Tunable Quantum Cascade Lasers and Photoacoustic Detection of Trace Gases, TNT, TATP and Precursors Acetone and Hydrogen Peroxide
First Claim
1. A method for more quickly determining the presence of a target gas, the steps comprising:
- 1) Identifying and selecting regions in a frequency range of a selectable wavelength light source which meets all the following criteria;
a) the target gas has large absorption in at least some frequencies in said frequency range;
b) expected interferents have low absorption at their expected concentrations; and
c) a detectable signature of target gas is linearly independent of signature of interferents;
2) collecting a sample of gas for testing of the target gas;
3) Perform a scan across said identified and selected regions and collecting photoacoustic data from said scan; and
4) Linearly deconvolving said photoacoustic data against a standardized library of the target gas and list of expected interferents, to obtain a gas concentration measurement for the target gas.
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Abstract
Methods and apparatus for broad tuning of single wavelength quantum cascade lasers and the use of light output from such lasers for highly sensitive detection of trace gases such as nitrogen dioxide, acetylene, and vapors of explosives such as trinitrotoluene (TNT) and triacetone triperoxide (TATP) and TATP'"'"'s precursors including acetone and hydrogen peroxide. These methods and apparatus are also suitable for high sensitivity, high selectivity detection of other chemical compounds including chemical warfare agents and toxic industrial chemicals. A quantum cascade laser (QCL) system that better achieves single mode, continuous, mode-hop free tuning for use in L-PAS (laser photoacoustic spectroscopy) by independently coordinating gain chip current, diffraction grating angle and external cavity length is described. An all mechanical method that achieves similar performance is also described. Additionally, methods for improving the sensor performance by critical selection of wavelengths are presented.
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Citations
13 Claims
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1. A method for more quickly determining the presence of a target gas, the steps comprising:
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1) Identifying and selecting regions in a frequency range of a selectable wavelength light source which meets all the following criteria; a) the target gas has large absorption in at least some frequencies in said frequency range; b) expected interferents have low absorption at their expected concentrations; and c) a detectable signature of target gas is linearly independent of signature of interferents; 2) collecting a sample of gas for testing of the target gas; 3) Perform a scan across said identified and selected regions and collecting photoacoustic data from said scan; and 4) Linearly deconvolving said photoacoustic data against a standardized library of the target gas and list of expected interferents, to obtain a gas concentration measurement for the target gas. - View Dependent Claims (2, 3, 4, 5)
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6. A target gas detection system, comprising:
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a continuously-tunable laser operating at room temperature and tuned for exciting a sample of target molecules among other interferents; and an L-PAS cell receiving light from said laser and containing gas to be sampled and tested for said target molecules;
wherebydetection of said target molecules can be made despite presence of interferent signals. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13)
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Specification