Boundary conditions on exciton polarization and mode coupling in a spatially dispersive medium

A mode coupling condition recently derived in an investigation of the structure of the electromagnetic field in a spatially dispersive model medium is shown to imply that each mode of the exciton polarization obeys a certain inhomogeneous boundary condition. The total exciton polarization is shown to obey a boundary condition that has the form of an extinction theorem. The results are exact consequences of the Maxwell equations and of the constitutive relation alone. A brief comparison of our new boundary condition with the additional boundary conditions previously proposed by Pekar, by Hopfield and Thomas and by Sein is also made