The second mirror is configured to receive 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 {HEAD ~ a fourth reflected beam} from {TAIL ~ the fourth mirror} 
The second mirror is configured to receive 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 { HEAD ~ a fourth reflected beam } from { TAIL ~ the fourth mirror }
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 OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL