Physikalisch-Technische Bundesanstalt

Assessing the optical quality of surfaces by means of a Fizeau interferometer is considerably more complex if the surfaces under test show different reflectivities. Up to now, several reference surfaces have been necessary. PTB has developed a Fizeau interferometer which makes this redundant. Now, maximum contrast can be attained regardless of the reflectivity of the sample. This is achieved by introducing a commercially available, so-called “on-axis beam splitter” which splits the light irradiated along the axis of symmetry. Sample characterization is simplified by the reduction to a two-beam interference. Finally, the increased measurement dynamics enable topography measurements also in environments affected by vibrations.