe detector. Precision was limited by residual interference fr inges arising from scattering in the multipass cell. This is the fist demonstration of a portable high-precision gas sensor based on diode-p umped DFG at room temperature. The use of an external-cavity diode las er can provide a tuning range of 700 cm(-1) and allow the detection of several trace gases, including N2O, CO2, SO2, H2CO, and CH4. (C) 1997 Optical Society of America.