The optical techniques are non-contact, non-destructive and highly efficient for diagnostics of rough surfaces. The optical techniques may be divided into profile interference and heterodyning techniques, techniques based on measuring of the angular distribution of scattered radiation, and optical correlation techniques. High operation rates, data processing in the optical channel, high accuracy of measurements, feasibilities for real-time data processing, and small sizes of the measuring devices are the main advantages provided by optical correlation diagnostic methodology. However, when the height of surface inhomogeneities exceeds the wavelength of the probing beam, and the specular component of the reflected radiation is absent, the unambiguous connection between the statistical parameters of the roughness and of the scattered field is lost. The new approaches of fractal and singular optics are consequently needed for diagnostics of such surfaces. At the same time, these approaches so far provided only classification of rough surfaces into random and fractal ones.
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