LIGO Document T1100623-x0

Dark Field microscope inspection at Caltech ITM09

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T - Technical notes
1. Defect size
The AR surface of ITM09 was examined using a dark field microscope. The source of the milky appearance is a uniform distribution of very small defects. Most of the defects were not resolvable by this microscope, indicating that they were of order one micrometer or less. Some defects were faint and had a bluish appearance, indicating a size less than half a micrometer.

2. Defect density
Larger defects, of order 2 to 4 micrometers appeared with a density of roughly 30/mm2. The smaller defects had a density ranging from 50x10^3/mm2 to 150x10^3/mm2. There were no areas observed to be free of defects.

3. Out of tolerance
ITM09 does not meet our defect density specification on page 6, LIGO-E0900041-v5
Required: 100 defects inside 120 mm diameter.
or 0.009 defects/mm2.

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