DUV-Shearing Interferometer with reduced spatial and temporal coherence

A shearing interferometer based on two ronchi gratings will be presented. The whole setup is working with an excimer laser at lambda=193nm. This light source always comes with a reduced temporal and spatial degree of coherence. As the shearing interferometer is a common path setup the partially temporal coherence does not affect the interferometric measurement, but can be used instead to destroy the spatial coherence. So, disturbing interferences are reduced. To increase the contrast of the desired interferometric fringes the spatial coherence of the illuminating wave front is adapted to the shearing distance. The system is used to measure small local changes of the optical path of a few nm which are induced for example by small changes of the thickness or the refractive index of a quartz cube.