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