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Surface plasmon polaritons (SPPs) at metal-dielectric interfaces provide strong out-of-plane confinement enabling nano-scale sensing and imaging, yet diffraction causes spatial delocalization. Conventional strategies to combat diffraction through spatial structuring are inapplicable to dimensionally restricted SPPs, except for nonlocalized cosine plasmons and Airy plasmons that follow curved trajectories. Here we demonstrate space-time SPPs (ST-SPPs), ultrashort (16-fs) diffraction-free SPPs that propagate rectilinearly via precise sculpting of their spatiotemporal spectra. By synthesizing a spatiotemporally structured field in free space and coupling the field to an axially invariant ST-SPP at a metal-dielectric surface, we control the ST-SPP group velocity and propagation characteristics. Time-resolved two-photon fluorescence microscopy reconstructs the surface-bound field in space and time, verifying the predicted spatiotemporal wavefront and diffraction-free propagation. Our work opens new avenues for combining spatiotemporally structured light with the field-localization associated with nanophotonics, and may thus enable novel applications in surface-enhanced sensing and nonlinear optical interactions.
The authors report the observation of diffraction-free space-time surface plasmon polaritons propagating along straight paths at metal-dielectric interfaces. This enhances the control of wavepacket propagation for nanophotonics applications.
Details
; Kikuchi, Hibiki 2 ; Yessenov, Murat 3
; Schepler, Kenneth L. 4
; Abouraddy, Ayman F. 4
; Kubo, Atsushi 5
1 Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba-shi, Japan (ROR: https://ror.org/02956yf07) (GRID: grid.20515.33) (ISNI: 0000 0001 2369 4728); Institute of Industrial Science, The University of Tokyo, Meguro-Ku, Japan (ROR: https://ror.org/057zh3y96) (GRID: grid.26999.3d) (ISNI: 0000 0001 2169 1048)
2 Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba-shi, Japan (ROR: https://ror.org/02956yf07) (GRID: grid.20515.33) (ISNI: 0000 0001 2369 4728)
3 Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA (ROR: https://ror.org/03vek6s52) (GRID: grid.38142.3c) (ISNI: 0000 0004 1936 754X); CREOL, The College of Optics & Photonics, University of Central Florida, Orlando, FL, USA (ROR: https://ror.org/036nfer12) (GRID: grid.170430.1) (ISNI: 0000 0001 2159 2859)
4 CREOL, The College of Optics & Photonics, University of Central Florida, Orlando, FL, USA (ROR: https://ror.org/036nfer12) (GRID: grid.170430.1) (ISNI: 0000 0001 2159 2859)
5 Department of Physics, Institute of Pure and Applied Sciences, University of Tsukuba, Tsukuba-shi, Japan (ROR: https://ror.org/02956yf07) (GRID: grid.20515.33) (ISNI: 0000 0001 2369 4728)