In some laser cutting processes, there is considerable risk that some portion of the laser beam is reflected at the workpiece and returned into the laser cavity. There, it might disturb laser operation. In order to avoid this problem, a so-called ATFR mirror can be inserted in the beamline. Such a mirror has high reflectance (typically 99%) for s-polarized radiation and low reflectance (typically less than 1%) for p-polarized radiation.