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We report on thermal noise from the internal friction of dielectric coatingsmade from alternating layers of Ta2O5 and SiO2 deposited on fused silicasubstrates. We present calculations of the thermal noise in gravitational waveinterferometers due to optical coatings, when the material properties of thecoating are different from those of the substrate and the mechanical loss anglein the coating is anisotropic. The loss angle in the coatings for strainsparallel to the substrate surface was determined from ringdown experiments. Wemeasured the mechanical quality factor of three fused silica samples withcoatings deposited on them. The loss angle of the coating material for strainsparallel to the coated surface was found to be (4.2 +- 0.3)*10^(-4) forcoatings deposited on commercially polished slides and (1.0 +- 0.3)*10^{-4} fora coating deposited on a superpolished disk. Using these numbers, we estimatethe effect of coatings on thermal noise in the initial LIGO and advanced LIGOinterferometers. We also find that the corresponding prediction for thermalnoise in the 40 m LIGO prototype at Caltech is consistent with the noise data.These results are complemented by results for a different type of coating,presented in a companion paper.Comment: Submitted to LSC (internal) review Sept. 20, 2001. To be submitted to  Phys. Lett.

Thermal noise in interferometric gravitational wave detectors due to dielectric optical coatings