Leland Stanford Junior University

Jay B Jeffries

Ronald K Hanson

Michael Evan Webber

Kai Sun

Xing Chao

Ritobrata Sur

A method of calibration-free scanned-wavelength modulation spectroscopy (WMS) absorption sensing is provided by obtaining absorption lineshape measurements of a gas sample on a sensor using 1f-normalized WMS-2f where an injection current to an injection current-tunable diode laser (TDL) is modulated at a frequency f, where a wavelength modulation and an intensity modulation of the TDL are simultaneously generated, extracting using a numerical lock-in program and a low-pass filter appropriate band-width WMS-nf (n=1, 2, . . . ) signals, where the WMS-nf signals are harmonics of the f, determining a physical property of the gas sample according to ratios of the WMS-nf signals, determining the zero-absorption background using scanned-wavelength WMS, and determining non-absorption losses using at least two of the harmonics, where a need for a non-absorption baseline measurement is removed from measurements in environments where collision broadening has blended transition linewidths, where calibration free WMS measurements without knowledge of the transition linewidth is enabled.

Method for calibration-free scanned-wavelength modulation spectroscopy for gas sensing

A system and method utilizing a radiation source with a wavelength near 2 &mgr;m (preferably 1993 nm) to measure the presence of ammonia, carbon dioxide and water vapor using spectroscopic techniques and a reduced measurement pressure is provided. Using radiation substantially near 2 &mgr;m enables one to interrogate the P (3) ammonia transition at a frequency of 5016.977 cm , which is isolated from water and carbon dioxide interference; the P(32) carbon dioxide transition at 5017.030 cm , which is isolated from both ammonia and water interference, and a water transition at 5017.100 cm . Moreover, a tunable radiation source that can sweep over the aforementioned ammonia and carbon dioxide and water features can measure the concentrations of all three species simultaneously. Using a sub-atmospheric pressure substantially near 100 Torr decreases the pressure broadening of different spectroscopic transitions, thereby isolating different absorption features, enabling species-specific measurements without interference, yet retaining sufficient peak absorption.

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Palo Alto, CA, United States of America

Jay B Jeffries