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