Method of measuring a deviation of an optical surface from a target shape using interferometric measurement results

A method of measuring a deviation of an optical surface from a target shape comprising:

• generating incoming light having a wave front,
• providing at least two diffractive measurement structures, each configured to adapt part of the wave front to a respective portion of the target shape,
• arranging the diffractive measurement structures relative to each other such that each diffractive measurement structure is traversed by a separate subset of rays of the incoming light,
• illuminating a first region of the optical surface with the incoming light having traversed the diffractive measurement structures and thereby generating first measuring light having interacted with the first region,
• determining the wave front of the first measuring light, designated as a first wave front,
• generating second measuring light having interacted with at least a second region of the optical surface, and determining the wave front of the second measuring light, designated as a second wave front, and
• determining a deviation of the optical surface from the target shape using a stitching algorithm, which stitching algorithm includes determining misalignment components of the at least two diffractive measurement structures based on the first wave front and the second wave front.

A method of measuring a deviation of an optical surface from a target shape comprising:

• generating incoming light having a wave front,
• providing a first wave shaping element and a second wave shaping element, each of the wave shaping elements having a diffractive measurement structure, the diffractive measurement structures being configured for adapting part of the wave front to two distinct portions of the target shape and the first wave shaping element having a diffractive alignment structure,
• aligning the first wave shaping element and the second wave shaping element relative to each other by evaluating alignment light having consecutively interacted with the diffractive alignment structure and with the second wave shaping element,
• illuminating the optical surface with the incoming light having traversed the diffractive measurement structures and thereby generating measuring light having interacted with the optical surface, and
• performing an interferometric measurement by superimposing reference light with at least a portion of the measuring light.