Design and operation of a compact, portable, room-temperature mid-infrared gas sensor is reported. The sensor is based on continuous-wave difference-frequency generation (DFG) in bulk periodically poled lithium niobate at 4.6 mum, pumped by a solitary GaAlAs diode laser at 865 nm and a diode-pumped monolithic ring Nd:YAG laser at 1064.5 nm. The instrument was used for detection of CO in air at atmospheric pressure with 1 ppb precision (parts in 10(9), by mole fraction) and 0.6% accuracy for a signal averaging time of 10 s. It employed a compact multipass absorption cell with a 18-m path length and a thermoelectrically cooled HgCdTe detector. Precision was limited by residual interference fringes arising from scattering in the multipass cell. This is the first demonstration of a portable high-precision gas sensor based on diode-pumped DFG at room temperature. The use of an external-cavity diode laser can provide a tuning range of 700 cm(-1) and allow the detection of several trace gases, including N(2) O, CO(2), SO(2), H(2) CO, and CH(4).
Detection of CO, N(2)O, and CO(2) in ambient air was performed with a room-temperature cw IR source based on difference-frequency generation in periodically poled LiNbO(3). The source was pumped by a seeded highpower GaAlAs amplif ier at 860 nm and a diode-pumped monolithic Nd:YAG ring laser at 1064 nm. The IR output was tunable between 2160 and 2320 cm(-1) without crystal rotation. The CO detection sensitivity is extrapolated to 5 ppb m/ radicalHz if limited by IR intensity noise.
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