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