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