Gaseous species absorption monitor
First Claim
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1. A wavelength-locked laser gaseous species monitor, comprising:
- variable wavelength laser means for providing a laser output;
means for adjusting the central wavelength of said laser output to a first laser wavelength at or near a first absorption wavelength of a species being monitored;
means for modulating said laser output about said first laser wavelength to establish a first modulated output having a first modulation frequency and a first modulation bandwidth and a second modulated output having said first modulation frequency and a second modulation bandwidth;
means for providing said first and second modulated outputs to a sample being monitored;
means for collecting at least some of said modulated outputs transmitted through said sample;
means for determining an even harmonic of the collected outputs with respect to said first modulation frequency;
means, responsive to said means for determining, for detecting from said even harmonic of said fist or said second modulated outputs the presence in said sample of said species being monitored; and
means for resolving the concentration of the species being monitored by comparing said even harmonics of said collected outputs.
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Abstract
A wavelength-locked laser gaseous species monitor including a variable wavelength laser with a laser output actively stabilized to a wavelength at or near an absorption wavelength of the species being monitored. The laser is modulated about that wavelength to establish a modulated output with a known frequency and bandwidth. The modulated output is passed through the sample being monitored and then collected. An even harmonic of the collected output with respect to the modulation frequency is determined, and the presence in the sample of the species being monitored is detected from the even harmonic signal.
80 Citations
24 Claims
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1. A wavelength-locked laser gaseous species monitor, comprising:
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variable wavelength laser means for providing a laser output; means for adjusting the central wavelength of said laser output to a first laser wavelength at or near a first absorption wavelength of a species being monitored; means for modulating said laser output about said first laser wavelength to establish a first modulated output having a first modulation frequency and a first modulation bandwidth and a second modulated output having said first modulation frequency and a second modulation bandwidth; means for providing said first and second modulated outputs to a sample being monitored; means for collecting at least some of said modulated outputs transmitted through said sample; means for determining an even harmonic of the collected outputs with respect to said first modulation frequency; means, responsive to said means for determining, for detecting from said even harmonic of said fist or said second modulated outputs the presence in said sample of said species being monitored; and means for resolving the concentration of the species being monitored by comparing said even harmonics of said collected outputs. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A wavelength-locked laser gaseous species monitor, comprising:
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variable wavelength laser means for providing a laser output; means for adjusting the central wavelength of said laser output alternately to a first laser wavelength at or near a first absorption wavelength of a species being monitored, and to a second laser wavelength at or near a second absorption wavelength of the species being monitored; means for alternatively modulating said laser output about said first laser wavelength to establish a first modulated laser output having a first modulation frequency and first modulation bandwidth, and about said second laser wavelength to establish a second modulated laser output having said first modulation frequency and said first modulation bandwidth; means for alternately providing said first and second modulated laser outputs to a sample being monitored; means for collecting at least some of said modulated outputs transmitted through said sample; means for determining an even harmonic of the collected outputs with respect to said first modulation frequency; and means, responsive to said means for determining, for resolving the temperature of the sample being monitored by comparing the even harmonics of the collected outputs from said first and second modulated outputs. - View Dependent Claims (21)
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22. A wavelength-locked laser gaseous species concentration monitor, comprising:
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a variable wavelength semiconductor diode laser for providing a laser output; means for supplying a drive current to said laser; means for regulating the temperature of said laser; means for driving said laser output to match the central wavelength of an absorption line of the species being monitored, said means for driving including; means for modulating said laser output about a wavelength at or near said central wavelength at a known modulation frequency and bandwidth; a reference cell containing the species being monitored; means for passing said modulated laser output through said reference cell; means for collecting at least some of said laser output transmitted through said reference cell; means for determining the third harmonic of the collected reference cell output with respect to the modulation frequency; and means responsive to said means for determining said third harmonic, for adjusting said laser drive current to adjust the laser output wavelength toward said central wavelength; means for passing said modulated laser output through a gas sample being monitored; means for collecting at least some of the laser output transmitted through said sample; means for determining the second harmonic of the collected output from said sample with respect to the modulation frequency; and means, responsive to said second harmonic, for determining the concentration of the species in said sample.
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23. A wavelength-locked laser gaseous species absorption monitor comprising:
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variable wavelength laser means for providing a laser output; means for modulating said laser output about a central wavelength; means for providing said modulated output to a sample being monitored and a reference volume containing the gaseous species being monitored; means for collecting at least some of said modulated output transmitted through said sample and said reference volume; means, responsive to said means for collecting and said means for modulating, for determining the third harmonic of the output collected from the reference volume; means, responsive to said means for determining the third harmonic, for adjusting said central laser wavelength to decrease the absolute value of said third harmonic for locking said central wavelength on the center of an absorption line of the species being monitored; means, responsive to said means for collecting and said means for modulating, for determining an even harmonic of the output collected from said sample; and means, responsive to said means for determining an even harmonic, for detecting from said even harmonic the presence in said sample of said species being monitored.
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24. A wavelength-locked laser gaseous species monitor, comprising:
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variable wavelength laser means for providing a laser output; means for adjusting the central wavelength of said laser output alternately to a first laser wavelength at or near a first absorption wavelength of a species being monitored, and to a second laser wavelength at or near a second adsorption wavelength of the species being monitored; means for alternately modulating said laser output about said first laser wavelength to establish a first modulated laser output having a first modulation frequency and first modulation bandwidth, and about said second laser wavelength to establish a second modulated laser output having said first modulation frequency and said first modulation bandwidth; means for alternately providing said first and second modulated laser outputs to a sample being monitored; means for collecting at least some of said modulated outputs transmitted through said sample; means for determining an even harmonic of the collected outputs with respect to said first modulation frequency; means, responsive to said means for determining, for resolving the temperature of the sample being monitored by comparing the even harmonics of the collected outputs from said first and second modulated outputs; and means, responsive to said means for determining, for detecting from at least one of said even harmonies the presence in said sample of said species being monitored.
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Specification