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Efficient ultrafast all-optical modulation in a nonlinear crystalline gallium phosphide nanodisk at the anapole excitation

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Science Advances  21 Aug 2020:
Vol. 6, no. 34, eabb3123
DOI: 10.1126/sciadv.abb3123
  • Fig. 1 Design and linear simulations of GaP nanoantennas.

    (A) Scanning electron microscopy image of the fabricated sample. The inset shows a magnified view of a nanodisk of 600-nm diameter. Scale bars, 1 μm (main image) and 200 nm (inset). (B) Simulated scattering (Scatt.) cross section for disks of 560-, 600-, and 640-nm diameter. AE denotes the anapole excitation (encircled minima). In the bottom of the graph, the pump and probe spectra are displayed in arbitrary intensity units. (C) Calculated electric energy for the D = 600-nm nanodisk, computed as WE ∝ ∭∣E2dV, with V denoting the volume of the nanoantenna. The simulated electric field distributions corresponding to the most prominent peaks are included at selected disk heights presenting maximum field accumulation. From lowest to highest wavelength, corresponding height values as measured from the substrate are 25, 70, 20, and 5 nm. a.u., arbitrary units.

  • Fig. 2 Pump/probe spectroscopy results of single GaP nanodisks.

    (A to C) Differential reflectivity spectra of individual nanoantennas of diameters D = 560, 600, and 640 nm, registered by pumping the sample at P = 10 pJ/μm2, with a 5:1 pump-probe fluence ratio.

  • Fig. 3 Experimental and simulated nonlinear responses.

    (A) Experimental and (B) simulated differential reflectivity response at t = 0 fs and P = 10 pJ/μm2 for D = 560 nm (blue), 600 nm (red), and 640 nm (green). The inset of (A) shows the registered response from a commercial double-sided polished 350-μm-thick GaP (100) wafer measured under the same experimental conditions. The inset of (B) exhibits the simulated response of the D = 600-nm antenna when considering the OKE contribution only (n2 = 2 × 10−18 m2/W and β = 0 cm/GW), the TPA contribution only (n2 = 0 m2/W and β = 3 cm/GW), their direct sum, and the full simulation (sim.) (n2 = 2 × 10−18 m2/W and β = 3 cm/GW). The latter matches the red curve in the main graph.

  • Fig. 4 Modulation performance at different pump powers.

    (A) Pump peak energy density dependence of |ΔR/R| at selected probe wavelengths for nanoantennas with D = 560 nm (λ = 785 nm), D = 600 nm (λ = 815 nm), and D = 640 nm (λ = 845 nm). (B) Corresponding temporal trace results at specific pump peak energy densities detailed in the graph for the two most efficient disks. Solid lines correspond to exponential fits to the experimental data. IRF, instrument response function.

Supplementary Materials

  • Supplementary Materials

    Efficient ultrafast all-optical modulation in a nonlinear crystalline gallium phosphide nanodisk at the anapole excitation

    Gustavo Grinblat, Haizhong Zhang, Michael P. Nielsen, Leonid Krivitsky, Rodrigo Berté, Yi Li, Benjamin Tilmann, Emiliano Cortés, Rupert F. Oulton, Arseniy I. Kuznetsov, Stefan A. Maier

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