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  4. Photothermal microscopy of defects and laser damage morphology in Al2O3/SiO2 dielectric mirror coatings for 248 nm
 
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1994
Conference Paper
Title

Photothermal microscopy of defects and laser damage morphology in Al2O3/SiO2 dielectric mirror coatings for 248 nm

Abstract
The cw photothermal displacement technique (PDT) has been shown to be a useful tool for the characterisation of optical coatings with high lateral resolution combined with an ultrahigh sensitivity. By micrometer resolved PDT-measurements on Al2O3/SiO2 multilayer coatings we found that the non-damaged thin film systems contain a great amount of photothermal inhomogeneities (defects) with lateral sizes ranging from several mu m that are not visible by optical microscopy. In most cases these areas of strongly enhanced displacement response originate from microdelamination, decreased thermal impedance at the film interface or absorption centers. Thermal inhomogeneities in the film normally play a minor role. The measured damage thresholds of various mirrors correlate with both the defect concentration and the PDT background signal. Furthermore, the damage morphology has been investigated by photothermal measurements and photothermal inages were compared to results from scanning electron mi croscopy. Areas with enhanced thermal impedance in the surroundings of some damage spots are attributed to lacal microdelamination within the film systems, indicating the onset of laser damage (pre-damage).
Author(s)
Kaiser, N.
Reichling, M.
Bodemann, A.
Welsch, E.
Mainwork
Laser-Induced Damage in Optical Materials 1993. Proceedings  
Conference
Laser-Induced Damage in Optical Materials Symposium 1993  
Annual Boulder Damage Symposium 1993  
Annual Symposium on Optical Materials for High-Power Lasers 1993  
Language
English
Fraunhofer-Institut für Angewandte Optik und Feinmechanik IOF  
Keyword(s)
  • 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

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