Physical Sciences Inc. Publications Abstract: Widely tunable rapid-scanning mid-infrared laser spectrometer for industrial gas process stream analysis

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Abstract: Widely tunable rapid-scanning mid-infrared laser spectrometer for industrial gas process stream analysis

Douglas J. Bamford, David J. Cook, Scott J. Sharpe, Aaron D. Van Pelt, "Widely tunable rapid-scanning mid-infrared laser spectrometer for industrial gas process stream analysis ," Applied Optics: Laser Applications to Chemical, Security and Enviromental Analysis 2006 46 (19) , 3958-3968 (July2007).

Reprinted by permission of the Optical Society of America. For permission to copy or republish, contact the Optical Society of America, 2010 Massachusetts Ave. NW, Washington, DC 20036-1023.

Abstract

A mid-infrared spectrometer with a tuning range of >400 cm^-1 in the C–H stretching region of the spectrum has been designed and constructed. The spectrometer is based on the difference-frequency generation of two tunable diode lasers in periodically poled lithium niobate waveguides. Tuning is achieved by varying a single parameter, the wavelength of one of the near-infrared input lasers. The instrument can be tuned over the entire tuning range in less than 1 s. By taking advantage of the wide tuning range, the instrument has been used to analyze a mixture of methane, ethylene, and propylene. Each of these major components was measured with an accuracy of better than 2% (where the error is defined as a percentage of the measured value) in a single 30 s long scan. When optimized, the spectrometer has the potential to meet both the performance requirements and the practical requirements for real-time process control in petrochemical manufacturing. The general principles for the design of mid-infrared spectrometers with wide tuning ranges are explained, including the use of variable waveguide fabrication recipes to create broad phase matching resonances (which lead to broad tuning) in the desired location.

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