Double-mirror shear interferometer

A method for non-destructive interferometric measurement of a surface of an object, the method comprising:

• providing a measuring arrangement comprising:
• a diaphragm having an aperture,
• a mirror arrangement arranged downstream of the diaphragm in a beam direction and comprising a partially transparent partial mirror and a full mirror arranged behind the partial mirror in the beam direction,
• a camera lens, and
• a camera comprising a camera chip having a maximum local sampling frequency;
• illuminating the surface of the object with coherent light;
• receiving light reflected from the surface as an incident light beam and guiding the incident light beam through the diaphragm;
• diffracting the incident light beam at the diaphragm before the incident light beam impinges on the mirror arrangement;
• splitting the incident light beam at the mirror arrangement into
• a first partial beam reflected at the partial mirror, and
• a second partial beam transmitted through the partial mirror and reflected at the full mirror;
• directing the first and second partial beams toward the camera such that the first and second partial beams propagate non-collinearly toward the camera and interfere at the camera;
• rotating one of the mirrors of the mirror arrangement relative to the other mirror such that the mirrors enclose a non-zero angle β in a plane normal to mirror surfaces of the mirrors;
• reflecting the incident light beam toward the camera at an angle α of at least 70° at at least one of the mirrors;
• spacing mirror surfaces of the mirrors apart by a distance x, wherein the distance x is greater than or equal to 70% of a width of the aperture of the diaphragm and less than seven times the width of the aperture;
• dimensioning the diaphragm such that diffraction of the incident light beam at the diaphragm limits a spatial frequency of light incident on the camera chip to at most the maximum local sampling frequency of the camera chip during detection;
• recording, by the camera, an interferometric superposition of the first and second partial beams;
• and
• evaluating the recorded interferometric superposition to determine at least one measurement variable characteristic of the surface of the object.