Device and method for determining a focal point

A beam analysis device (10) for determining an axial position of a beam focus (71), wherein

• the beam focus (71) is a focus (76) of an energy beam (77) of electromagnetic radiation, or a focus of a sample beam (70) decoupled from the energy beam (77), comprising a beam shaping device (12), a detector (40), and an evaluation device (45);
• wherein
• the beam shaping device (12)
• is set up to release two sub-beams (72, 73) from the energy beam (77), or from the sample beam (70) decoupled from the energy beam (77), in a plane of the sub-beam release (19), wherein
• the two sub-beams (72, 73) are a first sub-beam (72) and a second sub-beam (73), wherein
• cross-sections of the two sub-beams (72, 73) in the plane of the sub-beam release (19) are defined by a respective sub-aperture (32, 33), wherein
• the sub-apertures (32, 33) are delimited from one another, and centre points of the sub-apertures (32, 33) are located at a distance k from one another, wherein
• a first lateral direction (31) is defined by the distance k of the sub-apertures (32, 33), wherein
• the term “lateral” refers to directions in planes at right angles to the respective local optical axis (11),
• is set up to form an intensity distribution (83) on the detector (40) with beam spots (92, 93), and to form at least one beam spot (92) from the first sub-beam (72) and at least one beam spot (93) from the second sub-beam (73), to image the two sub-beams (72, 73) onto the detector (40) and to deflect and/or offset at least one of the two sub-beams (72, 73) in a second lateral direction (37) so as to form a distance w along the second lateral direction (37) between two beam spots (92, 93) on the detector (40), wherein
• the second lateral direction (37) is aligned transversely to the first lateral direction (31), and wherein
• the two beam spots (92, 93) are the at least one beam spot (92) of the first sub-beam (72) and the at least one beam spot (93) of the second sub-beam (73);
• wherein
• the detector (40)
• comprises a light radiation-sensitive sensor, resolving spatially in two dimensions, which is set up to convert the intensity distribution (83) impinging on the detector (40) into electrical signals, and
• is arranged along a propagation path for the two sub-beams (72, 73) at a distance s behind the plane of the sub-beam release (19);
• and wherein
• the evaluation device (45)
• is set up to process the electrical signals of the detector (40), which represent the intensity distribution (83) on the detector (40),
• is set up to determine a distance a along the first lateral direction (31) between positions of the two beam spots (92, 93) on the detector (40), and
• is set up to determine an axial position of the beam focus (71) based on the distance a, and/or to determine an alteration in the axial position of the beam focus (71) based on an alteration in the distance a.