Damage assessment and possible damage mechanisms to 1-meter diameter Nova turning mirrors
Abstract
A major concern in the operation of the LLNL 120 kJ Nova laser system is damage to the nominal l-meter diameter mirrors (i.e., HR coatings). The damage appears to originate from microscopic defects that vary in size up to approximately 30 (mu)m in diameter. These defects produce damage sites up to 250 microns and, in some cases, covering 20 percent or more of the mirror surface. Defects due to particulates that are in or under the coating are highly unlikely due to the fact that coating thickness is only 5 microns thick and particles up to 30 microns would produce surface roughness that could be easily detected. Consequently, the defects must be plate-like (i.e., 2-D) in nature. A by-product of the damage is a haze left on the surface of the mirror. This haze is analyzed and shown to be blown-off particles of ZrO2/SiO2 coating material. The particle morphology suggests nucleation from a vapor phase which implies localized heating in the coating to temperatures on the order of 3000 K. Some possible damage mechanisms are also explored.
- Publication:
-
Presented at the 1989 Boulder Damage Symposium
- Pub Date:
- August 1990
- Bibcode:
- 1990boda.symp....1E
- Keywords:
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- Antireflection Coatings;
- Damage;
- Damage Assessment;
- Energy Transfer;
- Mirrors;
- Nova Laser System;
- Degradation;
- Reflectance;
- Silicon Oxides;
- Temperature Effects;
- Zinc Oxides;
- Lasers and Masers