Resonance effects in a dielectric grating; total absorption of electromagnetic waves by a dielectric grating on metal system

The coupled wave method (CWM) is used to analyse electromagnetic wave diffraction by a dielectric grating mounted on dielectric or metallic substrates. Under certain conditions there occurs coupled wave resonance (CWR) that consists in an abrupt increase of the electromagnetic field inside the grating. The CWR characteristics depend on the magnitude of the grating dielectric constant modulation, and in the case of a dielectric substrate the reflection index tends to unity, while for a metallic substrate it tends to zero (resonance absorption in metal). Using the CWM the grating parameters were found for platinum and potassium for a wavelength of 0.85 µm and for gold for a wavelength of 1.5 µm provided that the reflection index of such a system is less than 0.0001. For Pt and K, relations of the reflection index to the grating thickness and wavelength of TE and TM polarizations were obtained. There is an especially abrupt dip in the reflection index for potassium. This is due to the fact that the reflection index for pure K is greater than 0.97. The reflection dependence on the wavelength for resonance absorption may be described quite accurately using the Lorentz distribution.