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A White Light Scanner (WLS) is a device for performing surface height measurements of an object using Coherence Scanning Interferometry (CSI) with spectrally-broadband, "white light" illumination. Different configurations of scanning interferometer may be used to measure macroscopic objects with surface profiles measuring in the centimeter range, to microscopic objects with surface profiles measuring in the micrometer range. For large-scale non-interferometric measurement systems, see structured-light 3D scanner. ==Description== Vertical Scanning Interferometry is an example of low-coherence interferometry, which exploits the low coherence of white light. Interference will only be achieved when the path length delays of the interferometer are matched within the coherence time of the light source. VSI monitors the fringe contrast rather than the shape of the fringes. Fig. 2 illustrates a Twyman–Green interferometer set up for white light scanning of a macroscopic object. Light from the test specimen is mixed with light reflected from the reference mirror to form an interference pattern. Fringes appear in the CCD image only where the optical path lengths differ by less than half the coherence length of the light source, which is generally on the order of micrometers. The interference signal (correlogram) is recorded and analyzed as either the specimen or reference mirror is scanned. The focus position of any particular point on the surface of the specimen corresponds to the point of maximum fringe contrast (i.e. where the modulation of the correlogram is greatest). Fig. 3 illustrates a white light interferometric microscope using a Mirau interferometer in the objective; other forms of interferometer used with white light include the Michelson interferometer (for low magnification objectives, where the reference mirror in a Mirau objective would interrupt too much of the aperture) and the Linnik interferometer (for high magnification objectives with limited working distance). The objective (or alternatively, the sample) is moved vertically over the full height range of the sample, and the position of maximum fringe contrast is found for each pixel.〔(【引用サイトリンク】url=http://www.azom.com/article.aspx?ArticleID=4778 )〕 The chief benefit of low-coherence interferometry is that systems can be designed that do not suffer from the 2 pi ambiguity of coherent interferometry, and as seen in Fig. 1, which scans a 180 µm × 140 µm × 10 µm volume, it is well suited to profiling steps and rough surfaces. The axial resolution of the system is determined by the coherence length of the light source and is typically in the micrometer range.〔Wojtek J. Walecki, Kevin Lai, Vitalij Souchkov, Phuc Van, SH Lau, Ann Koo physica status solidi (c) Volume 2, Issue 3 , Pages984 - 989〕〔W. J. Walecki et al. "Non-contact fast wafer metrology for ultra-thin patterned wafers mounted on grinding and dicing tapes" Electronics Manufacturing Technology Symposium, 2004. IEEE/CPMT/SEMI 29th International Volume , Issue , July 14–16, 2004 Page(s): 323 - 325〕〔more references on semiconductor applications of low coherence interferometry are provided on http://www.zebraoptical.com/services.html〕 Industrial applications include in-process surface metrology, roughness measurement, 3D surface metrology in hard-to-reach spaces and in hostile environments, profilometry of surfaces with high aspect ratio features (grooves, channels, holes), and film thickness measurement (semi-conductor and optical industries, etc.).〔Examples of fiber-based low coherence interferometry applications are provided on http://www.novacam.com/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 scanner」の詳細全文を読む スポンサード リンク
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