Diagnostic tests using near-infrared laser absorption spectrosco

Details Diagnostic tests using near-infrared laser absorption spectrosco Diagnostic tests using near-infrared laser absorption spectrosco

1992-01-29

1994-05-31

Fields, Carolyn E.

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

25033911, 250346, 250350, 250351, G01N 2135

Patent

active

053171560

ABSTRACT:
RF modulation spectroscopy of a near infrared laser diode source is used to determine the amount of a target substance in a breath sample. In this type of modulation the laser output is modulated to produce sidebands displaced from the laser carrier by the modulation frequency. The modulated beam is passed through a gas sample which differentially absorbs the sidebands, the result of which is the conversion of some of the laser frequency modulation into amplitude modulation which is subsequently detected using a broadband photodetector. In certain tests, the target substance is a particular isotope, whose concentration is measured as an isotope ratio. In order to measure the presence of first and second isotopic species, provision is made to provide laser illumination at characteristic wavelengths for absorption lines for the first and second isotopic species of the gas. This may sometimes be accomplished using a single laser diode and scanning at least one of its operating parameters in order to achieve one of the wavelength difference. Alternatively, first and second laser diodes operating at the first and second wavelengths are used.

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C. S. Irving et al., "Measurements of .sup.13 CO.sub.2 /.sup.12 CO.sub.2 Abundance by Nondispersive Infrared Heterodyne Ratiometry as an Alternative to Gas Isotope Ratio Mass Spectrometry", Analytical Chemistry, Sep. 1986, vol. 58, No. 11, pp. 2172-2178.
P. S. Lee et al., "Tunable Diode Laser Spectroscopy for Isotope Analysis-Detection of Isotopic Carbon Monoxide in Exhaled Breath", IEEE Transactions on Biomedical Engineering, Oct. 1991, vol. 38, No. 10, pp. 966-973.
Abstract of Japanese Patent Publication No. JP4042041, Published May 21, 1992, Abstract vol. 016218.

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