Method for measuring spacing by means of OCT for focus control of laser-processed material and associated computer program product

The invention relates to a method for measuring a distance by means of an optical coherence tomography device (4), the measuring beam (5, 5 ') of which is directed towards a workpiece surface (11) by means of laser machining optics (7), in particular by means of scanner optics. The method comprises the following method steps: (a) measuring a focal distance (A) between a z-focal position (F) of a machining laser beam (3) directed through the laser machining optics (7) towards the reference surface (10) and the reference surface (10), and measuring a reference distance (L0) between a reference arm mirror (16) of the optical coherence tomography device (4) and the reference surface (10) by means of a measuring beam (5) directed to the same point (P1) of the reference surface (10) as the processing beam (3) or directed to a point (P2) of the reference surface (10) next to the incidence point (P1) of the processing beam (3); (b) measuring a workpiece distance (L1) between the reference arm mirror (16) and the work