Suppression of radiation in a momentum nonconserving nonlinear interaction

Summary form only given. Since the pioneering work by Drexhage (1974) where he considered the radiation of dye molecules in front of a mirror surface, it has been shown in many occasions that the pattern of radiation in free space can be modified. More recently, it was suggested that these changes could be equally seen from the radiation of dipoles in photonic crystals and in very simple systems where the radiation is emitted only in one or two directions. In an experiment of second harmonic (SH) generation in front of a mirror, corresponding to the radiation of a sheet of dipoles at a distance from a surface boundary, Kauranen et al. (1998) observed that even when the total rate of radiation was suppressed, the field between the dipole sheet and the boundary was finite and independent of this total rate. We have shown that this apparent contradiction can only be explained if the quadratic nonlinear interaction includes terms not conserving momentum such as the term that considers the transfer of energy from the reflected SH field to the incident fundamental and vice versa. In bulk generation of SH light the contribution of such terms would vanish, however, in surface generation or from a subwavelength layer, momentum is conserved due to the presence of a nearby interface between a linear and a nonlinear material. We have considered a simple one-dimensional model where SH light is generated from a fundamental beam incident onto a thin nonlinear layer separated by a variable distance from a mirror.