Meta-lens for Vacuum Ultraviolet Light

Description

Vacuum ultraviolet (VUV) light, between wavelength 100 and 200 nm, plays an essential role across science and technology, from molecular spectroscopy to nanolithography and biomedical procedures. Coherent VUV light has been generated by employing high harmonic generation in solids or gases. It can also be produced through free-electron lasers, excimer lasers, and supercontinuum generation in photonic crystal fibers. Realizing nanoscale devices for VUV light generation and control is critical for developing next-generation VUV sources and application systems.Lately, Professors Din-Ping Tsai (currently at CityU, Co-I of this project) and Naomi Halas have demonstrated an all-dielectric nonlinear meta surface for VUV light generation. Their meta surface is composed of an array of zinc oxide nano resonators, which shows a magnetic dipole resonance at 394 nm wavelength. The second harmonic signal at a wavelength of 197 nm is readily generated under 394 nm ultrafast laser pulses excitation. However, the conversion efficiency of their meta surface cannot compete with that of the traditional nonlinear crystal. In this proposal, we design and fabricate a specific dielectric-resonator unit cell with a C3 rotational symmetry for the nonlinear optical process of second-harmonic generation and geometric phase (Pancharatnam-Berry phase) arrangement of this unit cell to simultaneously focus the generated VUV light. We expect our nonlinear meta-lens consists of zinc oxide triangle nano resonators can effectively convert 394 nm light into a focused 197 nm VUV light. The power density of the focusing spot will be enhanced by 2 to 3 orders of magnitude, which is comparable to the commercial nonlinear crystal. Our VUV nonlinear meta-lens is ultra compact and phase-matching free. It can be integrated into various VUV application systems to substantially streamline the design and facilitate more advanced applications. This work provides a useful platform for developing low-loss, multifunctional components for the VUV to increase the accessibility of this important region of the spectrum. We expect the tremendous impact of this project can be commercially available quickly. We trust this project can provide learning opportunities for the students, which will contribute to academic research and industrial developments in the near future. We expect the results of our nonlinear meta-lens can promote the revolution of the next generation VUV photonics, especially the industrial applications in nanolithography, molecular spectroscopy, and biomedical procedures. The advantages of compact size, less mass, efficiency, and energy saving will help the development and replacement of the current bulky and heavy VUV optical devices and systems.