This paper describes the design and performance of a tunable diode laser system, incorporating a multipass absorption cell to allow determination of water concentration below 10 ppb and carbon dioxide concentration below 1 ppb in nitrogen semiconductor gas. The cell is used with a tunable Pb-salt diode laser spectrometer frequency locked to a first derivative error signal from an intense vibration—rotation molecular absorption line. Sample concentrations are monitored in the second derivative mode, and the system automatically compensates for laser intensity fluctuations. A flowing gas method is used to minimize adsorption/desorption effects from the sample cell walls.
© 1989 Optical Society of America
Ronald D. Schaeffer, J. C. Sproul, J. O’Connell, C. van Vloten, and Arlan W. Mantz, "Multipass absorption cell designed for high temperature UHV operation," Appl. Opt. 28, 1710-1713 (1989)