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 (116, 117) 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 (116, 117) 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.