Zygo surface metrology

We recently held a successful Zygo seminar on high performance optical surface profiling at the NPL, giving over 50 industry and academic participants an opportunity to gain a better understanding of how Zygo metrology tools can help characterise surfaces and improve R&D and manufacturing processes. Zygo provide two basic tools, one based on scanning white light interferometry and the other on Fizeau interferometry and we often get asked which one should be used for a particular application or what's the difference between the two? So here I will provide a brief explanation.

The Zygo NewView scanning white light interferometer is a general purpose surface metrology tools designed to cope with most surface topographies and textures. Depending on the quality of light reflection from the surface it will allow measurement of surfaces from a very small field of view (0.22 mm square) but with high magnification (100x) to a large field of view (22 mm square) with very low magnification (0.5x). This makes the NewView very versatile for measuring surfaces ranging from super smooth all the way to poorly reflecting surfaces with roughness values of tens of microns. Typical applications range from highly polished diamond machined surfaces such as contact lens moulds to embossed paper and rough coatings from screen printed materials. When measuring rough surfaces best results are achieved with a high magnification setting on the tool which means that "stitching" of several fields of view is required to observe a large area of several to tens of mm square.

The Zygo GPI is a Fizeau interferometer using a laser light source, it relies on a comparison of the surface under test with a reference optical surface, allowing measurement of flat or spherical components. The field of view is typically large from 4" diameter and more but the surface needs to be reflective and typically shiny to the naked eye to ensure enough laser light reflected off the surface can make its way back into the instrument. The GPI uses a similar camera to the NewView and with the larger aperture this means it will have a lower optical resolution than can be achieved with the NewView. Surfaces are measured on the GPI to determine form rather than roughness and typically this includes optical components and shiny diamond machined parts such as contact lenses and orthopaedic hip joints where the departure of the surface from either flat or sphere is no more than a few microns.

For more information take a look at: http://www.lambdaphoto.co.uk/products/140.003