Proceedings PaperStrong Scattering By Surfaces Of Small Roughness
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A surface diffuser is said to be strong, if scattered radiation does not contain a specular component. Making use of the expression which relates the magnitude of this component to the density function of surface roughness the condition of strong scattering is formulated in terms of surface statistics. It is shown that rms roughness, being the functional of the roughness density, can be minimized under the condition that specular component does not appear, however a standard method of calculus of variations can not be applied. In the present study two sequences of the continuous density functions are proposed. Each density fulfills the strong scattering condition and variances of subsequent densities decrease. In both cases the limit density is discrete and characterizes a binary diffuser which introduces two phase shifts ¶/2 and -¶/2 (each one with the probability equal to 0.5). Rms phase of such a diffuser equals ¶/2 rad. Reasoning is presented which justifies that any other density function either yields rms phase greater than ¶/2 or causes the specular component to appear. It is shown that there are two types of the continuous density functions which closely approximate the limit function. Both types are bimodal and symmetric. An example of the continuous density of phase is given which is positive in the (-φo,φo) interval, where φ =2.4 rad and whose rms phase equals 1.7 rad (i.e. it is greater than limit value ¶/2 by 8ξ)). The present study shows that strong scattering can be performed by quite smooth surfaces and consequently a speckle pattern of high contrast can be observed in this case.