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  4. The exceptional stability required from high finesse optical cavities and high precision interferometers is fundamentally limited by Brownian motion noise in the interference coatings of the cavity mirrors. In amorphous oxide coatings these thermally driven fluctuations are dominant in the high index layer compared to those in the low index SiO2layer in the stack. We present a systematic study of the evolution of the structural and optical properties of ion beam sputtered TiO2-doped Ta2O5films with annealing temperature. We show that low mechanical loss in TiO2-doped Ta2O5with a Ti cation ratio = 0.27 is associated with a material that consists of a homogeneous titanium-tantalum-oxygen mixture containing a low density of nanometer sized Ar-filled voids. When the Ti cation ratio is 0.53, phase separation occurs leading to increased mechanical loss. These results suggest that amorphous mixed oxides with low mechanical loss could be identified by considering the thermodynamics of ternary phase formation.

     
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  5. Amorphous tantala (Ta2O5) thin films were deposited by reactive ion beam sputtering with simultaneous low energy assistAr+orAr+/O2+bombardment. Under the conditions of the experiment, the as-deposited thin films are amorphous and stoichiometric. The refractive index and optical band gap of thin films remain unchanged by ion bombardment. Around 20% improvement in room temperature mechanical loss and 60% decrease in absorption loss are found in samples bombarded with 100-eVAr+. A detrimental influence from low energyO2+bombardment on absorption loss and mechanical loss is observed. Low energyAr+bombardment removes excess oxygen point defects, whileO2+bombardment introduces defects into the tantala films.

     
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  6. We present the optical and structural characterization of films ofTa2O5,Sc2O3, andSc2O3dopedTa2O5with a cation ratio around 0.1 grown by reactive sputtering. The addition ofSc2O3as a dopant induces the formation of tantalum suboxide due to the “oxygen getter” property of scandium. The presence of tantalum suboxide greatly affects the optical properties of the coating, resulting in higher absorption loss atλ<#comment/>=1064nm. The refractive index and optical band gap of the mixed film do not correspond to those of a mixture ofTa2O5andSc2O3, given the profound structural modifications induced by the dopant.

     
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