An incoherent light beam is directed into {HEAD ~ one surface} of {TAIL ~ an optical wedge device} 
of
An incoherent light beam is directed into { HEAD ~ one surface } of { TAIL ~ an optical wedge device }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL