Metasurfaces manipulate light through engineering the amplitude, phase and polarization across arrays of meta-atom antenna resonators. Adding tunability and active functionality to metasurface components would boost their potential and unlock a vast array of new application possibilities such as dynamic beam steering, LIDAR, tunable metalenses, reconfigurable meta-holograms and many more. We present here high-index reconfigurable meta-atoms, resonators and metasurfaces that can dynamically and continuously tune their frequency, amplitude and phase, across the infrared spectral ranges. We utilize narrow linewidth resonances along with peak performance of tunable mechanisms for efficient and practical reconfigurable devices.
Metasurfaces allow unprecedented control of light through engineering the amplitude, phase and polarization across arrays of meta-atom resonators. Adding dynamic tunability to metasurface components would boost their potential and unlock a vast array of new application possibilities such as dynamic beam steering, LIDAR, tunable metalenses and reconfigurable meta-holograms, to name a few. We present here high-index reconfigurable metaatoms, resonators and metasurfaces that can dynamically and continuously tune their frequency, amplitude and phase, across the near to mid-infrared spectral ranges. We highlight the importance of narrow linewidth resonances along with peak performance of tunable mechanisms for efficient and practical reconfigurable devices.
Hybrid materials allow the engineering of new material properties by creative uses of proximity effects. When two dissimilar materials are in close physical proximity the properties of each one may be radically modified or occasionally a completely new material emerges. In the area of magnetism, controlling the magnetic properties of ferromagnetic thin films without magnetic fields is an on- going challenge with multiple technological implications for low- energy consumption memory and logic devices. Interesting possibilities include ferromagnets in proximity to dissimilar materials such as antiferromagnets or oxides that undergo metal-insulator transitions. The proximity of ferromagnets to antiferromagnets has given rise to the extensively studied Exchange Bias[1]. Our recent investigations in this field have addressed crucial issues regarding the importance of the antiferromagnetic [2-3] and ferromagnetic [4] bulk for the Exchange Bias and the unusual short time dynamics [5]. In a series of recent studies, we have investigated the magnetic properties of different hybrids of ferromagnets (Ni, Co and Fe) and oxides, which undergo metal-insulator and structural phase transitions. Both the static as well as dynamical properties of the ferromagnets are drastically affected. Static properties such as the coercivity, anisotropy and magnetization [6-8] and dynamical properties such as the microwave response are clearly modified by the proximity effect and give raise to interesting perhaps useful properties.
Work supported by US-AFOSR and US-DOE
We report the analogies between the electrical properties at low temperatures of oxygen deficient cuprates and manganites thin films under illumination by UV or visible light. For the cuprates, a decrease of the oxygen content decreases the critical temperature of the transition from the normal to the superconducting state while for the manganites it decreases the transition temperature at which the insulator-metal transition occurs. For full oxygenated cuprates and manganites thin films there is no effect of the illumination on the electrical properties of the films. For small oxygen deficient cuprates (in the normal state) and manganites thin films, light increases substantially the conductivity leading to a persistent photoinduced conductivity (PPC) and the effect of persistent photoconductivity increases with oxygen deficiency. For high oxygen deficiency, the cuprates and the manganites are insulating. In that case, a transient photoconductivity is observed in the cuprates and manganites. Moreover, a photoinduced insulator- metal (I-M) transition appears in these insulating thin films.
We have performed extensive model calculations in order to understand the effect that roughness
has on the X-ray diffraction from multilayers. We have developed models to calculate the low and
the high angle X-ray diffraction spectra, including kinematic and dynamical simulations. These
model calculations were used to understand a variety of systems including crystalline/crystalline,
crystalline/amorphous and amorphous/amorphous multilayers. These model calculations were
compared with the diffraction spectra of multilayered systems prepared using sputtering and
Molecular Beam Epitaxy (MBE) techniques.
Using the experience acquired from these model calculations we have recently developed a
comprehensive nonlinear optimization program to refine the structure of multilayers from X-ray
diffraction spectra. Kinematic formulation is used to refine the high angle data and dynamical
(Fresnel) formalism was used to fit the low angle spectra. A comparison of the results obtained
from the structural refinements with EXAFS and artificially prepared rough multilayers indicates
that this type of approach give a reliable and speedy determination of the roughness, interdiffusion
and lattice parameter variations in multilayers. This work has been described in a number of papers
in the last few years.
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