Electromagnetic Resonances and Enhanced Nonlinear Optical Effects

Abstract

In this paper we present an electromagnetic (EM) theory of diffraction in nonlinear optics (NLO). We consider nonlinear (NL) media whose entrance face is not flat but constituted by a periodic rough surface (i.e. a grating with periodicity d and groove depth δ. Since it is impressed on a NL medium, we call such a grating a nonlinear grating). We consider NL optical processes of the kind (ω₁, ω₂) → ω₃ = ω₁ + ω₂. In the theory, we not only take into account the diffraction of the two pump beams ω₁ and ω₂ but also that of the signal at frequency ω₃. The theory applies to bare or multicoated gratings whatever the grating profile may be. Moreover, the groove depth δ is not considered as a perturbative parameter. Let us emphasize that the rigorous study of the surface plasmon resonance (SPR) contribution to enhanced NL optical effects such as surface-enhanced Raman scattering (SERS), second harmonic generation (SHG) constitute a special case of the theory of diffraction in NLO since these enhanced NL optical effects occur in NL media with rough entrance face.