Abstract
We report on the design, fabrication, and analysis of a tunable device combining nanoparticle arrays that support collective surface lattice resonances (SLRs) with liquid crystals (LCs). The optoelectronic tunability of the nematic LC and the dependency of sharp SLRs on the refractive index of the environment are exploited to achieve spectral tunability. This tunability is electrically controlled by switching between planar and homeotropic states in the LC, which allows for a rapid and reversible tuning of the SLR wavelength with a large degree of control. This device also offers the possibility to switch “on” and “off” the presence of a quasi-guided mode in the indium tin oxide electrode. The manipulation of these resonances with an external parameter can be used to expand the functionalities of plasmonic metasurface devices.
Highlights
Plasmonic resonances in metallic nanoparticles, or localized surface plasmon resonances (LSPRs), have created a myriad of possibilities, such as nanolasers,1 extremely sensitive nanosensors for biosensing applications,2,3 and improved photonic devices.4–6 At resonance, free electrons in the metallic nanoparticles coherently oscillate in response to an external oscillating electromagnetic field, leading to efficient light scattering and an increased electric field intensity in close proximity to the particles
We report on the design, fabrication, and analysis of a tunable device combining nanoparticle arrays that support collective surface lattice resonances (SLRs) with liquid crystals (LCs)
We have designed, fabricated, and measured a device consisting of a particle array topped by a nematic LC
Summary
Plasmonic resonances in metallic nanoparticles, or localized surface plasmon resonances (LSPRs), have created a myriad of possibilities, such as nanolasers, extremely sensitive nanosensors for biosensing applications, and improved photonic devices. At resonance, free electrons in the metallic nanoparticles coherently oscillate in response to an external oscillating electromagnetic field, leading to efficient light scattering and an increased electric field intensity in close proximity to the particles. The increased electric field intensity and light scattering lead to increased light absorption by the particles, causing the low Q-factor associated with LSPRs. A way to create resonances with a high Q-factor is to arrange the nanoparticles periodically in an array. Since SLRs in nanoparticle arrays strongly depend on the refractive index of the environment, liquid crystals (LCs) could offer opportunities for the active control of their resonant response. The investigated device consists of an array of aluminum nanoparticles or nanorods fabricated on a transparent indium tin oxide (ITO) electrode with an LC layer on top Both numerical and experimental methods are employed to study the effect on the optical extinction dispersion (defined as 1 À T, where T is the transmittance) when the alignment of the LC is changed. The SLR tunability offered by this device could be employed to realize tunable nanolasers or to improve plasmonic sensors.
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