Optimized metrology for laser-damage measurement: application to multiparameter study

An automatic test apparatus for refined testing of laser damage is presented that permits an in situ analysis of the tested area before, during, and after pulsed irradiation. Spatial and temporal beam profiling are performed in real time and give access to the localized fluence for each shot. Furthermore, an optimization of the initiation of damage detection is undertaken by use of image processing and yields a resolution better than 1 microm. Through several examples, these conditions are demonstrated to be useful for reaching an understanding of the laser-damage process. A complete study is undertaken of different kinds of glass that permits the main influence of test parameters (shot frequency, shot number, beam profile variation, temporal and spatial meshing, ...) on the damage procees to be shown. The study was made for different test procedures (1:1, S:1, R:1) and completed by atomic-force microscope analysis. Evidence indicates that the upgrading of metrology associated with an automatic process offers new opportunities for understanding laser-induced damage mechanisms and for emphasizing specific effects such as damage initiation, damage growth, and conditioning for repetitive shots.