High-efficiency metasurfaces down to the vacuum ultraviolet region

Ultraviolet (UV) metasurfaces provide a promising approach for complex wavefront manipulation through sub-wavelength modulation of amplitude, phase, and polarization. However, the fabrication of UV metasurfaces faces challenges arising from material limitations and intricate processing requirements, leading to a decline in optical field manipulation performance, as well as lower transmittance and polarization conversion efficiency. In this work, a two-step fabrication strategy is proposed to fabricate metasurfaces that simultaneously achieve excellent optical field manipulation performance, high transmittance, and high polarization conversion efficiency in the UV band. The process involves femtosecond laser direct writing to induce birefringent nanopores in fused silica for geometric-phase modulation. This is followed by thermal annealing to eliminate defect-induced absorption centers, which significantly enhances transmittance. As a proof of concept, two metasurfaces were fabricated and characterized to demonstrate the strategy's effectiveness across a broad UV spectral range. A 193nm holographic element, operating in the vacuum-UV band, achieved 67% transmittance and 72% polarization conversion efficiency. In parallel, a 355nm radial polarization beam generator, operating in the near-UV band, showcased excellent performance, exhibiting 90% transmittance and 89% polarization conversion efficiency. This fabrication strategy shows promise for a wide range of applications, such as high-resolution lithography, holography, and quantum optical systems.