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As described here, white light interferometry is a non-contact optical method for surface height measurement on 3-D structures with surface profiles varying between tens of nanometers and a few centimeters. It is often used as an alternative name for coherence scanning interferometry in the context of areal surface topography instrumentation that relies on spectrally-broadband, visible-wavelength light (white light). ==Basic principles== Interferometry makes use of the wave superposition principle to combine waves in a way that will cause the result of their combination to extract information from those instantaneous wave fronts. This works because when two waves combine, the resulting pattern is determined by the phase difference between the two waves—waves that are in phase will undergo constructive interference while waves that are out of phase will undergo destructive interference. While white light interferometry is not new, combining old interferometry techniques with modern electronics, computers, and software has produced extremely powerful measurement tools. Yuri Denisyuk and Emmett Leith, have done much in the area of white light holography and interferometry.〔Yu. N. Denisyuk, “Photographic reconstruction of the optical properties of an object in its own scattered radiation field,” Sov. Phys.-Dokl. 7, p. 543, 1962.〕〔Yu. N. Denisyuk, “On the reproduction of the optical properties of an object by the wave field of its scattered radiation,” Pt. I, Opt. Spectrosc. (USSR) 15, p. 279, 1963.〕〔Yu. N. Denisyuk, “On the reproduction of the optical properties of an object by the wave field of its scattered radiation,” Pt. II, Opt. Spectrosc. (USSR) 18, p. 152, 1965.〕〔Byung Jin Chang, Rod C. Alferness, Emmett N. Leith, “Space-invariant achromatic grating interferometers: theory (TE),” Appl. Opt., 14, p. 1592, 1975.〕〔Emmett N. Leith and Gary J. Swanson, “Achromatic interferometers for white light optical processing and holography,” Appl. Opt., 19, p. 638, 1980.〕〔Yih-Shyang Cheng, Emmett N. Leith, “Successive Fourier transformation with an achromatic interferometer,” Appl. Opt., 23, p. 4029, 1984.〕〔Emmett N. Leith, Robert R. Hershey, “Transfer functions and spatial filtering in grating interferometers,” Appl. Opt. 24, p. 237, 1985.〕 Currently, most interferometry is performed using a laser as the light source. The primary reason for this is that the long coherence length of laser light makes it easy to obtain interference fringes and interferometer path lengths no longer have to be matched as they do if a short coherence length white light source is used. For an interferometer to be a true white light achromatic interferometer two conditions need to be satisfied. First, the position of the zero order interference fringe must be independent of wavelength. Second, the spacing of the interference fringes must be independent of wavelength. That is, the position of all interference fringes, independent of order number, is independent of wavelength. Generally, in a white light interferometer only the first condition is satisfied and we do not have a truly achromatic interferometer. Even though there are a number of different interferometer techniques, three are most prevalent: # diffraction grating interferometers. # vertical scanning or coherence probe interferometers. # white light scatter-plate interferometers. While all three of these interferometers work with a white light source, only the first, the diffraction grating interferometer, is truly achromatic. All three are discussed by Wyant.〔Wyant, James in http://fp.optics.arizona.edu/jcwyant/pdf/Published_Papers/Optical_Testing/WhiteLightInterferometry.pdf〕 Here the vertical scanning or coherence probe interferometers are discussed in detail due to their extensive use for surface metrology in today’s high-precision industrial applications. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「White light interferometry」の詳細全文を読む スポンサード リンク
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