Manufacturing Metrology Team

Coherence scanning interferometry for difficult manufacturing applications

Start: October 2016
Student: Carlos Gomez
Supervisors: Simon Lawes, Richard Leach, Rong Su
Industrial supervisor: Peter de Groot
Funding: CONACyT / The University of Nottingham

Coherence scanning interferometry (CSI) is a powerful, highly accurate non-contacting metrology method, which uses a broadband light source and combines vertical (z-axis) scanning with optical interferometry techniques, to achieve a three-dimensional surface measurement with sub-nanometre precision. Nevertheless, CSI has shown limited detectability when dealing with surfaces featuring high slopes, due to the limited numerical aperture of its objective optics.

Additive manufacturing (AM) is an example of a challenging application for CSI, wherein components produced by AM can have very rough surface texture with local slopes well beyond the NA limit. Other difficult cases for CSI involve Fresnel optics, because of scattering caused by discontinuities between the individual facets of these lenses. Diffuse, dissimilar, translucent, or porous surfaces also represent a challenge. These properties can significantly suppress the strength of any interferometric signals. However, most recent advances in CSI further expand the range of measurement parameters, offering significantly improved sensitivity to overcome these limitations.

This project consists of three main objectives:

  1. Development of guidelines to upgrade topographic measurement of CSI for difficult applications.
  2. Calibration of CSI through the determination and further development of the metrological characteristics, according to ISO standards.
  3. Improvement of the correlation between CSI and other surface metrology methods, e.g. contact stylus.
CSI measurement of the surface of a Ti6Al4V SLM sample, using a 20× objective lens (NA 0.40, stitched images of 0.42 mm × 0.42 mm field of view).
Zygo NewView 8300 CSI system at the MMT Laboratory.


Manufacturing Metrology Team

Room B38 Advanced Manufacturing Building
Jubilee Campus
Wollaton Road
Nottingham, NG8 1BB