Laser induced damage detection on optical coatings via long distance microscope

Kurzfassung

Today’s high power pulsed laser applications need optics with coated surfaces to improve the optical characteristics. A major problem of those layers is the lower laser induced damage threshold (LIDT) compared to the pure substrate. For better understanding of damaging process it is quite necessary to investigate how damages occur. One of these applications are laser systems used in satellites for wind profiling (ADM Aeolus). For best experimental results the testing parameters should be adapted to satellite conditions as good as possible. Therefore all tests are realized in a vacuum chamber under a pressure of 10-9 mbar. Furthermore the expected damage size which wants to be observed is in the range of few microns. This is why a long distance microscope is used in this work to investigate the damage formation online. To show the functionality of system high reflective (coated with ion beam sputtering and electron beam evaporation) and antireflective (coated with ion beam sputtering) coatings are investigated with a repetition rate of 1Hz to acquire images after each pulse. In a next step so called micro pits are investigated in their characteristics and formation. Moreover the dependency of laser repetition rate on LIDT is investigated for rates of 20Hz and 100Hz. A conclusion and an outlook at which possible improvements and new possibilities are discussed complete this work.