Suitable fixtures are developed and integrated with the computer system for generating three-dimensional surface and form data. Software for data acquisition, analysis of various parameters including new parameters and visualization of surface geometrical features has been developed. Both the intensity and the auto-focus methods are used to measure two-dimensional surface roughness by use of the system and results are presented.
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Filtering technology for three-dimensional surface topography analysis - ScienceDirect
When the distance from the beam splitter to the reference mirror is the same distance as the beam splitter is from the test surface and the split beams are recombined, constructive and destructive interference occurs in the combined beam wherever the length of the light beams vary. This creates the light and dark bands known as interference fringes. Since the reference mirror is of a known flatness — that is, it is as close to perfect flatness as possible — the optical path differences are due to height variances in the test surface. This interference beam is focused into a digital camera, which sees the constructive interference areas as lighter, and the destructive interference areas as darker.
In the interference image an "interferogram" below, each transition from light to dark represents one-half a wavelength of difference between the reference path and the test path. If the wavelength is known, it is possible to calculate height differences across a surface, in fractions of a wave.
From these height differences, a surface measurement — a 3D surface map, if you will — is obtained. Optical Profilers Obtain Amazing Accuracy with Interferometry Hypothetically, if the wavelength is nanometers, one could estimate the distance of slope over a full wavelength by looking at the light and dark interference bands — known as interference fringes — in an interferogram. Looking at the interferogram at right, you might notice that the light and dark bands near the bottom are not as bright or dark as the ones near the ruler marks.
This is because the lower portion of the interferogram is going out of focus; out of focus means less interference. By carefully calculating the area of greatest contrast, optical profilometers determine the point that has best focus. In practice, an optical profiler scans the material vertically. As the material in the field of view passes through the focal plane, it creates interference.
Each level of height in the test material reaches optimal focus and therefore greatest interference and contrast at a different time. With well-calibrated optical profilers, accuracy well below a nanometer is possible.
Modelling and simulation of surface topography in ultra-precision diamond turning
A nanometer is ten Angstroms. In a ZYGO profilometer , each data point is monitored to determine its most precise focal point. Every pixel's height is measured relative to every other by comparing its maximum contrast point of focus relative to the pixels around it — producing a very sensitive surface measurement.
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What is the Purpose of Optical Profiling? Non-contact profilometers are used in many situations where micro-measurement of surface variations are essential. Industries such as optics and data storage use highly polished surfaces that are measured with interference profilometers. Optics metrology is focused on lens and mirror surface finish and surface roughness , rate of curvature, and sometimes surface texture.
Optical Profiler Basics
Some binary lenses and diffraction gratings require measurements of volume, slope and radius of curvature. Click to get your Free copy of this handbook Data storage surface metrology concentrates not only on surface finish roughness, but also the surface shape of the disk at the edge, and the geometry of laser-textured bumps for minimizing 'stiction' the adhesive force of the read head to the magnetized surface. Bump spacing, their alignment to a grid, peak-to-valleys, consistency, and general bump shape are measured. These include flatness, angle, deviation from ideal form, roughness, and microstructure.
Surface Finish — ZYGO profilers measure surface roughness with better than nanometer and microinch specification - well below the level of detection by the human eye or tactile sensation. Step Height — ZYGO surface profilers can measure height difference between two discontinuous planes of up to 20 mm. It is also possible to measure the angle of the surfaces using this technique.
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Dynamic Metrology — MEMS research and production requires precise surface measurement and characterization of micro-devices. Films — The top surface and film thickness data analysis capabilities enable precise measurement of various surfaces in multilayer processes. Special algorithms single out the film's top surface to measure its topography, while film thickness analyses identify the film's top surface and the substrate surface to calculate a film thickness map.
These special analyses also permit topography measurement of the substrate surface.