{HEAD ~ a laser light source} for transmitting {TAIL ~ a laser beam} which is disposed in the housing 
for transmitting
{ HEAD ~ a laser light source } for transmitting { TAIL ~ a laser beam } which is disposed in the housing
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH