Parallel Use of Detection Channels for LIDT-Testing in the UV-Range

摘要

The reliable online detection of damage events is a very important part in the measurement of multi-pulse laser-induced damage thresholds (LIDT) of optical components, In many measurement protocols, a certain threshold for radiation scattered-by the test site is defined as damage criterion. Nevertheless, for example in the measurement of uncoated substrates or antireflective coatings online damage detection on the basis of scattering is often observed to be of less consistency. In such cases accumulation effects over a large number of pulses may appear and eventually result in a catastrophic failure of the optic before a significant indication of the scatter detector. As a consequence, valuable information on the nature of the damage may be lost. In this paper the use of online reflectance- and transmittance-measurements as a different kind of switch-off criterion for LIDT-measurements is considered. The measurements are performed at 266nm using a Q-switched ns-laser-source. Advantages and disadvantages of the detection system are discussed and compared to a typical online scatter detection system. Slight changes in reflectance and transmittance might be used as a pre-indicator of a catastrophic failure of the optic and may allow for an interpretation of LIDT-measurements in the context of lifetime testing.