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