(a) Energy reflection coefficient vs wavelength at critical coupling for film thicknesses of 5 nm (solid curve), 10 nm (dashed curve), and 15 nm (dashed-dotted curve). (b) Quality factor, , for the surface plasmon resonance vs silver film thickness derived from the linewidths shown in (a).
(a) Schematic setup of out-of-phase and in-phase sinusoidal gratings. (b) Unit cell of FDTD simulations. The vertical dashed lines depict the periodic boundaries. Two horizontal dashed lines represent the detection contours. The metal film shown in the center of the unit cell is excited either by a laser pulse generated along a single horizontal line placed a few spatial steps beneath the upper PML region (we refer to this excitation scheme as a single-ended excitation), or by two incident plane waves generated symmetrically on both sides of the film with a fixed phase delay between the incident pulses (referred to as double-ended excitation scheme).
The electromagnetic Wood’s phenomenon in which an incoming wave (entering perpendicular) is diffracted tangent to the grating such that the wave fronts match the grating spacing resulting in anomalies in the reflected and transmitted waves.
Sum of the transmission, , and reflection, , coefficients as a function of the incident wavelength. The solid curve illustrates the single-ended excitation scheme, whereas the dashed and dashed-dotted curves show the double-ended excitation with phase shifts and 0. Panel A corresponds to the out-phase sinusoidal grating with and . Panel B shows data for the in-phase sinusoidal grating with parameters and . The structural parameters for both gratings have been optimized so as to minimize for the double-ended excitation scheme and the long-range mode.
(a) Surface averaged intensity enhancement as a function of the incident wavelength for out-of-phase (solid curve) and in-phase (dashed curve) gratings at the impedance matching conditions for the long-range plasmon mode. (b) Surface averaged intensity enhancement as a function of the film thickness at the impedance matching conditions for long-range plasmon modes for the out-of-phase (squares) and in-phase (circles) sinusoidal grating.
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