The stability of the Shack-Hartmann sensor against mechanical disturbances from the environment can advantageously be exploited in highly sensitive wave front tests of surfaces. Here, a Fizeau-type multiple beam test is investigated. The enhancement of the phase sensitivity in a Fizeau-resonator formed by two high reflecting mirror surfaces enables tests in reflected light which includes also opaque surfaces. The multiplication of the sensitivity with the number of passes through the Fizeau resonator provides a big margin against the rather limited repeatability of wave front measurements with such a wave front sensor. The method has been tested for planeness Fizeau measurements. It could also be exploited in spherical Fizeau tests. But in the latter case the two spherical surfaces forming the resonator should have radii which differ only by e.g. 1mm.
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