dichroic means for reflecting said first beam in a third direction and for transmitting said second beam therewith whereby {HEAD ~ said second beam} follows {TAIL ~ said first beam} 
dichroic means for reflecting said first beam in a third direction and for transmitting said second beam therewith whereby { HEAD ~ said second beam } follows { TAIL ~ said first beam }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL