Material processing apparatus and method for preparing a material processing apparatus

A method for preparing a material processing apparatus for material processing by generating optical breakthroughs in or on an object, which comprises a variable, three-dimensionally acting focus adjusting device for focusing processing laser radiation on various locations in or on the object,

• wherein a contact element to be fitted onto the object is attached to the material processing apparatus, wherein the contact element is transparent to the processing laser radiation, comprises a contact surface on its side to be fitted onto the object, and an entry surface for the processing laser radiation on its side facing the material processing apparatus,
• wherein a shape of the contact surface and/or entry surface is determined by means of radiation of measurement laser radiation onto the contact surface and/or entry surface before the processing of the object, in that the measurement laser radiation is focused near or on the contact surface and/or entry surface by means of the variable focus adjusting device, wherein an energy density of the focused measurement laser radiation is too low for generating an optical breakthrough,
• wherein radiation backscattered or back-reflected from the focus of the measurement laser radiation is confocally detected,
• wherein a position of intersections on the contact surface and/or entry surface is determined from the confocally detected radiation and the associated adjustment of the variable focus adjusting device, and
• wherein a three-dimensional surface model is adapted to the determined position of the intersections, wherein the three-dimensional shape of the contact surface and/or of the entry surface is provided by the surface model.