Advantages of on-axis PBS based Fizeau interferometers

The common path arrangement of Fizeau interferometers is the reason why they are most commonly used for the measurement of optical flats, spheres and aspheres. However, the interference signal of the surface under test (SUT) and the reference is not sinusoidal. This results in an increased uncertainty of the measurement. The potential of phase shifting algorithms cannot be used. How to make use of the advantages and how to avoid the drawbacks? A patent-pending embodiment uses on-axis polarization beam splitters (PBS). The interference is sinusoidal. The potential of phase shifting algorithms can be used. In addition, it will be described how advanced analysis can significantly reduce the uncertainty even further. Interference contrast V >0.9 can be obtained for a wide range of the degree of reflection of the SUT. Furthermore, there are no moving parts. This enables measurements in vibration-exposed environments. A five phase shifting algorithm might be carried out within less than 1/200 s. The described embodiment and the related analysis enables a significant reduction of the uncertainty of the phase measurement. It opens up new applications in the field of dynamic interferometry.