Leland Stanford Junior University

Ronald K Hanson

Jay B Jeffries

Jian Jun Wang

Michael Evan Webber

Ritobrata Sur

Xing Chao

Kai Sun

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.

Gas sensor for ammonia, carbon dioxide and water

A method and apparatus for temperature-independent determination of a concentration of a probe gas in a sample over a selected temperature range between a low temperature T corresponding to a lowest temperature expected or found in the sample and a high temperature T corresponding to a highest temperature expected or found in the sample. In accordance with the method, a probe temperature function of the probe gas is determined over the temperature range using a first spectroscopic technique. Then, a second spectroscopic technique is selected, a reference gas is identified and a reference temperature function of the reference gas is determined using the second spectroscopic technique over the temperature range. In particular, the reference gas is identified such that a ratio of the probe temperature function and the reference temperature function is substantially constant over the temperature range. A probe reaction of the probe gas and a reference reaction of the reference gas is then measured by the first and second spectroscopic techniques and the concentration of the probe gas is derived from the probe reaction and reference reaction. The method of the invention can be take advantage of spectroscopic techniques such as absorption spectroscopy employing a test beam of light at several wavelengths with at least one wavelength for either probe transition or reference transition. The method and apparatus can be used in monitoring various gas samples and are especially well-suited for determining probe gas concentrations in samples which exhibit non-uniformities in temperature, pressure and gas composition, e.g., as encountered in vehicle exhaust samples.

Temperature-independent measurements of gas concentration

A system and method for non-intrusively obtaining the thrust value of combustion by-products of a jet engine is disclosed herein. The system includes laser elements for inducing absorption for use in determining the axial velocity and density of the jet flow stream and elements for calculating the thrust value therefrom.

Growing community of inventors

Cupertino, CA, United States of America

Ronald K Hanson