title: Widely tunable rapid-scanning mid-infrared laser spectrometer for industrial gas process stream analysis.
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.
authors.affiliation: Physical Sciences, Incorporated, 2110 Omega Road, Suite D, San Ramon, California 94583-1295, USA. bamford@psicorp.com
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Bamford
authors.forename: David J
authors.initials: DJ
authors.lastname: Cook
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Sharpe
authors.forename: Aaron D
authors.initials: AD
authors.lastname: Van Pelt
mesh_terms: D000475:Alkenes / Q000737:chemistry; D002244:Carbon / Q000737:chemistry; D004867:Equipment Design; D005030:Ethylenes / Q000737:chemistry; D005740:Gases; D006859:Hydrogen / Q000737:chemistry; D007834:Lasers; D008697:Methane / Q000737:chemistry; D015233:Models, Statistical; D055095:Optics and Photonics; D012984:Software; D013055:Spectrophotometry, Infrared / Q000295:instrumentation* / Q000379:methods*; D013696:Temperature; D013997:Time Factors
chemical_list: D000475:Alkenes; D005030:Ethylenes; D005740:Gases; D002244:Carbon; D006859:Hydrogen; C036216:ethylene; C013658:propylene; D008697:Methane