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