초록 ▼

An apparatus and method are disclosed for measuring the concentration of gases that are unstable or difficult contain in a sample cell. A frequency modulated laser is tuned to the frequency of a first spectral feature of a gas of interest and a laser beam is projected through a reference cell contai

An apparatus and method are disclosed for measuring the concentration of gases that are unstable or difficult contain in a sample cell. A frequency modulated laser is tuned to the frequency of a first spectral feature of a gas of interest and a laser beam is projected through a reference cell containing, at a selected pressure, a selected second gas that has a second spectral feature near the first spectral feature of the gas of interest. The laser is line-locked to an outer zero crossing of a third harmonic of the detected laser beam coincident with the first spectral feature. The concentration of the gas of interest is calculated from a second harmonic of a portion of the laser beam projected through a transmission medium containing the gas.

대표청구항 ▼

[ What is claimed is:] [1.] Apparatus for measuring concentration of a sample gas in a transmission medium comprising:a laser projecting a laser beam, said laser beam being tuned to a frequency corresponding to a spectral feature of said sample gas and, said laser beam being frequency modulated at a

[ What is claimed is:] [1.] Apparatus for measuring concentration of a sample gas in a transmission medium comprising:a laser projecting a laser beam, said laser beam being tuned to a frequency corresponding to a spectral feature of said sample gas and, said laser beam being frequency modulated at a selected modulation amplitude;a beamsplitter that splits said laser beam into a first beam portion and a beam second portion;a reference cell containing a selected reference gas at a selected pressure;a first detector, said first beam portion being projected from said beamsplitter through said reference cell to said first detector, said first detector measuring an intensity of said first beam portion and producing an electrical first signal proportional to said intensity of said first beam portion;a second detector, said second beam portion being projected from said beamsplitter through the transmission medium to said second detector, said second detector measuring an intensity of said second beam portion and producing an electrical second signal proportional to said intensity of said second beam portion;a controller that receives said first signal from said first detector and said second signal from second detector, said controller separating said first signal into harmonics including a line-locked harmonic and separating said second signal into harmonics including a second harmonic;said reference gas being selected such that said reference gas has a spectral feature near said spectral feature of said sample gas;said reference gas, said selected pressure of said reference gas, and said modulation amplitude being selected such that an outer zero crossing of said line-locked harmonic of said first signal is coincident with said frequency of said laser beam; andsaid controller controlling said laser and monitoring said line-locked harmonic to line-lock said laser beam at said outer zero crossing, said controller monitoring said second harmonic of said second signal to calculate concentration of said sample gas.