Measuring device for interferometrically measuring a surface form

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

• a diffractive optical element configured to generate a test wave from measurement radiation, a 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,
• a reference element with a reference surface which has the reference shape, the reference shape being configured as a further non-spherical surface,
• a first holder configured to arrange the test object in a beam path of the test wave in a measurement configuration, and
• a further holder configured to arrange the reference element in a beam path of a reference wave in the measurement configuration,
• wherein the reference element has a hole and the diffractive optical element is configured to generate the test wave with a convergent beam path such that a caustic of the test wave is generated in the hole of the reference element arranged in the beam path of the reference wave.

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

• radiating at least a portion of a test wave, generated by a diffractive optical element, onto the surface of the test object which is arranged in a beam path of the test wave with a first holder, 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,
• arranging a reference element in a beam path of a reference wave with a further holder, the reference element comprising the reference surface having the reference shape and the reference shape being configured as a further non-spherical surface, and
• superimposing the test wave, following an interaction of the test wave with the surface of the test object, with the reference wave, whose radiation was exposed to an interaction with the reference surface,
• wherein the reference shape deviates from the target shape of the surface of the test object by no more than 500 μm.