wherein the second portion of the focused laser beam reflected back to {TAIL ~ the focusing lens} is converted into {HEAD ~ a return laser beam} by the focusing lens, and 
wherein the second portion of the focused laser beam reflected back to { TAIL ~ the focusing lens } is converted into { HEAD ~ a return laser beam } by the focusing lens , and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH