To enhance the sensitivity of high-precision measurements based on ultrastable optical cavities such as gravitational-wave detections, achieving low coating mechanical loss is crucial. Nanolaminates have been proposed as potential replacements for the currently used high-refractive-index material ${\mathrm{Ti}\mathrm{O}}_2:{\mathrm{Ta}}_2{\mathrm{O}}_5$. However, due to material selection constraints, nanolaminates inherently face a trade-off between refractive index and optical absorption. Quantized-layer technology offers a promising approach for modifying the optical properties of nanolaminates by introducing quantum effects through reduced well-layer thickness, thereby increasing the optical band gap and suppressing absorption. In this study, we systematically investigate the effects of sublayer thickness on the optical properties and coating mechanical loss of nanolaminates, utilizing a periodic coating structure composed of ${\mathrm{Ti}\mathrm{O}}_2$ and ${\mathrm{Ta}}_2{\mathrm{O}}_5$. By tuning the sublayer thickness and well-layer thickness ratio, we establish general trends linking refractive index, extinction coefficient, optical band gap, Urbach energy, and coating mechanical loss to nanolaminate structural parameters. Notably, when the barrier-layer (${\mathrm{Ta}}_2{\mathrm{O}}_5$) thickness is 3.51 nm and the well-layer (${\mathrm{Ti}\mathrm{O}}_2$) thickness is 1.77 nm, quantized-layer technology enables the fabrication of nanolaminates with a mechanical loss performance superior to that of ${\mathrm{Ti}\mathrm{O}}_2:{\mathrm{Ta}}_2{\mathrm{O}}_5$. Furthermore, we observe a correlation between coating mechanical loss and the short- and medium-range disorder of the atomic structure. This study demonstrates the improvement in room-temperature coating mechanical loss via quantized-layer technology from the perspective of thickness effects.

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• Internal friction
• Light-matter interaction
• Coatings
• Multilayer thin films
• Optical microcavities
• Film deposition
• Gravitational wave detectors
• Precision measurements