White Light Interferometer WLI - Fries Research & Technology

White light interferometry is a fast method to perform 3D topographical measurements. It utilizes a light source with very low temporal coherence. By means of a beam splitter this light is separated into a reference beam (reflected to a reference mirror) and an object beam that strikes the surface to be measured.The light reflected from both, the reference mirror and the measured object, is overlayed. This interference pattern is captured by a camera.

Whilst performing the topography measurement, the objective is gradually moved in small steps into z-direction. At each position the camera takes a single image. Then, all images are compiled into an image stack, which is used to render the 3D topography.

Due to the low temporal coherence of the white-light the WLI FL characterizes reflective and rough surfaces as well as step heights with very good height resolution, which is typical for interferometric measurement approaches.

non-contact topography measurement
sub-nanometer height resolution
very fast 3D measurements
measurement of highly reflective, rough or structured surfaces

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roughness measurement in nm-range, e.g. on optical
components such as mirrors or lenses
evaluation of micro structures (e.g. MEMS, microfluidics, microoptics)
measurement of step-height in the field of semiconductors
measurement on different materials (e.g. metal, semiconductors, glass,
plastics, paper, lacquers, and coatings)
measurement on liquids

Lens (Mirau)	10	20	50 ⁽¹⁾
Measuring Range z ⁽²⁾	100 µm	100 µm	100 µm
Measuring Range x, y (mm)	1.6 x 1.2	0.8 x 0,6	0.32 x 0.24
Working Distance (mm)	3.6	3.6	1.7
Sampling Intervall (x, y in mm)	2.5	1.25	0.5
Resolution z (nm)	0.1	0.1	0.1
Working Temperature ⁽³⁾	20°C ± 2°C	20°C ± 2°C	20°C ± 2°C
¹ 50x lens optional ² optional up to 400 µm ³ operating temperature: 5°C - 40°C