Chromatic confocal spectral interferometry (CCSI)

Chromatic Confocal Spectral Interferometry (CCSI) is a hybrid measurement principle for 3D topometry without the need for axial scanning. CCSI benefits from the precision of interferometric principles as well as the robustness of confocal microscopy, while avoiding most of their individual shortcomings. Based on axial separation of foci and spectral detection of a white-light signal, it provides single-shot measurements.

For Spectral Interferometry (SI), measurement range is limited by the depth of focus of the microscope objective. As depth of focus, as well as lateral resolution, are depending on the numerical aperture of the system, there is always a tradeoff between large measurement range and high lateral resolution. By chromatic separation and confocal filtering, CCSI overcomes this link. This enables a sensor, which combines high lateral resolution and large axial measurement range.

In addition to the CCSI sensor mentioned before, which are single-shot point sensors, the concept of combining SI and chromatic encoding was transferred to a line sensor design. Each point of the line gets illuminated by a specific wavelength. Therefore the spectral signal encodes the object height of each illuminated point as well as its position.

Signal evaluation for CCSI

One of the main advantages of CCSI is that the axial position of the object is encoded in both, confocal envelope and interferometric wavelet. In contrast to scanning white light interferometry, both information channels are intrinsicly decoupled, yielding robust evaluation strategies. The confocal enveloped can be assessed by a simple center-of-gravity calculation. But the resolution is limited to that of confocal microscopy and also the known artifacts are present in the result. However, the interferometric information provides much higher resolution, but fails on discontinuities or steep gradients. Fig. 1 shows a comparison of both evaluation methods (Fig. 1a), as well as the results of a combined algorithm, that uses both evaluation paths and therefore provides a more robust evaluation (Fig. 1b).

Publications

  1. Gronle, Marc; Lyda, Wolfram; Mauch, Florian; Osten, Wolfgang: Laterally chromatically dispersed, spectrally encoded interferometer. In: Applied Optics 50 (2011), Nr. 23, S. 4574
  2. Gronle, Marc; Lyda, Wolfram; Mauch, Florian; Osten, Wolfgang: Spectral Interferometry with Lateral Chromatic Encoding. In: 10th IMEKO Symposium : Laser Metrology for Precision Measurement and Inspection in Industry (LMPMI) 2011, VDI Verlag, 2011, S. 97–104
  3. Lyda, Wolfram; Fleischle, David; Haist, Tobias; Osten, Wolfgang: Chromatic confocal spectral interferometry for technical surface characterization. In: Proceedings of SPIE 7432 (2009), S. 74320Z–74320Z–9
  4. Lyda, Wolfram; Fleischle, David; Mauch, Florian; Haist, Tobias; Osten, Wolfgang: Vor- und Nachteile der chromatisch-konfokalen Spektralinterferometrie im Vergleich zur klassischen Spektralinterferometrie. In: 111. Jahrestagung, 2010 (DGaO-Proceedings), S. B31
  5. Lyda, Wolfram; Gronle, Marc; Fleischle, David; Mauch, Florian; Osten, Wolfgang: Advantages of chromatic-confocal spectral interferometry in comparison to chromatic confocal microscopy. In: Measurement Science and Technology 23 (2012), Nr. 5, S. 054009
  6. Lyda, Wolfram; Körner, Klaus; Osten, Wolfgang: Einsatz der chromatischkonfokalen spektralen Interferometrie (CCSI) zur Reduktion der Messunsicherheit bei chromatischkonfokalenTopografiemessungen. In: 109. Jahrestagung, 2008 (DGaO-Proceedings), S. P15
  7. Papastathopoulos, Evangelos; Körner, Klaus; Osten, Wolfgang: Chromatic confocal spectral interferometry - (CCSI). In: Osten, Wolfgang (Hrsg.): Fringe 2005, 2005, S. 694–701
  8. Papastathopoulos, Evangelos; Körner, Klaus; Osten, Wolfgang: Chromatic confocal spectral interferometry. In: Applied Optics Letters 45 (2006), Nr. 32, S. 8244–8252
  9. Papastathopoulos, Evangelos; Körner, Klaus; Osten, Wolfgang: Chromatically dispersed interferometry with wavelet analysis. In: Optics Letters 31 (2006), Nr. 5, S. 589–591
  10. Papastathopoulos, Evangelos; Lyda, Wolfram; Körner, Klaus; Osten, Wolfgang: Chromatisch-konfokale Spektral- Interferometrie (CCSI). In: VDI (Hrsg.): VDI-Berichte 1996 Bd. 1996. 2007, S. 309–318
  11. Boettcher, Tobias; Lyda, Wolfram; Gronle, Marc; Mauch, Florian; Osten,Wolfgang: Robust signal evaluation for chromatic confocal spectral interferometry. In: SPIE Optical Metrology 2013, Proceedings of SPIE, S. 87880W, SPIE, 2013.
  12. Boettcher, Tobias; Gronle, Marc; Mauch, Florian; Osten,Wolfgang: A more robust and flexible approach to laterally chromatically dispersed, spectrally encoded interferometry (LCSI). In: SPIE Photonics Europe 2014, Proceedings of SPIE, S. 913211-1, SPIE, 2014
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