Shadowgraphic imaging of metal drilling with a long pulse excimer laser

摘要

A shadowgraphic imaging technique is used for studying the interaction between the laser beam and the material during laser drilling. The used laser is a XeCl excimer laser with a nearly diffraction limited beam and 175 ns pulse length. We studied how and when the material is removed. Holes are drilled with a series of pulses in aluminium and Hastelloy X. The shadowgraphic images show the development of a Shockwave whose expansion is in agreement with theory. Both the removal of material at different times after the start of the laser pulse and the material removal for different pulses during the drilling process are shown. Material removal occurs by vaporisation as well as melt ejection. Our experiments show the same amount of removed material for drilling with different cover gases. The shadowgraphic images show that the larger part of the material is removed after the end of the laser pulse.