Patent ID: 7791737

Claim:
A method for interferometrically determining a deviation of an actual shape of an effective reflection surface of a test object from a desired shape of the effective reflection surface, comprising: producing electromagnetic illumination radiation with an illumination device and providing the radiation as an input wave, passing the input wave through a diffractive optical element, to exit the element as an incoming measuring wave, the wave front of which is adapted to a desired shape of the effective reflection surface, disposing the test object in a test position in which the incoming measuring wave is reflected back to the diffractive optical element by the effective reflection surface of the test object as a reflected measuring wave, passing the reflected measuring wave through the diffractive optical element, to exit the diffractive optical element as an outgoing measuring wave, the propagation direction of the outgoing measuring wave being deviated upon exiting the diffractive optical element in relation to the opposite propagation direction of the input wave upon passing into the diffractive optical element, branching off a reference wave from the illumination radiation such that the reference wave interferes with the outgoing measuring wave, and recording an intensity distribution of an interference pattern produced by the interference of the reference wave with the outgoing measuring wave with a recording device.