Patent ID: 11892283
Assignee: CARL ZEISS SMT GMBH
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 8:
9. A method for calibrating a diffractive optical element, which is configured to produce a test wave with a wavefront formed as a free-form surface for interferometrically determining a shape of a surface of a test object, comprising:
providing the diffractive optical element with multiple encoding and radiating in an input wave, to produce a calibration wave directed at a calibration object in addition to the test wave, by diffraction at the multiple encoding,, wherein the calibration wave has a wavefront with a non-rotationally symmetric shape,
arranging the calibration object at different calibration positions such that the calibration wave is respectively substantially perpendicularly incident on different regions of a surface of the calibration object, and
capturing and comparing calibration interferograms which are produced by superimposing a reference wave with the calibration wave after interacting with the calibration object at the different calibration positions.