This paper describes a symmetry-breaking plasmonic lattice structure that can support narrow resonances as optical feedback for nanolasing. A scalable technique is developed to fabricate nanocrescent arrays with low-structural symmetry unit cells to achieve in-plane quadrupolar lattice plasmon modes. These lattice plasmons with extremely narrow linewidths preserve nonzero net dipole moments under normal excitation. Ultrafast band-edge lasing can be switched on and off by changing the polarization of the incident pump light. The quadrupolar lattice plasmon lasing process is simulated with a semi-quantum model and the sharp tips on the nanocrescents accelerate the lasing buildup process and enhance stimulated emission.
We report an ultrafast optical switching device constructed by stacking two layers of gold nanowires into a perpendicularly crossed network, which works at a speed faster than 280 fs with an on/off modulation depth of about 22.4%. The two stacks play different roles in enhancing consistently the optical switching performance due to their different dependence on the polarization of optical electric fields. The cross-plasmon resonance based on the interaction between the perpendicularly stacked gold nanowires and its Fano-coupling with Rayleigh anomaly is the dominant mechanism for such a high-contrast optical switching device.
induces electron-electron, electronphonon, and phonon-phonon scattering processes. [19] Electron scattering process takes place in the very early stage after the optical excitation and evolves in a time scale shorter than 100 fs; however, the interaction between electrons and phonons due to the energy exchange between the excited electrons and lattices [19,20] gen erally prolongs the decay dynamics of SPP or LSPR to picoseconds. The electron dominated dynamics laid the basis for the SPP or LSPRbased ultrafast alloptical switching, [21][22][23] ultrafast beam steering, [24] optical modulation, [25,26] optical logic devices, [27] and bandtunable metamaterial with lowpower excitation. [28,29] In this work, we investigate multipolar surface plasmon polaritons excited in periodically arranged gold hemispherical nanoshells on an indiumtinoxidecoated silica substrate. Making use of the efficient optical response of the SPPinduced resonance modes, we explore applications of the narrowband optical filtering and ultrafast optical switching effects. Figure 1a shows the design of the array of plasmonic hemi sphere nanoshells (HSNSs). In the fabrication, interference lithography was employed to produce a 2D grating of photore sist (PR) with a period of 400 nm and a modulation depth of about 140 nm, where an He-Cd laser at 325 nm was used as the UV light source and the positive PR S1805 was used as the recording medium. A glass plate deposited with 200 nm thick indium tin oxide (ITO) was used as the substrate. The homo geneous structures take up an effective area as large as 10 mm in diameter. Then, gold was deposited onto the top surface of the PR grating with a thickness of about 50 nm. Since the photoresist was developed to the bottom during interference lithography, the hemisphere nanoshells are connected by the continuous gold film on ITO. The plasmonic HSNSs con sisting of PRcore/goldnanoshell array are shown by the top and bottomview scanning electron microscope (SEM) images in Figure 1b,c, respectively. The inset in the righttop corner of Figure 1b shows a close look at an HSNS, which has a diam eter of about 260 nm. The bottomview SEM image in Figure 1c has been measured on a peeloff piece of the HSNSs. Figure 1d shows the reflective optical extinction spectra for s (perpen dicular to the incident plane) and p (parallel to the incident plane) polarizations, which have been measured in the reflec tion space above the gold deposition (+) and below the substrate (−). The reflective optical extinction spectra were calculated This study reports ultrafast multipolar plasmons in a large-area periodic array of hemisphere gold nanoshells. A dipolar plasmon is observed as a resonance mode at longer wavelengths, where the free electrons are driven to oscillate through the nanoshells and the corresponding resonance spectrum is determined by the size of the hemisphere nanoshells. However, a hexapolar plasmon is observed to resonate at shorter wavelengths, where the free electrons are driven to oscillate in the inner shell and in t...
Access to surface plasmon polaritons (SPPs) with directional control excited by electrical means is important for applications in (on-chip) nano-optoelectronic devices and to circumvent limitations inherent to approaches where SPPs are excited by optical means (e.g., diffraction limit). This paper describes directional excitation of surface plasmon polaritons propagating along a plasmonic strip waveguide integrated with an aperiodic groove array electrically driven by an Al–Al2O3–Au tunnel junction. The aperiodic groove array consists of six grooves and is optimized to specifically reflect the SPPs by 180° in the desired direction (+x or −x) along the plasmonic strip waveguide. We used constrained nonlinear optimization of the groove array based on the sequential quadratic programming algorithms coupled with finite-difference time-domain (FDTD) simulations to achieve the optimal structures. Leakage radiation microscopy (Fourier and real plane imaging) shows that the propagation direction of selectively only one SPP mode (propagating along the metal–substrate interface) is controlled. In our experiments, we achieved a directionality (i.e., +x/−x ratio) of close to 8, and all of our experimental findings are supported by detailed theoretical simulations.
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