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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.
The fact that these sensors have no moving parts allows for very high scan speeds and makes them very repeatable. Configurations with a high numerical aperture can measure on relatively steep flanks. Multiple sensors, with the same or different measurement ranges, can be used simultaneously, allowing differential measurement approaches (TTV) or ...
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
Figure 1. The light path through a Michelson interferometer.The two light rays with a common source combine at the half-silvered mirror to reach the detector. They may either interfere constructively (strengthening in intensity) if their light waves arrive in phase, or interfere destructively (weakening in intensity) if they arrive out of phase, depending on the exact distances between the ...
White light interferometry is utilized to detect deformations of the wafer. Low coherence light from a white light source passes through the top wafer to the sensor. The white light is generated by a halogen lamp and modulated. The spectrum of the reflected light of the sensor cavity is detected by a spectrometer. The captured spectrum is used ...
There are many different techniques which are currently being employed, such as laser triangulation (triangulation sensor), confocal microscopy (used for profiling very small objects), coherence scanning interferometry, and digital holography. Advantages of optical profilometers are speed, reliability and spot size.
Michelson interferometers using a white light source White light has a tiny coherence length and is difficult to use in a Michelson (or Mach–Zehnder ) interferometer. Even a narrowband (or "quasi-monochromatic") spectral source requires careful attention to issues of chromatic dispersion when used to illuminate an interferometer.