Boc Health Care, Inc.

Albion Instruments, Inc.

John R Mitchell

Donald E Gregonis

Scott D Miles

Kent F Beck

Joel M Harris

Joseph W Carter

A method and apparatus for determining the composition and concentration of gases present in a gas sample by measurement of the spectrum of Raman scattered light from these gases. A diode laser illuminates the unknown gas which is contained inside a long hollow tube having a highly reflective interior wall. A laser line pass filter at an entrance aperture of the hollow tube prevents all wavelengths except specific wavelengths characteristic of the laser from entering the long hollow tube. The laser beam and Raman scattered light from the gas sample reflect inside the hollow tube from the highly reflective interior wall. A laser line rejection filter at an exit aperture of the hollow tube prevents the laser beam from exiting the hollow tube but transmits the Raman scattered light from the gas sample. A spectrograph detector or array of discrete filters and detectors detects the Raman scattered light. The output of the detector(s) is then analyzed to identify the constituents of the unknown gas sample and the concentrations of the constituents.

Diode laser pumped Raman gas analysis system with reflective hollow tube

A Raman spectroscopy system and method for determining a zero-calibration level. A gas sample chamber is located within a resonant cavity. A light source is located to cause light to be incident on the gas sample, the light resonates in the resonant cavity. Typically, the light source and resonator cavity in conjunction form a laser source which propagates coherent, monochromatic laser light energy through the gas sample. This causes Raman scattering from the gases constituent in the gas sample. The amount of Raman scattered light is measured at detectors along with light due to dark noise inherent in the detectors and glow from the laser source, i.e., light at wavelengths other than the laser light wavelength produced by the laser source. The resonator cavity is obstructed, via a ball inserted into the path of the laser beam for example, to prevent resonance. If the light source and resonant cavity in conjunction form a laser, prevention of resonance causes cessation of lasing. Thus, substantially no Raman scattering occurs and detectors measure light due primarily to background noise. The origin of the measurement scale for the detectors may then be set at the measured intensity, i.e., a zero-calibration level for the detectors may be determined.

Method and apparatus for zero-calibration of a raman spectroscopy system

A gas analysis cell having a pressure control system eliminates pressure variations in the gas cell regardless of changes in restriction, gas viscosity and barometric pressure. Since optical alignment through the gas cell is sensitive to gas pressure, maintaining a constant pressure in the gas cell makes the system more stable.

Constant pressure gas cell

A gas analysis cell positioned within an optical resonant cavity in a gas analysis system is disclosed wherein the cell includes a flow of buffer gas which forms a 'dam', thereby protecting the optical elements in the analysis system. The analysis cell includes an inlet for introducing a gas sample into the analysis chamber of the cell. Two buffer gas inlet ports, one on each end of the cell, are provided to introduce a flow of buffer gas which is directed past optical elements in the system adjacent the ends of the cell. Two output ports are located at the ends of the analysis chamber to remove the buffer gas and gas sample mixture. The flow of buffer gas acts to confirm the gas sample within the analysis chamber and reduce adverse effects which occur when the gas sample comes in contact with the optical elements of the system. By providing a constant non-turbulent flow of gas adjacent the system optics, adverse changes in index of refraction are avoided, thus reducing beam steering and Schlieren effects which can occur when Brewster windows or other optics are used to constrain the gas sample within the analysis cell. The buffer gas flow in the analysis cell of the present invention eliminates the need for gas cell windows which have intrinsic losses. This in turn minimizes losses which cause lower circulating intracavity power and signal strength.

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Salt Lake City, UT, United States of America

John R Mitchell