Apparatus and method for characterizing a microlithographic mask

The invention relates to an apparatus and a method for characterizing a microlithographic mask. According to one aspect, an apparatus according to the invention comprises at least one light source (105, 205, 405a, 405b, 605) which emits coherent light, an illumination optical unit (110, 210, 310, 311, 410, 510, 610, 710, 810) which produces a diffraction-limited light spot on the mask (120, 220, 620, 720) from the coherent light of the at least one light source, a scanning device, by means of which it is possible to implement a scanning movement of the diffraction-limited light spot relative to the mask, a sensor unit (130, 230, 630, 730, 830), and an evaluation unit for evaluating the light that is incident on the sensor unit and has come from the mask, an output coupling element (140, 240, 340) for coupling out a portion (145, 245) of the coherent light emitted by the at least one light source, and an intensity sensor (150, 250) for capturing the intensity of this output coupled portion.