Nano Lett. 18, 5738–5743 (2018)
Ultraviolet light with wavelengths in the 100–200 nm range (known as the vacuum ultraviolet; VUV) has applications in nanofabrication, photochemistry and spectroscopy, to name just a few areas. At present, VUV light is typically generated by nonlinear processes in gases, which is not the most convenient or easily integrated approach. Now, Michael Semmlinger and colleagues in the US and Taiwan have demonstrated an all-dielectric metasurface that generates 197-nm light by resonantly enhanced second-harmonic generation. The structure is a periodic array of dielectric resonators fabricated by sputtering a 150-nm-thick layer of ZnO and patterning it by focused-ion-beam lithography. The resonator array was designed with a magnetic dipole resonance at 394-nm wavelength and provides an average effective nonlinear coefficient of 0.96 pm V–1 for pump powers below 0.2 mW that declines to 0.66 pm V–1 for higher pump powers. This is several times higher than an unstructured ZnO thin film (~0.20 pm V–1) and double that of potassium fluoroboratoberyllate (KBBF). At present, the substrate is glass, which absorbs VUV; the effective nonlinear coefficient may actually be higher if a different substrate material is used.