Study of the possibility to measure the root-mean-square roughness of a shaded rough surface

The estimate of the root-mean-square roughness of a rough surface σ₁ is studied experimentally as a function of the angle of incidence. A surface with σ=1.3 μm is illuminated by laser radiation with a wavelength of 0.633 μm. The angle of incidence of radiation on the surface under study is varied from 85° to 87.5°. σ₁ is estimated under the assumption that the regime of a slightly rough surface is fulfilled for the surface studied. Theoretical estimates of σ₁ are calculated in the Kirchhoff approximation with rough surface shadowing taken into account. The greatest relative difference between experimental and theoretical estimates of σ ₁ does not exceed 0.07. The effect of rough surface shadowing on the estimate of σ is analyzed, and the possibility for exact measurement of σ₁ of a shaded rough surface is demonstrated in the case of a priori knowledge of the angle of incidence, for which this measurement is possible. A method that makes it possible to determine the angle of incidence, for which a good agreement between the measured value and the true value of σ of a shaded rough surface is possible, is proposed.