Reactive ion-assisted deposition of e-beam evaporated titanium for high refractive index TiO₂ layers and laser damage resistant, broad bandwidth, high-reflection coatings

Abstract

High-reflection coatings with broad bandwidth can be achieved by pairing a low refractive index material, such as ${\mathrm{SiO}}_2$, with a high refractive index material, such as ${\mathrm{TiO}}_2$. To achieve high refractive index, low absorption ${\mathrm{TiO}}_2$ films, we optimized the reactive, ion-assisted deposition process (${\mathrm{O}}_2$ levels, deposition rate, and ion beam settings) using e-beam evaporated Ti. ${\mathrm{TiO}}_2$ high-index layers were then paired with ${\mathrm{SiO}}_2$ low-index layers in a quarter-wave-type coating to achieve a broader high-reflection bandwidth compared to the same coating composed of ${\mathrm{HfO}}_2/{\mathrm{SiO}}_2$ layer pairs. However, the improved bandwidth exhibited by the ${\mathrm{TiO}}_2/{\mathrm{SiO}}_2$ coating is associated with lower laser damage threshold. To improve the laser damage resistance of the ${\mathrm{TiO}}_2/{\mathrm{SiO}}_2$ coating, we also created four coatings where ${\mathrm{HfO}}_2$ replaced some of the outer ${\mathrm{TiO}}_2$ layers. We present the laser damage results of these coatings to understand the trade-offs between good laser damage resistance and high-reflection bandwidth using ${\mathrm{TiO}}_2$ and ${\mathrm{HfO}}_2$.

© 2013 Optical Society of America

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