{HEAD ~ The generator} comprises {TAIL ~ an envelope} and two mirrors defining a resonant cavity, in which is maintained a monolithic wave guide with a capillary 
comprises
{ HEAD ~ The generator } comprises { TAIL ~ an envelope } and two mirrors defining a resonant cavity , in which is maintained a monolithic wave guide with a capillary
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH