Extraction of light into {TAIL ~ a particular direction} with in plane wavevector k is related to {HEAD ~ the source emission Sk′} into all those modes with in plane wavevector k′ that are compatible to k by the addition or subtraction of a reciprocal lattice vector G, i.e k=k′±G 
Extraction of light into { TAIL ~ a particular direction } with in plane wavevector k is related to { HEAD ~ the source emission Sk′ } into all those modes with in plane wavevector k′ that are compatible to k by the addition or subtraction of a reciprocal lattice vector G , i.e k = k′±G
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD 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 OTH OTH OTH OTH OTH OTH OTH