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