Measurement device for interferometric measurement of a surface shape

A method for interferometrically measuring a shape of a surface of a test object in relation to a reference shape, comprising:

• radiating at least a portion of a test wave, generated with a diffractive optical element, onto the surface of the test object, the wavefront of the test wave being adapted to a target shape of the surface of the test object and the target shape being configured as a first non-spherical surface,
• providing a reference element with a reference surface having the reference shape, the reference shape being configured as a further non-spherical surface and the reference element comprising a low thermal expansion material with a mean coefficient of thermal expansion having an absolute value of no more than 200×10−6 K−1 in a temperature range from 5 °C to 35 °C, and
• generating an interference pattern by superimposing the test wave after an interaction with the surface of the test object with a reference wave, whose radiation was exposed to an interaction with the reference surface,
• wherein the diffractive optical element comprises a diffraction pattern, a fill factor of which has a variation over a cross section of the emitted test wave, the variation being adapted to a variation in the thickness of the reference element over a cross section of the radiated-in test wave.