Both beams are injected into an unstable laser resonator aperture in {HEAD ~ the center} of {TAIL ~ a primary mirror} in the resonator 
Both beams are injected into an unstable laser resonator aperture in { HEAD ~ the center } of { TAIL ~ a primary mirror } in the resonator
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH