{HEAD ~ A system} employing the optical element may include a light source and {TAIL ~ a detector} 
include
{ HEAD ~ A system } employing the optical element may include a light source and { TAIL ~ a detector }
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL