A system 1, wherein the system comprises a phase locked loop for measuring {HEAD ~ the amplitude} of {TAIL ~ a photoacoustic signal} 
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A system 1 , wherein the system comprises a phase locked loop for measuring { HEAD ~ the amplitude } of { TAIL ~ a photoacoustic signal }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL