{HEAD ~ The returned beam} is focused to the optical disc via the optical member and {TAIL ~ the beam splitter} 
is focused via
{ HEAD ~ The returned beam } is focused to the optical disc via the optical member and { TAIL ~ the beam splitter }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH REL OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL