Method for beam analysis in an EUV laser plasma source of a microlithographic projection exposure apparatus, - wherein a plurality of beam parameters of a laser beam, which was generated by a laser light source in the EUV laser plasma source and which propagates along an optical axis, are ascertained for analysing geometric beam parameters and wavefront deviations, - wherein this plurality of beam parameters comprises at least one of the parameters of beam size, beam decentration, beam inclination, beam divergence, astigmatism, coma, spherical aberration, and wherein the method includes the following steps: a) splitting the laser beam into a plurality of partial beams, which have a focal offset in the longitudinal direction with respect to the optical axis; b) recording a measurement image generated by these partial beams, which has spot images corresponding to different focal positions; c) performing a forward simulation of the laser beam in the EUV laser plasma source on the basis of estimated start values for the beam parameters in order to obtain a simulated image; and d) calculating a set of values for the beam parameters on the basis of a comparison between the simulated image and the measurement image; e) performing steps c) and d) iteratively, wherein the respectively calculated values for the beam parameters form the basis of a respective subsequent forward simulation; and f) outputting output values for the beam parameters ascertained by the iteration in step e). - wherein a plurality of beam parameters of a laser beam, which was generated by a laser light source in the EUV laser plasma source and which propagates along an optical axis, are ascertained for analysing geometric beam parameters and wavefront deviations, - wherein this plurality of beam parameters comprises at least one of the parameters of beam size, beam decentration, beam inclination, beam divergence, astigmatism, coma, spherical aberration, and wherein the method includes the following steps: a) splitting the laser beam into a plurality of partial beams, which have a focal offset in the longitudinal direction with respect to the optical axis; b) recording a measurement image generated by these partial beams, which has spot images corresponding to different focal positions; c) performing a forward simulation of the laser beam in the EUV laser plasma source on the basis of estimated start values for the beam parameters in order to obtain a simulated image; and d) calculating a set of values for the beam parameters on the basis of a comparison between the simulated image and the measurement image; e) performing steps c) and d) iteratively, wherein the respectively calculated values for the beam parameters form the basis of a respective subsequent forward simulation; and f) outputting output values for the beam parameters ascertained by the iteration in step e). a) splitting the laser beam into a plurality of partial beams, which have a focal offset in the longitudinal direction with respect to the optical axis; b) recording a measurement image generated by these partial beams, which has spot images corresponding to different focal positions; c) performing a forward simulation of the laser beam in the EUV laser plasma source on the basis of estimated start values for the beam parameters in order to obtain a simulated image; and d) calculating a set of values for the beam parameters on the basis of a comparison between the simulated image and the measurement image; e) performing steps c) and d) iteratively, wherein the respectively calculated values for the beam parameters form the basis of a respective subsequent forward simulation; and f) outputting output values for the beam parameters ascertained by the iteration in step e).