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