The invention relates to a method for determining at least one unknown laser beam parameter of a laser beam used for correcting errors of a transparent material including inducing a first persistent modification in the material by an interaction with the laser beam having a first set of laser beam parameters, measuring the induced first persistent modification of the material, calculating a second persistent modification in the material using a model describing persistent modifications in the material with a second set of laser beam parameters, wherein the first set of laser beam parameters comprises the second set of laser beam parameters and the at least one unknown laser beam parameter, setting up a target functional including the first persistent modification and the second persistent modification, and determining the at least one unknown laser beam parameter by minimizing the target functional.