A scraper mirror reflects the beams to a thermal imager which reflects {HEAD ~ the beams} to {TAIL ~ a pair} of NaCl beamsplitters 
to
A scraper mirror reflects the beams to a thermal imager which reflects { HEAD ~ the beams } to { TAIL ~ a pair } of NaCl beamsplitters
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH