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Toward broadband, dynamic structuring of a complex plasmonic field

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Science Advances  01 Jun 2018:
Vol. 4, no. 6, eaao0533
DOI: 10.1126/sciadv.aao0533
  • Fig. 1 Digitally reconfigurable structuring of SPPs.

    (A) Schematic diagram of the experiment. A 4-f system consisting of an achromatic doublet lens (f = 500 mm) and an objective lens (20×; numerical aperture, 0.45) was used to project the phase distribution (loaded onto the SLM) to the ring structure milled in a gold thin film. The phase distribution of the SPPs generated at the ring coupler is thus determined by incident light. As a result, the desired SPP field formed by the converging SPPs is found around the geometric center of the ring. A near-field scanning optical microscope (NSOM) working in collection mode was used to measure the SPP fields on the gold surface. (B) A 2D Fourier relationship can be established between the complex amplitude U(ξ, ζ) along a ring of a converging surface wave and the out-of-plane component of the SPP field Ez(x, y) in the vicinity of the geometrical focus. The phase distribution of the initial launching condition at the ring coupler is obtained through an iterative algorithm. (C) Scanning electron microscopy (SEM) micrograph of the ring-groove nanostructure. The diameter of the ring is 40 μm, while the width of the groove is 240 nm. Scale bar, 5 μm.

  • Fig. 2 Structured SPP fields with desired intensity distributions.

    (A) Ring-shaped intensity pattern. (B and C) Elliptically shaped intensity patterns with different eccentricities [0.8 in (B) and 0.9 in (C)] and orientations. (D) Petal-shaped intensity pattern. (A1 to D1) Top row: Target intensity distributions. (A2 to D2) Two-dimensional field distributions (only intensity profiles are shown here) found by our algorithm that approximate the targets. (A3 to D3) Full-wave simulation results of resultant SPP waves excited by the corresponding initial ring phase distributions (obtained by the algorithm). (A4 to D4) Intensity distributions measured by the NSOM. Scale bar, 5 μm.

  • Fig. 3 In-plane phase controlling.

    (A) Ellipse intensity target intensity. There are two degenerate solutions that obey the in-plane wave equation found by our algorithm that approximate the targets. (B and F) The intensities of these two solutions are the same. (C and G) The phase gradients of the solutions are reversed from counterclockwise to clockwise. (D and H) The zoomed-in areas of (C) and (G) (close-ups of the areas indicated by the yellow dashed squares) indicate that the propagation directions of the SPP waves are reversed. Here, the phases of the low-intensity areas are set to zero to highlight the phase gradient. (E and I) Poynting vectors with intensity distributions in the background [the same areas as (D) and (H)] show that the energy flows are reversed. Scale bar, 5 μm.

  • Fig. 4 Broadband structuring of SPP fields.

    (A to C) Rows: Different SPP field targets excited by incident beams with different wavelengths (532, 633, and 780 nm). (A1 to C1) Target intensity distributions. (A2 to C2) Intensity distributions of the 2D field found by our algorithm that approximate the targets. (A3 to D3) Full-wave simulation results of resultant SPP waves excited by the corresponding initial ring phase distributions.

  • Fig. 5 Discussion of in-plane SPP spiral phase field structuring.

    (A) Spiral phase distribution of the target PV with a topological charge value of 40. (B) Target intensity distribution of the PV field is set to the same size as the phase distribution. The radius R was set to be the same as the radius of the eigenmode PV’s main intensity profile. (C and D) Intensity distribution and phase distribution found by our algorithm. The images show that this PV field can be resolved. (E and F) Spiral phase distribution and intensity distribution of the target PV field with a double-size radius 2R of (A) and (B). (G and H) The results obtained using our algorithm show that this target PV field could not be generated on a metal surface with a main intensity profile that was mismatched in size. The energy still flows to the ring position with a radius of R generating a PV field whose charge is equal to 40. But the amplitude in (F) is much smaller than in (D). Scale bar, 5 μm.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/6/eaao0533/DC1

    section S1. In-plane FT for converging SPP waves

    section S2. Algorithm for obtaining the initial launching distribution of the SPP fields

    section S3. Compensating spiral phase carried by the circularly polarized beam

    section S4. Discussion on the spatial resolution of the generated SPP field

    section S5. Experimental setup

    section S6. Experimental demonstration of the phase control

    section S7. Additional results for dynamically structuring SPP fields

    fig. S1. Derivation of the in-plane FT of surface waves.

    fig. S2. Algorithm process flow to obtain the initial launching distribution of the SPP fields.

    fig. S3. Schematic diagram of the spiral phase compensation by an inverse spiral phase distribution.

    fig. S4. Single focused spot of plasmonic field.

    fig. S5. Two equally bright coherent spots separated by one full width at half maximum with the phase difference between the two spots as 0, π, and 0.5π.

    fig. S6. Schematic diagram of the experimental setup.

    fig. S7. Experimental demonstration of dynamic switching of the phase gradient.

    fig. S8. Results for dynamically structuring SPP fields.

    movie S1. Clockwise energy flow for the elliptical plasmonic field.

    movie S2. Counterclockwise energy flow for the elliptical plasmonic field.

    References (4044)

  • Supplementary Materials

    This PDF file includes:

    • section S1. In-plane FT for converging SPP waves
    • section S2. Algorithm for obtaining the initial launching distribution of the SPP fields
    • section S3. Compensating spiral phase carried by the circularly polarized beam
    • section S4. Discussion on the spatial resolution of the generated SPP field
    • section S5. Experimental setup
    • section S6. Experimental demonstration of the phase control
    • section S7. Additional results for dynamically structuring SPP fields
    • fig. S1. Derivation of the in-plane FT of surface waves.
    • fig. S2. Algorithm process flow to obtain the initial launching distribution of the SPP fields.
    • fig. S3. Schematic diagram of the spiral phase compensation by an inverse spiral phase distribution.
    • fig. S4. Single focused spot of plasmonic field.
    • fig. S5. Two equally bright coherent spots separated by one full width at half maximum with the phase difference between the two spots as 0, π, and 0.5π.
    • fig. S6. Schematic diagram of the experimental setup.
    • fig. S7. Experimental demonstration of dynamic switching of the phase gradient.
    • fig. S8. Results for dynamically structuring SPP fields.
    • References (40–44)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Clockwise energy flow for the elliptical plasmonic field.
    • movie S2 (.mp4 format). Counterclockwise energy flow for the elliptical plasmonic field.

    Files in this Data Supplement:

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