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