Gas detector
AssigneeEnvironmental Research & Technology, Inc.
InventorPaul L. Kebabian
Life of this patent
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Abstract
A methane detector comprising a He-Ne laser in which the plasma tube forms a portion of the resonant cavity and the laser can be stimulated to emit at two different atomic resonances at separate wave numbers .nu..sub.1 and .nu..sub.2, one of which is more strongly absorbed by methane than the other. Means such as a beam splitter disposed in the resonant cavity, are provided for directing two beams outwardly from the cavity to a pair of detectors each provided in the path of a respective beam. The cavity is tuned so that its length L meets the criterion m/2L = .nu..sub.1 -.nu..sub.2, m being a number of half integers. Means are provided for cyclically varying the gain of the laser across one free spectral range through some tuned center value.
Claims20
A device for detecting the presence of a specific gas in an atmosphere to be tested, said device comprising, in combination:
- a laser having a resonant cavity at least a portion of which contains a material in which emission can be stimulated at least at two different frequencies centered at wave numbers separated by some difference .DELTA..nu., the emission at one of said frequencies being more strongly absorbed by said gas that the emission at the other of said frequencies, said material and cavity being selected so that the gain of said laser is normally higher for emission at said one frequency that at said other frequency, said cavity being tuned so that
- m/2L = .DELTA..nu.
- where L is the optical length of the cavity and m is a number of half integers,
- means for directing at least part of the stimulated emission outwardly from said cavity, first detector means positioned for irradiation by said part of said emission for producing electrical signals responsively to emissions at least at said other frequency;
- and
- means for cyclically varying the tuning of said laser through at least a free spectral range.
Dependencies are inferred from the claim text.