The common hydrocarbon gases and {HEAD ~ vapors} within {TAIL ~ cell} highly absorb the infrared energy emitted by laser thereby producing an acoustic disturbance which is detected by a transducer which produces an electrical output signal proportional to the concentration of the hydrocarbon gases and vapors 
within
The common hydrocarbon gases and { HEAD ~ vapors } within { TAIL ~ cell } highly absorb the infrared energy emitted by laser thereby producing an acoustic disturbance which is detected by a transducer which produces an electrical output signal proportional to the concentration of the hydrocarbon gases and vapors
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