{HEAD ~ Each} of the layers 112 is separated by {TAIL ~ a second relatively thick layer} 116 composed of a material having a relatively low index of refraction 
is separated by
{ HEAD ~ Each } of the layers 112 is separated by { TAIL ~ a second relatively thick layer } 116 composed of a material having a relatively low index of refraction
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH