• DOI:10.1209/0295-5075/96/64004
• Corpus ID: 118853828

Spectrum of Radiation from Rough Surfaces

@inproceedings{ZhSGevorkian2011SpectrumOR,
  title={Spectrum of Radiation from Rough Surfaces},
  author={Zh.S.Gevorkian},
  year={2011}
}

• Zh.S.Gevorkian
• Published 3 August 2011
• Physics

Radiation from a charged particle travelling parallel to a rough surface has been considered. Spectral-angular intensity is calculated in the weak scattering regime. It is shown that the main contribution to the radiation intensity is determined by the multiple scattering of polaritons induced by a charge on the surface. Multiple scattering effects lead to strong frequency dependence of radiation intensity. Possible applications in beam and surface diagnostics are discussed. Introduction. – Light scattering from rough surfaces attracted much interest [1]. In particular this interest is caused by the determination of microtopographic properties of rough metallic surfaces from the light scattering measurements [2]. The enhancement of intensity of scattered light on a rough surface is due to a resonant excitation of surface polaritons induced by incident light. Surface polaritons are multiply scattered on the roughness resulting in their diffusion and localisation [3] that lead to peculiarities in the light scattering from rough surfaces. Polaritons can be induced not only by an incident light but also by a charged particle. It is interesting to reveal the manifestation of polaritons multiple scattering on the charged particle radiation from rough surfaces. Origination of this radiation is due to the scattering of polaritons induced by the charged particle on the inhomogeneites of dielectric constant associated with the roughness of the surface. Earlier in this geometry main attention was paid to the periodical grating case when Smith-Purcell radiation(SPR) [4] is originated. Recently we have considered [5] the radiation from an uncorrelated rough surface. In the present paper we consider the influence of multiple scattering effects, including the localisation of polaritons, on the radiation of a charged particle travelling over a correlated rough surface.We will see that they lead to strong frequency dependence of intensity. Strong frequency dependence allows to separate the diffusional mechanism of radiation from other radiation mechanisms. Formulation of the Problem. – A charged particle moves uniformly in the vacuum at the distance d from the plane z = 0 separating vacuum and the isotropic medium distorted by roughness. We are interested in radiation field far away from the charge and interface. Maxwell equation for the electric field has the form ∇ ~ E(~r, ω)− graddivẼ(r̃, ω) + ω 2 c2 ε(r̃, ω)Ẽ(r̃, ω) = j̃(r̃, ω) (1) where ~j(~r, ω) = − 4πieω~v vc2 δ(z − d)δ(y)e is the current density associated with the charge. Here ~v is the velocity of the particle moving on 0x direction and ε(~r, ω) is the inhomogeneous dielectric permittivity of the system. For a rough surface it can be chosen as ε(~r, ω) = ε0(z, ω) + εr(~r, ω), where ε0(z, ω) = Θ(z) + Θ(−z)ε(ω) descibes the flat interface vacuum-metal and εr(~r, ω) = [ε(ω)−1]δ(z)h(x, y) is the contribution of small roughness. h(x, y) is the amplitude of surface roughness. To separate the radiation field one should decompose the electric field as ~ E = ~ E0+ ~ Er, analogous to the decomposition of dielectric constant. ~ E0 and ~ Er are the background field created by the charge and the radiation field,respectively. They obey the following equations ∇ ~ E0(~r, ω)− graddivẼ0(r̃, ω) + + ω c2 ε0(z, ω) ~ E0(~r, ω) = ~j(~r, ω) (2) ∇ ~ Er(~r, ω)− graddivẼr(r̃, ω) + ω c2 ε(z, ω)Ẽr(r̃, ω) + + ω c2 εr(~r, ω) ~ Er(~r, ω) = − ω c2 εr(~r, ω) ~ E0(~r, ω) (3) Radiation intensity at the frequencies ω, ω + dω and at the angles Ω, Ω + dΩ is determined as dI(ω, ~n) =