Metasurfaces having deep sub-wavelength infrared periodicities have been explored in the past for perfect absorbers , active photonic systems, etc. Typically, these metasurfaces exhibit absorption and scattering resonances when the polarization is perpendicular to the stripes, while when the polarization is parallel to the stripes, a broadband high reflectivity is achieved. Metamaterial Longwave Infrared (LWIR) stripe arrays are challenging to fabricate in large (~1” or large) formats, needed for advanced nano-manufacturing, because their sub-wavelength periodicities are too small for standard photolithography in some cases. We employ photolithography to pattern stripe arrays with large periodicities (>7 μm), in order to experimentally verify LWIR diffraction, which has not been generally explored as much as shorter wavelengths, due to challenges in measuring LWIR diffraction in the laboratory. We employ tunable LWIR and Short-wave Infrared SWIR lasers to verify the diffraction from sparser arrays. We pattern metamaterial LWIR arrays using advanced (non-standard) next-generation lithography equipment, and present experimental reflectivity and backwards scattering from these metamaterial LWIR arrays. We simulate, using critical coupling analytical models and the Finite Difference Time Domain (FDTD) numerical algorithm, the reflectivity, scattering, absorption, and transmission of these metamaterial (Aluminum) arrays, and compare to the laser-based measurements. We also measure characteristics of single- and arrayed polymer (polyethylene) fibers, and contrast the results to those of Al stripes in the metasurface. Finally, we compare these measurements to those of a rectangular array of ~ 200 nm Al dots on glass, which showed that forward scattering cuts off for wavelength larger than periodicity, as expected from diffraction theory. Stripe-based metasurface arrays such as these may enable new active metasurfaces in the future, since electrical functionality is easily incorporated in the wire-like high-conductivity stripes extending across the metasurface. Analogous polymer fiber arrays may enable a new generation of smart textiles, if they are integrated with conductive metal fibers or themselves contain conductive additive particles (e.g., metal or carbon nanoparticles). In both cases, being LWIR metamaterials, these metal and polymer stripe and fiber arrays will allow unusual control of thermal functionality – another route, besides electrical, to ‘smart’ active metasurfaces and metamaterials.
In this work, UHMWPE films with different additives were successfully fabricated via a combination of solvent-casting and unixial stretching technique at different draw ratio while fibers of high density polyethylene (HDPE) with silicon and oxide microcomposites were produced by melt-spinning consisting of twin-screw extrusion at various collection rates. The SEM images and DSC data showed the film structure becomes highly oriented along stretching direction and its melting temperature and crystallinity changes considerably by increasing the draw ratio, while the diameters of the fiber samples were reduced by increasing the fiber collecting speed and its crystallinity varies insignificantly with respect to the collecting speed. The optical properties of the polyethylene films and fibers were investigated in the long wave infrared (LWIR) spectral range.
The important nonlinear effect of optical rectification in active metasurfaces,converts high frequency vis/infrared light to direct current. Recently, researchers discovered a reconfigurable optically rectifying junction. We focus on 3 junctions: 1) optical rectification in a simple, lithographically-defined Metal-Insulator-Metal (MIM) diode consisting of a planar Al electrode, a thin Al2O3 barrier layer, and a planar Ag counter-electrode. Applying a voltage grows nm-scale filament from the Al side. 2) nanoplatelet and substrate that demonstrates single-electron tunneling (SET) predict and model low-energy (< fJ) and high speed (>MHz) synaptic operations 3) Experiments conducted to determine whether a ferromagnetic layer in MIM reoriented can change the direct current and the rectified current, when exposed to an incident laser beam. This large tunability enables adaptive ultrafast photon detectors, wireless power transmission, energy harvesting, advanced antennas, computing.
Lightweight, portable solar blankets, constructed from thin film photovoltaics, are of great interest to
hikers, the military, first responders, and third-world countries lacking infrastructure for transporting
heavy, brittle solar cells. These solar blankets, as large as two square meters in area, come close to
satisfying specifications for commercial and military use, but they still have limited absorption due to
insufficient material efficiency, and therefore are large and too heavy in many cases.
Metasurfaces, consisting of monolayers of periodic and semi-random plasmonic particles patterned in
a scalable manner, are explored to enhance scattering into thin photovoltaic films (currently of
significant commercial and military value), in order to enhance absorption and efficiency of solar
blankets. Without nano-enhancement, absorption is limited by the thickness of the thin photovoltaic
active layer in the long-wavelength region. In this study, lithographically patterned, periodic Al
nanostructure arrays demonstrate experimentally a large absorption enhancement, resulting in a
predicted increase in short-circuit current density of at least 35% and as much as 70% for optimized
arrays atop 200-nm amorphous silicon thin films. Optimized arrays extend thin-film absorption to the
near infrared region. This impressive absorption enhancement and predicted increase in short-circuit
current density may significantly increase the efficiency and reduce the weight of solar blankets,
enabling their use for commercial and military applications.
The theory of electromagnetically induced transparency (EIT) in a nonlinear conductive medium, which utilizes the classical approach instead of the traditional quantum optics scheme, has been recently suggested. We present the results of the bichromatic parametric irradiation experiments which validate the EIT effect within the mid-infrared spectrum. The studied materials include a highly dispersive gold (Au) and a low dispersive semiconductor zinc telluride (ZnTe). When the irradiation parameters satisfy the requirements of the EIT theory, the effect was shown to be strongly pronounced in both Au and ZnTe despite the very different optical properties of these conductors. The predictions of the theory regarding the existence of the EIT effect are shown to be in agreement with the experiment.
The effect of electromagnetically induced transparency (EIT) in non-Ohmic conductors, based on the concepts of classical nonlinear optics has been studied theoretically. We report an experimental demonstration of this effect within the mid-IR wavelength range. A low-dispersion semiconductor, i.e. ZnTe, and a highly dispersive gold film were subjected to bichromatic parametric irradiation and when specific phase matching conditions are satisfied, experimental evidence for a strong signature of EIT was found.
Homogeneous negative refractive index materials are introduced as an alternative to normally utilized inhomogeneous metamaterials. The theory of such materials was developed several years ago (A. Kussow and A. Akyurtlu, PRB 78, 205202 (2008)), and the effect is due to the coexistence of the spin-wave mode with the plasmonic mode, and both modes are activated by the electromagnetic field with simultaneous negative permittivity and permeability responses within the narrow frequency band close to the ferromagnetic resonance. To justify this theory, the thin films of ferromagnetic semiconductor, Cr-doped indium oxide, were fabricated, with clearly measured ferromagnetism at high saturation magnetization and a Curie temperature which is much higher than room temperature. The refractive index, within mid-IR, was extracted from combined transmittance and reflectance data and was compared with theoretical prediction. Also, a direct standard beam displacement method validates the effect of negative refraction in this material.
A mechanism based on two-wave mixing to dramatically reduce optical losses in non-ohmic conductors is proposed. The
losses in the probe mode are compensated due to the flow of energy from the support mode. The effect is derived from
the solution of non-linear Maxwell’s equations combined with coherence conditions for two parametrically coupled
waves. We provide a case which shows that this scheme can be realized experimentally in bulk semiconductors, e.g. zinc
telluride (ZnTe), within the mid-IR frequency range.
In this work, we show that natural crystals, or magnetic semiconductor, Cr-doped indium oxide, has a
negative refractive index at ~ 27.8 micron wavelength. The effect was predicted by two of us a few years
ago (A.G. Kussow and A. Akyurtlu, Phys. Rev. B, 78, 205202 (2008)). Our result seriously undermines
wide-spread opinion that only composite artificial metamaterials can demonstrate negative refractive index.
Thin ferromagnetic films of ICO were fabricated by original post-annealing sputtering method. FTIR R and
T measurements were processed to extract refractive index within the range of interest. The extracted from
combined transmittance and reflectance FTIR data negative refractive index band parameters are found to
be close to expected one.