An optical surface roughness and waviness sensor for sufficiently smooth surfaces is introduced. The sensor is based on a computer-generated hologram , which focuses the specular reflectance to desired spots on the focal plane. Computer simulations were made to analyze the system and to compute the calibration curve. Contrast analysis was performed to estimate the average roughness of Gaussian surfaces. Results are compared with data measured form surface roughness standards.
The conventional computer generated holograms (CGH) presented in literature are calculated with the discrete Fourier transform (FFT). In optical reconstruction of the CGH the spatial components diffracted from a photographically reduced hologram are collected by a lens to produce a reconstructed picture. The angles between the diffracted spatial components and the optical axis are typically in the range of milliradians. On the other hand, computer generated diffraction gratings can be calculated without any Fourier transformation by using discrete wavefront theories. The reduction of the holograms to the right scale can be made, e.g., by using focused electron beam, focused laser beam, or photographic process. In our applications some diffraction gratings are calculated with the aid of the Stardent 3040 system with four MIPS R3000 parallel processors (64 MB) and reduced by using photographic processes to complete the diffraction gratings into optical range applied by the conventional holography.
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