Optical meta-devices using metasurfaces have shown preeminent capabilities to control the optical nonlinearity and enhancing the nonlinear efficiency by arrangements of meta-atoms. With the great advantages of relaxed phase-matching requirements and CMOS compatibility for mass production, nonlinear metasurfaces can flexibly manipulate the phase, amplitude and polarization of the nonlinear waves at subwavelength scale. Various nonlinear frequency conversion processes, such as second harmonic generation (SHG), third harmonic generation (THG), have been widely realized to short wavelength such as vacuum ultraviolet (VUV) light and applied in optical communication, imaging, photochemistry and biosensing. The design, fabrication and application of the novel nonlinear optical meta-devices are reported in this talk.
Vacuum ultraviolet (VUV) light is electromagnetic radiation in the wavelength regime between 100nm and 200nm. Due to its high photon energy, VUV light is very important in many advanced applications, such as photochemistry, nanolithography, and novel spectroscopy. While several methods to generate coherent VUV light have been developed, a multifunctional nanophotonic device for efficient VUV light generation and control still remains an outstanding challenge. In this work, we demonstrate an all-dielectric metasurface device (metadevice) which can be used for nonlinearly generating coherent VUV light. Metasurfaces are artificial nanostructures with resonance properties that can be designed by carefully tailoring their geometric parameters. The metadevice demonstrated in this work consists of an array ZnO nano-resonators. To fabricate the metadevice, a 150-nm multicrystalline ZnO was nanopatterned using a focus ion beam system. In the linear transmission measurement, the metadevice shows a resonance dip at around 400nm. This resonance was found to be associated to a magnetic dipole resonance of the nano-resonators. When a visible femtosecond laser beam (wavelength: 394nm) as an excitation source was loosely focused on the metadevice, VUV light originating from second harmonic generation of the metadevice was produced. The dependence of the VUV signal on the excitation power as well as on the incident angle were carefully measured and analyzed. Furthermore, manipulation of the output VUV wavefront was realized by carefully controlling the nano-resonator arrangement. This work paves a novel route toward high-efficiency multifunctional nanophotonic devices for VUV applications [Nano Lett. 18, 5738 (2018)].
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