Extending the boundaries of ultraviolet-visible meta-optics via direct imprinting of tantalum pentoxide composite

Broadband metasurfaces capable of precise electromagnetic wave control from the ultraviolet (UV) to the visible range enable applications such as multispectral imaging, secure multi-band optical encryption, and multi-spectral microscopy. However, realizing scalable UV-visible broadband metasurfaces remains challenging due to the subwavelength critical dimensions and high aspect ratios required for UV operation, which are difficult to fabricate reliably using conventional lithography. These difficulties are further compounded by the intrinsic trade-off between refractive index and absorption in dielectric materials such as TiO₂ and SiC, which exhibit strong UV absorption. Here, we introduce a scalable nanoimprint lithography (NIL) platform based on tantalum pentoxide (Ta₂O₅) particle-embedded resin (PER) that overcomes these material and fabrication limitations. The Ta₂O₅ PER exhibits a refractive index of 1.9 at 300 nm and maintains a relatively high refractive index with negligible absorption across the visible range. This material is also compatible with diverse meta-atom geometries. Using this approach, we fabricated a broadband metahologram and a hyperbolic phase metalens. Electromagnetic simulations predict conversion and focusing efficiencies approaching 80% at 320 nm, and experimental validation yielded 64% conversion efficiency for the metahologram and 61.3% focusing efficiency for the metalens. The metasurfaces consistently reconstruct designed images across 320-635 nm, confirming broadband operation. This one-step direct patterning enabled high aspect ratio without additional deposition or etching processes. This provides a practical route toward scalable, high-performance metasurfaces spanning the UV-visible spectrum.