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