{HEAD ~ a detecting means} for receiving and detecting {TAIL ~ beams} which are incident on and reflected by the beam splitter after being reflecting from the optical disc, 
for detecting
{ HEAD ~ a detecting means } for receiving and detecting { TAIL ~ beams } which are incident on and reflected by the beam splitter after being reflecting from the optical disc ,
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH