Deep- and vacuum-ultraviolet metaphotonic light sources

Recent demonstrations of deep- and vacuum-ultraviolet (DUV and VUV) light emission from artificially engineered meta-atoms through nonlinear harmonic signal generation processes have opened up new avenues for fundamental engineering approaches and modern applications. While many different phenomena based on optical metasurfaces have been revealed in linear optics, several studies have reported the observation of various nonlinear optical phenomena in such nanosystems, like, for example, second and third harmonic generation (SHG and THG), multiphoton luminescence, higher harmonic generation, and four-wave mixing. Plasmonic and all-dielectric flatland metasurfaces enable successful manipulation of light-matter interactions on ultradense platforms and provide substantial enhancement of driving fields, which make these architectures promising and attractive to efficiently radiate intense and coherent second and third harmonic radiations. In this focused Review, we highlight and discuss the recent state-of-the-art methods that have been developed and proposed for the generation of nonlinear harmonic signal and high-energy DUV and VUV lights. This contribution not only summarizes the strategies that have been exploited for augmenting the intensity of nonlinear UV signal, but also introduces the novel mechanisms to strongly optimize the conversion efficiency of this principle. We envisage that this understanding allows to compare the performance of versatile nonlinear DUV and VUV metasources and paves the way of designing much more efficient light emitting tools such as lasers, super-resolution imaging nanosystems, and nanolithography apertures.