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