Tunable diode laser absorption spectroscopy with water vapor determination

Abstract

A gas absorption spectroscopy system and method are provided. A sealed chamber is provided with a reference gas having a known moisture concentration. An illumination source is disposed in the sealed chamber and is configured to generate an illumination beam. A measurement cell is coupled to the sealed chamber and is configured for exposure to a gas sample such that illumination travelling through the measurement cell passes through the gas sample. A process window is disposed between the sealed chamber and the measurement cell. The process window is configured to receive the illumination beam from the illumination source and reflect a first portion of illumination while allowing a second portion of illumination to pass into the measurement cell. A reference detector is disposed to receive the first portion of illumination and provide a reference detector signal. A measurement detector is disposed to receive the second portion of illumination after the second portion of illumination has passed through the measurement cell and provide a measurement detector signal. A controller is coupled to the reference detector and the measurement detector and is configured to provide a compensated moisture output based on the reference detector signal and the measurement detector signal.

Description

Background technique [0001] Gas absorption spectroscopy typically measures the presence and / or concentration of a species of interest in a gas sample by transmitting a beam of light through the sample and detecting absorption at wavelengths of a specific spectral absorption signature of the species of interest. Typically, the feature is an absorption line representing the frequency of light corresponding to a vibrational, rotational or electronic transition of the molecules of the gas of interest. Tunable diode lasers offer many advantages for such gas absorption spectroscopy measurements in that the laser can be tuned to the center of the spectral feature and generate a narrowband signal about the width of the spectral feature. [0002] Thus, laser absorption spectroscopy can provide high-speed and relatively high-precision capabilities for the detection of various trace gas species in gas samples at atmospheric pressure with relatively low cross-sensitivity to other gas spec...

AI Technical Summary

Problems solved by technology

Another important limitation in the detection of trace moisture content in gas samples is that laser noise and optical noise induced near the laser beam delivery optics can also limit the sensitivity and precision of the spectrometer

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