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. 2022 Apr 22;8(16):eabn5644.
doi: 10.1126/sciadv.abn5644. Epub 2022 Apr 20.

Vacuum ultraviolet nonlinear metalens

Ming Lun Tseng  1   2 , Michael Semmlinger  3   4   5 , Ming Zhang  4   5   6 , Catherine Arndt  3   4   5 , Tzu-Ting Huang  2 , Jian Yang  4   5   6 , Hsin Yu Kuo  7 , Vin-Cent Su  8 , Mu Ku Chen  9 , Cheng Hung Chu  2 , Benjamin Cerjan  3   4 , Din Ping Tsai  2   7   9 , Peter Nordlander  3   4   6 , Naomi J Halas  3   4   6   10
Affiliations

Vacuum ultraviolet nonlinear metalens

Ming Lun Tseng et al. Sci Adv. .

Abstract

Vacuum ultraviolet (VUV) light plays an essential role across science and technology, from molecular spectroscopy to nanolithography and biomedical procedures. Realizing nanoscale devices for VUV light generation and control is critical for next-generation VUV sources and systems, but the scarcity of low-loss VUV materials creates a substantial challenge. We demonstrate a metalens that both generates-by second-harmonic generation-and simultaneously focuses the generated VUV light. The metalens consists of 150-nm-thick zinc oxide (ZnO) nanoresonators that convert 394 nm (~3.15 eV) light into focused 197-nm (~6.29 eV) radiation, producing a spot 1.7 μm in diameter with a 21-fold power density enhancement as compared to the wavefront at the metalens surface. The reported metalens is ultracompact and phase-matching free, allowing substantial streamlining of VUV system design and facilitating more advanced applications. This work provides a useful platform for developing low-loss VUV components and increasing the accessibility of the VUV regime.

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Figures

Fig. 1.
Fig. 1.. VUV nonlinear metalens design.
(A) Idealized schematic. (B) Geometric parameters of each meta-atom: edge length (L), 205 nm; thickness (T), 150 nm. The meta-atoms are arranged in a hexagonal lattice with a lattice constant of 270 nm. (C) Theoretical calculation of resonance amplitudes for electric dipole (E-dipole) and magnetic dipole (M-dipole). Inset: Simulation of the electric field enhancement within the meta-atom. (D) Simulation of the SHG signal versus the excitation wavelength. (E) Simulation of the phase modulation and nonlinear output intensity versus rotation angle at the SHG wavelength (197 nm). Blue curve and axis: Simulated nonlinear phase modulation. Red curve and axis: Simulated amplitude of SHG wave. a.u., arbitrary units.
Fig. 2.
Fig. 2.. Fabrication of the VUV nonlinear metalens.
(A) Layout of the nonlinear metalens. A color code is imposed on the meta-atoms with different rotation angles to illustrate the phase profile encoded on the metasurface. An enlarged image of the phase profile is shown as the insert. (B) Optical microscopic image of the metalens. (C) SEM images of the ZnO meta-atoms at the highlighted boxes in the optical image (top right). (D) Linear transmission spectrum of the metalens. Top: Experimental data. Bottom: Simulation data. (E) Nonlinear spectral measurement. SHG spectrum of the metalens. Wavelength increment is 0.2 nm.
Fig. 3.
Fig. 3.. Focusing measurements of the VUV nonlinear metalens.
(A) Experimental setup. SF, spatial filter; λ/4, quarter-wave plate; LP, linear polarizer; O, objective; BPFs, bandpass filters. (B) Focusing profile. (C) Image of the focusing spot (z = 142 μm). (D) Image at metalens surface (z = 0). Comparison between the measured and simulated intensity cross sections of the focusing spot along the (E) x axis and (F) z axis, respectively.
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