Damage Threshold Testing of Laser Optics

The Institute of Technical Physics at the DLR in Stuttgart is operating a qualification laboratory where the laser vulnerability of optical components can be tested under pulsed irradiation and for operation at high power or in space. Therefore, standardized damage threshold tests are performed, supplemented by raster scans across large areas. Another field of activity is laserinduced contamination. Furthermore, conversion efficiency and radiation resistance of non-linear crystals are investigated. These tests are also provided as a service for external customers. Damage threshold tests are carried out in an application-oriented manner and at common laser wavelengths in the IR (1064 nm), visible (532 nm), and UV (355 nm) spectral range and with pulse lengths of a few nanoseconds. Tests are performed mostly in multipulse mode according to ISO 21254. The results of the multipulse tests can be used for scaling of damage thresholds to very large pulse numbers or very long irradiation times. Various types of optics with different coating designs (e.g. antireflective or high-reflective coatings) can be handled in the setup at different angles of incidence. But also other optical components, for example, thindisk laser modules have been already successfully tested. The tests can be performed at the DLR laboratory under ambient conditions or optionally under artificial gas atmosphere and vacuum conditions. The extension to vacuum testing was due to the ongoing requests of european companies and European Space Agency (ESA) for vacuum laser optics qualification in view of upcoming space-laser missions. Such long term operations of laser systems in space with a mission duration of several years lead to very stringent requirements of precision and longevity of utilized optical components.