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Micrometer resolved inspection of defects and laser damage sites in UV high-reflecting coatings by photothermal displacement microscopy

: Kaiser, N.; Bodemann, A.; Reichling, M.; Welsch, E.

Journal de physique. 4, Colloque 4 (1994), Juillet, pp.C7.611-C7.614
ISSN: 1155-4339
Journal Article
Fraunhofer IOF ()
Dünne optische Schicht; excimer laser optics; Excimer-Laser-Optik; fluoride thin films; Fluoridschicht; laser induced damage threshold; Laserzerstörschwelle; optical coating; optical thin films; oxide thin films; Oxidschicht; ultraviolet spectral region; ultravioletter Spektralbereich; UV

Characteristic features of defects in dielectric multilayer UV-mirrors are determined by photothermal displacement imaging. A large number of micron sized absorbing defects are detected, however, their size and absorption strength distribution strongly depends on thin film preparation conditions. It is found that all features well correlate with thin film damage thresholds at 248 nm. An enhanced photothermal amplitude in a halo around ablation spots damaged by high fluence UV light indicates thin film delamination resulting from thermoelastic stress during laser irradiation.