{HEAD ~ Some part} of {TAIL ~ the incident laser beam} is reflected by the optical member and then returned to the beam splitter to be focused on an optical disc 
of
{ HEAD ~ Some part } of { TAIL ~ the incident laser beam } is reflected by the optical member and then returned to the beam splitter to be focused on an optical disc
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH