{HEAD ~ The common hydrocarbon gases} and 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
{ HEAD ~ The common hydrocarbon gases } and 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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