Prior art devices wherein the thickness of the layers was not calculated to optimize light efficiency had {HEAD ~ a product} of {TAIL ~ phase factors} ξ1 and ξ2 of less than 80% 
of
Prior art devices wherein the thickness of the layers was not calculated to optimize light efficiency had { HEAD ~ a product } of { TAIL ~ phase factors } ξ1 and ξ2 of less than 80 %
OTH 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 OTH OTH OTH OTH OTH OTH OTH OTH