A new technique is presented for obtaining gas concentration by measuring the slope of the anomalous dispersion at a resonance. We describe the equations that govern this process using a Lorentz model and show that the slope of the anomalous dispersion is directly related to the absorption coefficient. The slope is obtained from an interferometric setup and a frequency modulation spectroscopy technique. Experimental data are presented that illustrate this technique for two different sample cells containing water vapor.
© 1998 Optical Society of America
(060.2630) Fiber optics and optical communications : Frequency modulation
(120.0120) Instrumentation, measurement, and metrology : Instrumentation, measurement, and metrology
(120.3940) Instrumentation, measurement, and metrology : Metrology
Craig R. Schwarze, Julie A. Gargas, Julia H. Rentz, and Michael Hercher, "Method for Obtaining Gas Concentration with a Phase-Based Metrology System," Appl. Opt. 37, 3942-3947 (1998)