A second laser, a cw CO2 laser, has {HEAD ~ its beam} transmitted through {TAIL ~ the dichroic} to follow the HeNe beam into the unstable resonator laser aperture 
transmitted through
A second laser , a cw CO2 laser , has { HEAD ~ its beam } transmitted through { TAIL ~ the dichroic } to follow the HeNe beam into the unstable resonator laser aperture
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH