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