A machining head for laser cutting of a workpiece , having a first interface for a machining laser source for emitting a machining laser beam ; a second interface for an illumination light source for emitting a linearly polarised illumination light beam ; an exit opening for the machining laser beam and the illumination light beam ; a third interface for a detector device for detecting the illumination light beam reflected from the workpiece ; and guide optics for at least partial coaxial guiding of the emitted illumination light beam through the exit opening and of the illumination light beam reflected from the workpiece , through the exit opening , to the third interface ; the guide optics (116; 117) having a polarising beam splitter for guiding at least part of the emitted linearly polarised illumination light beam in the direction of the exit opening ; and a retardation plate arranged between the polarising beam splitter and the exit opening , for converting at least a portion of the emitted linearly polarised illumination light beam into a circularly polarised illumination light beam and for converting at least a portion of the circularly polarised illumination light beam reflected from the workpiece into a linearly polarised illumination light beam ; wherein a machining laser optics arranged between guide optics and exit opening is provided; wherein the retardation plate is the optical element of the guide optics closest to the exit opening ; and characterised in that in the guide optics at least one optical element for collimating and/or focusing the illumination light beam is positioned between the retardation plate and the polarising beam splitter . a first interface for a machining laser source for emitting a machining laser beam ; a second interface for an illumination light source for emitting a linearly polarised illumination light beam ; an exit opening for the machining laser beam and the illumination light beam ; a third interface for a detector device for detecting the illumination light beam reflected from the workpiece ; and guide optics for at least partial coaxial guiding of the emitted illumination light beam through the exit opening and of the illumination light beam reflected from the workpiece , through the exit opening , to the third interface ; the guide optics (116; 117) having a polarising beam splitter for guiding at least part of the emitted linearly polarised illumination light beam in the direction of the exit opening ; and a retardation plate arranged between the polarising beam splitter and the exit opening , for converting at least a portion of the emitted linearly polarised illumination light beam into a circularly polarised illumination light beam and for converting at least a portion of the circularly polarised illumination light beam reflected from the workpiece into a linearly polarised illumination light beam ; wherein a machining laser optics arranged between guide optics and exit opening is provided; wherein the retardation plate is the optical element of the guide optics closest to the exit opening ; and characterised in that in the guide optics at least one optical element for collimating and/or focusing the illumination light beam is positioned between the retardation plate and the polarising beam splitter . <EOS>