All-optical control of surface plasmons by second-harmonic generation

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All-optical control of surface plasmons by second-harmonic generation

Sergio G. Rodrigo

Phys. Rev. B 98, 041407(R) – Published 31 July 2018

Abstract

All-optical control of surface plasmon polaritons (SPPs) is theoretically demonstrated in arrays of metallic slits. It is shown how the mixing of electromagnetic fields scattered by the slits from a weak beam at $λ$ wavelength, with second-harmonic fields generated by a high-intensity $2 λ$ beam, creates a destructive interference of surface plasmons in one of the two possible directions of emission from the slits, while these are enhanced along the opposite direction. Our method enables spectrally broadband excitation and thus unidirectional launching of SPP pulses as short as $\sim 20$ fs, all-optically controlled. Based on these findings, an ultranarrow bandwidth surface plasmon frequency comb is designed.

Received 16 January 2018
Revised 6 July 2018

DOI:https://doi.org/10.1103/PhysRevB.98.041407

Physics Subject Headings (PhySH)

Nanophotonics Surface plasmon polariton

Finite-difference time-domain method Optical second-harmonic generation

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Sergio G. Rodrigo^*

Instituto de Ciencia de Materiales de Aragón and Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza, E-50009 Zaragoza, Spain and Centro Universitario de la Defensa, Carretera de Huesca s/n, E-50090 Zaragoza, Spain

^*sergut@unizar.es

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Issue

Vol. 98, Iss. 4 — 15 July 2018

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Images

Figure 1
All-optical control of SPPs by SHG. The simultaneously occurring suppression and enhancement of SPP currents in opposite directions is a consequence of the different symmetry of SPPs generated by a signal beam at $λ$ and the SH field generated by a $2 λ$ control beam.
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Figure 2
(a) Linear transmittance (normalized to the amount of light directly illuminating the area of the apertures) through an infinite array of slits (thick line) and different finite systems, for plane-wave illumination. In linear and nonlinear calculations the system is illuminated at normal incidence, and the electric field polarized along the $x$ axis. The geometrical parameters are $p = 300$ nm, $w = 100$ nm, and $h = 300$ nm. The system is surrounded by air. (b) Top: Real part of the magnetic field component $H_{y}$ scattered from the signal beam at $λ = 600$ nm. Bottom: $H_{y}$ at SH wavelength generated by a $2 λ$ control beam. The white lines show $H_{y}$ at $z = 0$ . These calculations are obtained with continuous-wave Gaussian beam illumination. (c) Coherent control of SPP directionality by the relative phase $δ$ between signal and control beams at $λ = 600$ nm. The power ratio to the right (black) and to the left (red) are calculated with FDTD for continuous waves (solid symbols) and for 100-fs pulses (open symbols). The corresponding trends are fitted to sinusoidal functions (solid and dashed lines). (d) Snapshots of the electric field amplitude for the values of $δ$ labeled with integer numbers and capital letters in (c), and both beams are switched on. Map scale: White (maximum) and black (minimum). (See also the video of 100-fs-laser unidirectional launching SPPs given in the SM).
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Figure 3
Demonstration of dynamical control of SPPs at the signal wavelength $λ = 600$ nm. During a single FDTD simulation spanning $T_{simulation} \sim 10$ ps, the relative phase between the signal and control beams is periodically changed, producing a train of 1-ps SPP pulses to the left, as shown in (a) with a blue line (EM fields from a point located 9 $μ m$ to the left from the central slit). These values correspond to an enhancement-suppression sequence in $P_{L}$ , in agreement with Fig. 2. (b) Demonstration of a SPP frequency comb. The solid blue line shows the spectral response from the EM fields in (a). The frequency comb spacing $f_{R} = 1 / T = 0.5$ THz corresponds to a pulse period $T = 2$ ps. The green dashed line represents the spectral response of the 10-ps signal pulse (control beam switched off) and the gray solid line the corresponding for a single 1-ps pulse. The inset shows the same as that in the main figure but for a wider frequency window (log scale). The spectral response of the square function shown in (a) (red line) is included in the inset.
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