S. Robin

Effect of Different Roughnesses on the Excitation by Photons of the Surface Plasmon of Aluminum

Different roughnesses induce changes of the interaction of incident light with surface-plasma oscillations. We observed those changes in the optical properties of aluminum. Identical aluminum films were deposited in ultrahigh vacuum (uhv) on substrates of varying roughnesses. We measured the reflectance at photon energies in the vicinity of the surface plasmon energy (1000–1600 A). We used overcoated substrates of different dielectrics (CaF2, MgF2, and LiF). In the terms of existing theories, we show that the curves are conveniently interpreted by taking into consideration (a) the light scattering by the surface characterized by the rms roughness σ and (b) the plasmon-photon interaction closely related to the roughness σand correlation length a. Thus, within the limit of accuracy (ΔR = ±0.5%) the roughness can be determined; σ is a function of the dielectric’s thickness with Δσ<0.5 A and the correlation length a (5 A<Δa<10 A) appears to be a characteristic of the nature of the dielectric. A study under an electron microscope confirms the theoretical strong value of roughnesses and shows the condensation process of aluminum on the rough substrates.

Influence of the substrate on the optical properties of evaporated films

Abstract Reflection measurements performed in ultrahigh vacuum on Al and Mg films show the existence of one reflection minimum in the frequency range of the surface plasmons. This minimum can be explained through the surface roughness, which gives diffusion and resonant coupling between the electric field of the incident wave and the surface plasmons. We have studied Al films 900 A thick in the wavelength range 1000–1600 A. Different kinds of roughness are induced by films of various dielectrics of different thicknesses previously deposited onto the Pyrex substrates. Theoretical curves have been deduced according to formulae of Davies and Ritchie correlating the two parameters describing the roughness of a substrate: σ, the mean height of the hills, and a , the autocorrelation length assuming a gaussian hill distribution. The preliminary results lead to the conclusion that the roughness depends on the nature and thickness of the dielectric substrate—the autocorrelation length a , peculiar to the individual substrate, determining the position of the reflection minimum.

Détermination des Constantes Optiques de Couches Minces Peu Absorbantes

On decrit une methode de determination des constantes optiques de couches minces peu absorbantes. Cette methode est appliquee au cas du fluorure de magnesium entre 1000 et 2000 +.

Asymmetric concave gratings: Theory and applications

A new concept is introduced in the theory of concave gratings: The center of the rectangular area used is not necessarily the vertex of the grating, but a point of the symmetry plane perpendicular to the grooves, lying at a varying distance w0 from it; the additional degree of freedom thus introduced permits an improvement of focus of some mountings commonly used at present.