Abstract: A welding method and device for joining first and second workpieces using a high-energy machining beam. The method comprising inserting the first workpiece into a workpiece holder; positioning the second workpiece on a top side of the first workpiece at a target position for joining the workpieces; providing a high-energy machining beam, and focusing the machining beam on a current machining area; generating a measuring beam in an optical coherent tomograph, the measuring beam being coupleable into the machining beam; carrying out a process measurement by the measuring beam in the current machining area during machining of the workpieces; carrying out a control measurement by the measuring beam on at least one of the workpieces; and determining a distance between the first and second workpieces for detecting a gap between the workpieces, based on the result of the control measurement.