Bulk LIDT variances of fused silica: a material developer's perspective

Fused silica an optical material of choice for high energy laser applications offers a wide range of advantages in the UV and NIR wavelength range. Increasing laser performance (especially with critical fluences) require detailed information on laser induced damage threshold of the optical material itself, and not just the coating. Therefore, S-on-1 measurements according to ISO 21254-2 were commissioned from two different, experienced, and well-respected laboratories. The resulting LIDT (laser induced damage threshold) values are discussed in the context of current publications and differences are worked out. The measurements focus on the ns-pulse regime at 1064 and 355nm. The results differ up to a factor of 10 between different laboratories. In comparison to the literature study, we noticed a spread of measured values around a factor of 20. Non-binding recommendations of the standard as well as the optical setup have significant influence on the obtained LIDT values. However, depending on the optical design of the application, one or the other optical setup with the corresponding LIDT value can be relevant. In this respect there is no such thing as a single, generally applicable value. Nevertheless, a standard should enable material comparisons under sufficiently standardized conditions.