The common hydrocarbon gases and vapors within cell highly absorb {HEAD ~ 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 {TAIL ~ vapors} 
The common hydrocarbon gases and vapors within cell highly absorb { HEAD ~ 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 { TAIL ~ vapors }
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