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Figure 1: Schematic layout of a White-light Interferometer. A CCD image sensor like those used for digital photography is placed at the point where the two images are superimposed. A broadband “white light” source is used to illuminate the test and reference surfaces. A condenser lens collimates the light from the broadband light source.
Figure 3. White light interferometric microscope. White-light interferometry scanning (WLS) systems capture intensity data at a series of positions along the vertical axis, determining where the surface is located by using the shape of the white-light interferogram, the localized phase of the interferogram, or a combination of both shape and phase.
White light interferometry is commonly used for detecting deformations of the wafer surface based on optical measurements. Low-coherence light from a white light source passes through the optical top wafer, e.g. glass wafer, to the bond interface. Usually there are three different white light interferometers: diffraction grating interferometers
Diffraction-grating interferometer (white light) Double-slit interferometer; Dual-polarization interferometry; Fabry–Pérot interferometer; Fizeau interferometer; Fourier-transform interferometer; Fresnel interferometer (e.g. Fresnel biprism, Fresnel mirror or Lloyd's mirror) Fringes of Equal Chromatic Order interferometer (FECO) Gabor hologram
they can measure surfaces through transparent medium such as glass or plastic film; non-contact measurement may sometimes be the only solution when the component to measure is very soft (e.g. pollution deposit) or very hard (e.g. abrasive paper). Vertical scanning: Coherence scanning interferometry; Confocal microscopy; Focus variation
DHM performs static measurements of 3D surface topography as many other 3D optical profilometers (white light interferometers, confocal, focus variation, ... ). It enables to retrieve, roughness and shape of many surfaces. [32] [33] [34] Use of multiple wavelengths enable to overcome the l/4 limit of traditional phase shifting interferometers ...