{HEAD ~ The second mirror} is configured to receive {TAIL ~ a second incident laser beam} from the second end and reflecting a second reflected beam to intersect the first reflected beam and to reflect as a fourth reflected beam from the fourth mirror 
{ HEAD ~ The second mirror } is configured to receive { TAIL ~ a second incident laser beam } from the second end and reflecting a second reflected beam to intersect the first reflected beam and to reflect as a fourth reflected beam from the fourth mirror
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH