Internal Damage to Optical Glasses with 3 ns-Pulse Laser

The beam of a 3 ns pulse laser (1060 nm) is focussed with a convex lense with 1,1 m focal length. The glass sample to be tested is 20 mm thick: its rear surface has a distance of 100 mm from the focus. The part of the sample which will be shot is illuminated with a Xenon lamp and inspected with a microscope with four fold magnification before and after the shot. In each case a photo is taken.

Two types of internal damage are to be recognized: pointlike damage and threadlike damage. Some glass types show only pointlike damage, even at higher energies (applied energy densities up to 65 J/cm²); other glass types show only threadlike damage caused by self-focussing (dependent to the n2-value). In the most cases both damage types occur but at different levels of energy densities. In BK 1 and BK 7 glass no internal damage is to be seen when applying energy densities up to 65 J/cm².