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Tilted Wave Interferometry has been invented and developed over the last years as a flexible and very fast method to test precision aspheres and freeform surfaces . It measures surface deviations full field, with high lateral resolution, without any null compensator like CGH and without moving the tested part while measuring. The test of non-spherical optical components is a topic of high relevance for optics industry, as current optic designs rely heavily on those elements, since the small form factors and high performance of actual designs would be impossible with traditional spherical optics designs. As all precision components, aspheres and freeform surfaces need accurate testing for their production. Ideally, testing of components is closely integrated into the fabrication chain. Due to the high flexibility and measurement speed of the TWI of typically less than 30 sec it is well suited for this purpose. Due to the special illumination scheme, the first implementations of this new interferometer have been of Mach Zehnder type. In this contribution we demonstrate, how the tilted wave interferometer principle can be implemented in a Fizeau configuration. The benefit of this configuration against the Mach Zehnder configuration is the common path feature. Here, the reference beam and the measurement beam follow the same optical track inside the interferometer, making the interferometer much more robust against temporal environmental influences such as vibrations and air turbulences. At the same time, form tolerances of the interferometer components in the common path area can be relaxed. These advantages of Fizeau are well known. The multiple source illumination of the tilted wave interferometer however leads to the generation of multiple reference wavefronts that can be disturbing. We therefore present a new TWI implementation that avoids these problems. It relies on a new illumination design with four sets of illumination patterns that each generate their own reference wave. The new approach has been implemented in a lab setup and shows in first measurements the expected improvements in stability. We tested the system in extensive Monte Carlo simulations. The common path approach showed a reconstruction error of the test specimen of up to an order of magnitude lower compared the Mach-Zehnder configuration.
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