Cavity enhanced laser based isotopic gas analyzer
Inventors
Koulikov, Serguei • Kachanov, Alexander
Assignees
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Publication Number
US-9678003-B2
Publication Date
2017-06-13
Expiration Date
Abstract
Systems and methods for measuring the isotope ratio of one or more trace gases and/or components of gas mixtures such as different gas species present in a gas mixture. The system includes a resonant optical cavity having two or more mirrors and containing a gas, the cavity having a free spectral range that equals the difference between frequencies of two measured absorption lines of different gas species in the gas, or of two different isotopes, divided onto an integer number. The system also includes a continuous-wave tunable laser optically coupled with the resonant optical cavity, and a detector system for measuring an absorption of laser light by the gas in the cavity. The detector system includes one of a photo-detector configured to measure an intensity of the intra-cavity light or both a photo-acoustic sensor configured to measure photo-acoustic waves generated in the cavity and a photo-detector configured to measure an intensity of the intra-cavity light.
Core Innovation
The invention relates to a gas analyzer system using a resonant optical cavity having two or more mirrors and a set cavity length, where a free spectral range equals the difference between frequencies of two predetermined or known absorption lines of two different gas species to be measured divided onto an integer number. A continuous-wave tunable laser is optically coupled to the resonant optical cavity, and a detector system measures absorption of laser light by the gas in the cavity at the two predetermined or known absorption lines.
The invention also relates to a gas analyzer system for measuring an isotopic ratio of a gas species, using the same resonant optical cavity concept with the free spectral range set by the difference between frequencies of two predetermined or known absorption lines of two different isotopes divided onto an integer number. The continuous-wave tunable laser is tuned to a first wavelength corresponding to an absorption line of a first isotope and to a second wavelength corresponding to an absorption line of a second isotope, and the detector system measures a first signal and a second signal corresponding to absorption at the respective wavelengths.
The system further incorporates detector functionality and signal processing approaches to support isotopic and trace gas analysis, including measuring absorption using intracavity light intensity via a photo-detector and measuring absorption-related signals using photo-acoustic waves via a photo-acoustic sensor. Temperature and pressure sensing are included, and the intelligence module uses the measured signals to determine isotope ratios or concentrations.
Claims Coverage
The document provides three independent claims, each built around a resonant optical cavity with a free spectral range matched to a frequency difference, a continuous-wave tunable laser tuned to two predetermined absorption lines, detector measurement at those absorption lines, and an intelligence module that processes first and second detector signals to generate an output.
Matched free spectral range to absorption-line frequency difference
A resonant optical cavity having two or more mirrors with a set cavity length and a free spectral range that equals the difference between frequencies of two predetermined or known absorption lines divided onto an integer number.
Continuous-wave tunable laser tuned to two predetermined absorption lines
A continuous-wave tunable laser optically coupled with the resonant optical cavity, tuned to a first wavelength corresponding to a predetermined or known absorption line and to a second wavelength corresponding to a predetermined or known absorption line.
Detector measurement of absorption at two predetermined absorption lines
A detector system for measuring absorption of laser light by the gas in the cavity at the two predetermined or known absorption lines, producing a first signal and a second signal corresponding to absorption at the respective wavelengths.
Processor processes two detector signals to generate output
An intelligence module comprising a processor adapted to process the first and second signals and generate an output signal representing concentrations of gas species, an isotope ratio, or concentrations of isotopes.
Across the independent claims, the core inventive structure is a resonant optical cavity with a free spectral range matched to a frequency difference between two predetermined absorption lines, a continuous-wave tunable laser tuned to two such wavelengths, detector measurement of absorption at those wavelengths, and an intelligence module processor that processes the first and second detector signals to generate an output.
Stated Advantages
Accurate isotope ratio measurement by using a resonant optical cavity and wavelength tuning to predetermined absorption lines with a free spectral range matched to the frequency difference.
Simplifying intensity measurements using peak-intensity approaches for isotopic lines with similar temperature/pressure dependencies.
Optional use of baseline measurements at non-absorbing wavelengths to support signal processing for isotope ratio or concentration determination.
Incorporation of temperature and pressure sensing for measuring gas conditions used alongside the detector signals.
Documented Applications
Measuring concentrations of two or more gas species in a gas mixture using cavity-enhanced laser-based absorption at two predetermined absorption lines.
Measuring an isotopic ratio of a gas species using a resonant optical cavity tuned to two isotopic absorption lines.
Measuring concentrations of isotopes in a gas species using cavity-enhanced absorption at two isotopic absorption lines.
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