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