Low-loss metasurface optics down to the deep ultraviolet region

Nanopillars that manipulate UV light An array of hafnium oxide nanopillars on a fused silica substrate efficiently manipulates a broad range of ultraviolet light wavelengths, with potential applications in photolithography, imaging, spectroscopy, and quantum information processing. A resist-based Damascene process was developed by a team led by Cheng Zhang, Ting Xu and Henri J. Lezec in China and the USA. They used lithography to design spaces into a resist template that were then filled with hafnium oxide. The resist was removed with solvent to leave high-aspect-ratio hafnium oxide nanopillars. The pillar height, diameter and orientation, as well as the spacing between the pillars, control how UV light propagates through the thin 'metasurface'. Metasurfaces were used to focus UV light like a lens; transform incident UV light into a propagating, curving output beam; and generate holograms from three UV light wavelengths. Shrinking conventional optical systems to chip-scale dimensions will benefit custom applications in imaging, displaying, sensing, spectroscopy, and metrology. Towards this goal, metasurfaces-planar arrays of subwavelength electromagnetic structures that collectively mimic the functionality of thicker conventional optical elements-have been exploited at frequencies ranging from the microwave range up to the visible range. Here, we demonstrate high-performance metasurface optical components that operate at ultraviolet wavelengths, including wavelengths down to the record-short deep ultraviolet range, and perform representative wavefront shaping functions, namely, high-numerical-aperture lensing, accelerating beam generation, and hologram projection. The constituent nanostructured elements of the metasurfaces are formed of hafnium oxide-a loss-less, high-refractive-index dielectric material deposited using low-temperature atomic layer deposition and patterned using high-aspect-ratio Damascene lithography. This study opens the way towards low-form factor, multifunctional ultraviolet nanophotonic platforms based on flat optical components, enabling diverse applications including lithography, imaging, spectroscopy, and quantum information processing.