Abstract: A type of "light barrier" is used to monitor the functionality of the transparent protective element (5) of a transparent laser optical system: additional light (15) is coupled into a lateral surface of the protective element (5) at an angle which deviates from the incidence direction of the laser beam (1, 2). Said light traverses the material of the protective element (5) and then exits again via the lateral surface, where it is detected by a light detector (16). Cracks and fractures of the protective element (5) can be detected by a change in the light received in the light detector (16). If appropriate, this measurement is supplemented by the measurement of the temperature difference between inflowing and outflowing cooling water, as well as by radiation temperature sensors (14) which monitor the local temperature distribution in the protective element (5).

Abstract: The quality of a weld is usually monitored via the different wavelength radiation issuing from the weld point. During the welding of workpieces, however, this radiation (S) is also modulated by the instantaneous width (b) of the gap existing between the workpieces. To avoid the generation of unnecessary fault signals (F) on the one hand and excessive tolerance bands for the permitted signal range on the other hand, the invention proposes that a correction formula (.increment.S(B)) which reproduces the dependency of the radiation signals (S) on the gap width (B) be produced in a preliminary test. The gap width (B) in the weld point is defined during welding. A correction value (.increment.S(B)) is defined during the welding process on the basis of the correction formula (.increment.S(B)) and the instantaneous gap width (B) in the weld point and the limit values (MAx(B.sub.0), MIN(B.sub.0) previously defined for a gap width zero are displaced by this correction value (.increment.S(B)).

Abstract: A device for machining a workpiece, for example by welding or cutting, a machining laser beam which passes through a channel in a laser machining head. An observation channel is provided in the laser machining head through which rays from the workpiece pass. A component of the rays from a specific geometrical region of the workpiece is deflected through the observation channel to a detector mounted on the laser machining head.