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