The method involves local removal to form blind holes arranged in a row and separated by struts using a pulsed laser beam. The line is formed by moving the material and the laser beam w.r.t. each other. The laser light transmitted through each blind hole is measured after each pulse and the detector signal (1.1) integrated after each detection. The integral is compared with a desired value defined for each blind hole and correlated with the desired residual wall thickness. The laser is switched off when the desired thickness is reached. The process is repeated for the struts to complete the line.
