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