A device for processing material of a workpiece, the device including a pulsed processing laser, a focusing lens, a beam-deflection unit, a control unit and a confocal detector unit. The intensity of the laser radiation is variable. An imaging unit is provided to detect structures within the workpiece using electromagnetic radiation, wherein the electromagnetic radiation of the imaging unit is radiated via the beam-deflection unit and the focusing lens into the workpiece, and evaluating device is provided and compares the position of the focus of the laser radiation determined by the detector unit with the expected position of the focus in the image of the workpiece obtained by the imaging unit.