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