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