A turnable carbon dioxide gas laser produces {HEAD ~ laser beams} and both in {TAIL ~ the infrared region} which are highly absorbed by the propane and n butane component gases, respectively, flowing through photoacoustic cell  
A turnable carbon dioxide gas laser produces { HEAD ~ laser beams } and both in { TAIL ~ the infrared region } which are highly absorbed by the propane and n butane component gases , respectively , flowing through photoacoustic cell
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