In situ atomic force microscopy of laser-conditioned and laser- damaged HfO sub 2 /saw sub 2 dielectric mirror coatings

Conference · Mon Jan 07 04:00:00 EST 1991

OSTI ID:5689477

Staggs, M C; Balooch, M; Kozlowski, M R; Siekhaus, W J

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 illumination. Of particular interest is a process called laser conditioning in which the damage threshold of the films is increased by a factor of 2 to 3 when the film is first illuminated at fluences below the damage threshold. The optical coating studied was a highly reflective dielectric multilayer mirror (HR) consisting of many alternating quarter-wave layers of HfO{sub 2} and SiO{sub 2} 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- to 10-ns pulsewidth. Laser beam spot sizes ranging from 85 {mu}m to 1.4 mm in diameter. The maximum scan range of the AFM was 80 {mu}m. A survey of the as-deposited surface shows mostly hillocks approximately 200 nm in diameter and 10 nm in height. The predominant surface irregularity is {mu}m-scale domes associated with well known nodule defects. Laser illumination causes nodule defects to be easily ejected from the coating surface. Further damage may propagate from the resulting craters. These nodule defects therefore determine the damage threshold of the film. Using the AFM we have shown that for illumination at fluences below the nodule ejection threshold we observe a decrease in the surface roughness of the nodule defects and hillock structure of the as-deposited film. The subtle changes in these surface features may be an indication that the film is being mechanically stabilized, thus providing the observed conditioning effect.

• Research Organization: Lawrence Livermore National Lab., CA (United States)
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5689477
• Report Number(s): UCRL-JC-108274; CONF-911064--7; ON: DE92008079
• Country of Publication: United States
• Language: English

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