Low loss dielectric mirrors for optical cavities applications
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Cavity-based single-photon emitters possess great potential in many quantum applications. Fabry-Perot cavities are an especially good candidate for these applications in order to provide the high-Q cavities necessary for efficient coupling. To assure strong coupling in the cavity, very high reflectance dielectric mirrors are required. Achieving this means overcoming several technical challenges in order to minimize the optical losses in the dielectric layers. This research work explores the potential of several dielectric materials and physical vapour deposition methods to fabricate high reflectance mirrors in the visible region. Single layer material characterisation results showed extinction coefficients below 10-5 and a surface roughness below 1 nm for metal oxides deposited by ion assisted and plasma assisted processes. A reflectance superior to 99.9 % was obtained for TiO2/SiO2, ZrO2/SiO2 and Nb2O5/SiO2 multilayer mirrors deposited using ion assisted E-beam, plasma assisted and microwave assisted sputtering methods. A surface roughness of 0.3 to 0.5 nm was obtained for ZrO2/SiO2 and Nb2O5/SiO2 multilayer mirrors deposited using plasma assisted and microwave assisted sputtering methods. Scatter losses of 200 ppm were obtained for TiO2/SiO2 deposited using ion assisted E-beam deposition. Micron sized TiO2/SiO2 and ZrO2/SiO2 mirrors were achieved on curved glass templates by Ion assisted E-beam deposition.