{TAIL ~ A pair} of {HEAD ~ photodetector output signals} are positioned so as to be responsive to the interference pattern produced by the pair of laser beams of the ring laser 
{ TAIL ~ A pair } of { HEAD ~ photodetector output signals } are positioned so as to be responsive to the interference pattern produced by the pair of laser beams of the ring laser
TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH