{HEAD ~ An optical element} 13, wherein {TAIL ~ the first reflectivity} is the substantially maximum reflectivity for the material 
wherein
{ HEAD ~ An optical element } 13 , wherein { TAIL ~ the first reflectivity } is the substantially maximum reflectivity for the material
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH