In this representation, r is the position at which ˜E is evaluated, ˆe is the reference polarization expressed as a unit vector, and k is the unit v...In this representation, r is the position at which ˜E is evaluated, ˆe is the reference polarization expressed as a unit vector, and k is the unit vector ˆk in the direction of propagation, times β; i.e.: ˆe=(ˆe⋅ˆx)ˆx+(ˆe⋅ˆy)ˆy+(ˆe⋅ˆz)ˆz