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