High Numerical Aperture Metalens for the Deep Ultraviolet

Deep-ultraviolet (DUV) radiation is essential for advanced nanofabrication, biomedical imaging, and emerging photonic technologies, yet the absence of compact, high-performance optical components in this spectral range has impeded progress. We demonstrate an aluminum nitride (AlN) metalens with record-high numerical aperture (HNA) from 0.9 to 0.7, operating at 266 nm. Optical measurements confirm diffraction-limited focusing performance. Importantly, we show a direct laser writing microscopy (DLWM) that lithographic direct writing serves microscopy purposes for the HNA metalens: besides enabling nanofabrication with 100 nm level critical dimension, it provides a universal characterization method for HNA DUV metalenses, addressing the challenges of constructing broadband HNA optical characterization systems in this wavelength range. Furthermore, the HNA AlN metalens for the first time integrates into a confocal photoluminescence system, enabling compact sub-micrometer spectroscopic imaging with DUV excitation and a confocal photoluminescence imaging system using a metalens (NA = 0.7), resolving isolated features down to 300 nm. This work establishes AlN metalenses as a transformative and practical platform for high-resolution DUV applications.