The surface morphology of as-deposited and laser-damaged dielectric mirror coatings studied in situ by atomic force microscopy
Atomic force microscopy was used to determine in situ the nm-scale morphological changes that occur on dielectric optical coatings as a result of laser-induced damage. The optical film studied was a highly reflective dielectric multilayer mirror (HR) consisting of many alternating HfO{sub 2} and SiO{sub 2} layers of quarter-wave thickness at 1.06 {mu}m. The top layer was a {lambda}/2 SiO{sub 2} overcoat. Laser beam specifications were: 1.06 {mu}m wavelength, 8 ns pulselength, and 110 {mu}m to 300 {mu}m beam diameter. The laser fluence was determined by beam profiling and total energy measurements. The maximum scan-range of the AFM was 80 {mu}m. A survey of the as-deposited surface shows mostly hillocks of approximately 200 nm width and 10 nm height. Comparison of this hillock structure to that of a single layer of SiO{sub 2} and a surface layer of HfO{sub 2} was made. Irregularities (i.e. defects) on the surface of the HR consisted of {mu}m-scale domes, and occasional craters, of {mu}m planar dimension and depth extending over many layers. Three types of coating defects were identified which could be related to the classic nodule-type coating defect. Nodule defects were found to be easily ejected from the coating surface by laser illumination, leaving craters from which further damage would propagate. After laser damage with fluences above 30 J/cm{sup 2} the hillocks coalesced into structures with heights and widths 5--10 times that of the as-deposited film. A pattern of concentric surface distortions appeared at higher fluences, in some cases following the full circumference of the beam. 14 refs., 9 figs.
- Research Organization:
- Lawrence Livermore National Lab., CA (United States)
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 5306892
- Report Number(s):
- UCRL-JC-108077; CONF-9107115-21; ON: DE91016571
- Resource Relation:
- Conference: Society of Photo-Optical Instrumentation Engineers (SPIE) meeting, San Diego, CA (United States), 21-26 Jul 1991
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
36 MATERIALS SCIENCE
LASER MIRRORS
DAMAGE
REFLECTIVE COATINGS
LASER RADIATION
PHYSICAL RADIATION EFFECTS
DIELECTRIC MATERIALS
HAFNIUM OXIDES
MICROSCOPY
SILICON OXIDES
SURFACE COATING
THIN FILMS
CHALCOGENIDES
COATINGS
DEPOSITION
ELECTROMAGNETIC RADIATION
FILMS
HAFNIUM COMPOUNDS
MATERIALS
MIRRORS
OXIDES
OXYGEN COMPOUNDS
RADIATION EFFECTS
RADIATIONS
REFRACTORY METAL COMPOUNDS
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
656003* - Condensed Matter Physics- Interactions between Beams & Condensed Matter- (1987-)
360206 - Ceramics
Cermets
& Refractories- Radiation Effects