Modulation cancellation method in laser spectroscopy
First Claim
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1. A method of measuring a concentration of a first and a second compound in a sample composition comprising:
- a) providing at least first and second modulated light beams having first and second wavelengths, respectively, wherein the modulation of the second modulated light beam is phase shifted from the modulation of the first modulated light beam;
b) passing the first and the second modulated light beams through a reference composition, wherein said reference composition comprises a reference concentration of the first and the second compound;
c) detecting a reference signal resulting from the absorption of the first and second modulated light beams by the reference composition;
d) adjusting the amplitude of the second modulated light beam such that no reference signal is detected;
e) passing the first modulated light beam and the second modulated light beam through a sample composition; and
f) detecting a sample signal so as to measure the concentration of the first and the second compound in the sample composition.
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Abstract
Novel methods and laser spectroscopic systems for accurately measuring the concentration of compounds are disclosed herein. The disclosed methods utilize a modulation cancellation technique resulting in a significantly increase in the sensitivity and accuracy of laser spectroscopic measurements. In general, the methods and systems utilize modulation phase-shifting and amplitude attenuation to cancel the signals detected from at least two modulated light beams. Thus, any signal detected will be directly proportional to the concentration measurement.
19 Citations
32 Claims
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1. A method of measuring a concentration of a first and a second compound in a sample composition comprising:
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a) providing at least first and second modulated light beams having first and second wavelengths, respectively, wherein the modulation of the second modulated light beam is phase shifted from the modulation of the first modulated light beam; b) passing the first and the second modulated light beams through a reference composition, wherein said reference composition comprises a reference concentration of the first and the second compound; c) detecting a reference signal resulting from the absorption of the first and second modulated light beams by the reference composition; d) adjusting the amplitude of the second modulated light beam such that no reference signal is detected; e) passing the first modulated light beam and the second modulated light beam through a sample composition; and f) detecting a sample signal so as to measure the concentration of the first and the second compound in the sample composition. - 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 method for measuring the concentration of a compound having a background wavelength and an absorption wavelength, said method comprising:
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a) providing at least first and second modulated light beams, wherein the modulation of second modulated light beam is phase shifted from the modulation of the first modulated light beam; b) tuning the first modulated light beam to the background wavelength of the compound and the second modulated light beam to the absorption wavelength of the compound; c) tuning the amplitude of the second modulated light beam such that no signal is detected when the first and the second modulated light beams are passed through a composition lacking the compound; d) passing the first and the second modulated light beams through a sample composition; and e) detecting a signal indicative of the concentration of the compound in the sample composition. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A laser spectroscopic system comprising:
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a first and a second light source, wherein said first and said second light source emit first and second modulated light beams, respectively, wherein the modulation of said second modulated light beam is phase shifted from the modulation of said first modulated light beam; a sample cell comprising a sample detector, wherein said sample cell contains a sample composition comprising a first and a second compound, wherein said first and said second modulated light beams pass through said sample cell; a reference cell comprising a reference detector, wherein said reference cell contains a reference concentration of the first and the second compound, wherein said first and said second modulated light beams pass through said reference cell; and an attenuator coupled to said reference detector and said second light source, wherein said attenuator controls the second light source to match the amplitude of the second modulated light beam to the amplitude of the first modulated light beam such that no signal is detected from the reference detector. - View Dependent Claims (31, 32)
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Specification