Extraordinarily Transparent Metaldielectrics for Infrared and Terahertz Applications

Abstract

Metamaterials are extremely important in advanced technologies, but usually, they rely on the resonant behavior of their constituent blocks. This strongly limits the application of metamaterials to particular frequency band ranges. However, metamaterials with broadband behaviors are highly desirable and are essential for many applications. Herein, recently discovered metamaterials that are composed of densely packed metallic nanoparticles but behave as effective dielectrics are explored. Such metamaterials are extremely transparent for all wavelengths within or exceeding the near infrared and their performance is constant across an ultra‐broadband range of frequencies, which is vital to many devices that operate across the same frequency range. The ability to tune the refractive index of these metamaterials to unnaturally high values while maintaining transparency opens new avenues, such as creating flat, thin metalenses in the terahertz region where only bulk lenses are currently available. To highlight those features, several new possible infrared and terahertz applications of these metamaterials which push the boundary of existing technology in THz photonics are shown.

Wet Chemical Engineering of Nanostructured GRIN Lenses

“…[ 1 ] In this way, we solve for the effective index of compact metallic structures with high accuracy, using finite‐differences or finite‐elements to discretize our system. Interestingly, when the particles are much smaller than the wavelength, even in the case of small gaps (when multipolar orders are expected), the following simple Maxwell‐Garnett approximation gives accurate results: [ 2 ] $$$$\begin{equation} \epsilon _{eff} = \epsilon _{m}\frac{2\rho (\epsilon _i-\epsilon _m) + \epsilon _i + 2\epsilon _m}{2\epsilon _m+\epsilon _i-\rho (\epsilon _i-\epsilon _m)} \end{equation}$$$$where, ϵ eff is the effective dielectric constant of the medium, ϵ i of the inclusions, and ϵ m of the matrix; and ρ is the volume fraction of the inclusions. The above expression considers spherical inclusions.…”

“…However, it can be shown that we can obtain analytical expressions for the effective refractive index when metal nanoparticles have simple shapes such as cubes, cylinders, etc. [ 2 ]…”

Nanofocusing in Critically Coupled Nanogap Waveguide Resonators

“…Nanofocusing has emerged as a powerful tool in the field of nanophotonics, offering unprecedented control and manipulation of light at the nanoscale. − The technique enables the concentration of optical energy to dimensions well below the diffraction limit of light holding great promise for a wide range of applications, including data communications, high-resolution imaging, optical sensing, and nanoscale spectroscopy . Nanofocusing is best recognized in nanophotonic waveguides that exhibit adiabatic tapering using either sharp metallic tips ,, or narrow gaps in metal − or dielectric , structures. Here, we explore nanofocusing in resonant optical antennas.…”

Plasmonic Polarization Rotation in SERS Spectroscopy

“…In previous works, metallic nanoparticles and the nanogaps in particle clusters have been utilized to enhance the weak ROA signal from chiral molecules absorbed on the surface of those particles or in the gaps, − where electric field hot spots exist. , The majority of researchers have focused on studying the polarization difference in the intensity of Raman scattering from chiral molecules on isotropic surfaces, with the common understanding being that the ROA signal arises from the intrinsic properties of the Raman tensor of the analyte (the chirality of molecules). However, it is also crucial to consider the orientation of the molecule with respect to the metallic nanoparticle surfaces and the chiral properties of the nanoparticles, as these can also influence the Raman signal.…”