Device and method for determining a focal point

Abstract

The invention relates to a beam analysis device () for determining the axial position of the focal point () of an energy beam or a sample beam () decoupled from an energy beam, comprising a beam-shaping device (), a detector (), and an analysis device (). The beam-shaping device () is designed to release two sub-beams () from the sample beam () on a plane of the sub-beam release process (). The cross-sections of the two sub-beams () are defined by sub-apertures () which are delimited from each other and which are arranged at a distance k to each other in a first lateral direction (). The beam-shaping device () is designed to image the two sub-beams () in order to form two beam spots () on the detector and deflect at least one of the two sub-beams () in a second lateral direction () which is oriented transversely to the first lateral direction () in order to form a distance w in the second lateral direction () between the two beam spots (). The analysis device () is designed to determine the distance a along the first lateral direction () between positions of the two beam spots () on the detector () and to determine the axial position of the beam focus () on the basis of the distance a and/or to determine a change in the axial position of the beam focus () on the basis of a change in the distance a. The invention also relates to a corresponding method for determining the axial position of a beam focus ().