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