1 Active surfaces in microwave and THz,
The general aim of the first part of the proposal is to fabricate active surfaces to control intensity, phase and polarization of electromagnetic waves in microwave and terahertz frequencies. We have demonstrated four specific work in this part.
1.1 Graphene based Electrically Switchable Metadevices: Here, integrating passive metamaterials with active graphene devices, we demonstrated a new class of electrically controlled metadevices. These metadevices enable efficient control of both amplitude (> 50 dB) and phase (> 90°) of electromagnetic waves.
Ref: Science Advances, (DOI: 10.1126/sciadv.aao1749)
1.2 Controlling phase of microwaves with active graphene surfaces
In this work, we developed a method to control the reflection phase of microwaves using electrically tunable graphene devices. This device structure yields electrically tunable resonance absorbance and step-like phase shift around the resonance frequency when the impedance of graphene matches with the free space impedance.
Ref: Applied Physics Letters, (doi: 10.1063/1.4980087)
1.3 Observation of Gate-Tunable Coherent Perfect Absorption of Terahertz Radiation in Graphene: We report the experimental observation of electrically tunable coherent perfect absorption (CPA) of terahertz (THz) radiation in graphene. W Ref: ACS Photonics , (doi: 10.1021/acsphotonics.6b00240)
1.4 Graphene based terahertz phase modulators
Here, we demonstrate an efficient terahertz phase and amplitude modulation using electrically tunable graphene devices. Our device structure consists of electrolyte-gated graphene placed at quarter wavelength distance from a reflecting metallic surface. Terahertz time domain reflection spectroscopy reveals the voltage controlled phase modulation of 2pi and the reflection modulation of 50 dB. Ref: 2D Materials , (doi: 10.1088/2053-1583/aabfaa)
1.5 Graphene based topological devices: Through use of graphene-based devices, we demonstrate the emergence of EPs in an electrically controlled interaction between light and a collection of organic molecules in the terahertz regime at room temperature. We show that the intensity and phase of terahertz pulses can be controlled by a gate voltage, which drives the device across the EP. Ref: Science (DOI: 10.1126/science.abn6528)
2 Active thermal (infrared) surfaces: The general aim of the second part of the proposal is to develop a new class of active thermal surfaces capable of efficient real-time control of its thermal emissivity over full infrared spectrum without changing its temperature.
2.1 Graphene Based Adaptive Thermal Camouflage: Here we report a new class of active thermal surfaces capable of efficient real-time electrical-control of thermal emission over the full infrared (IR) spectrum without changing the temperature of the surface. Our approach relies on electro-modulation of IR absorptivity and emissivity of multilayer graphene via reversible intercalation of nonvolatile ionic liquids. Ref: Nano Letters , (doi: 10.1021/acs.nanolett.8b01746)
3 Active optical surfaces in the visible: The aim of the third part of the project is to realise graphene-based devices in the visible spectrum. This is a very challenging task which requires to achieve extreme charge densities on graphene. We have demonstrated four specific work in this part.
3.1 Graphene-enabled optoelectronics on paper : Here, we demonstrate a new class of optoelectronic devices on a piece of printing paper using graphene as an electrically reconfigurable optical medium. Our approach relies on electro-modulation of optical properties of multilayer graphene on paper via blocking the interband electronic transitions. The paper-based devices yield high optical contrast in the visible spectrum with fast response speed. Ref: ACS Photonics , (doi: 10.1021/acsphotonics.6b00017)
3.2 Graphene-Quantum Dot Hybrid Optoelectronics at Visible Wavelengths: Here, we report a unique approach that avoids these limitations and implements graphene into optoelectronic devices working in the visible spectrum. The approach relies on controlling nonradiative energy transfer between colloidal quantum-dots and graphene through gate-voltage induced tuning of the charge density of graphene. Ref: ACS Photonics , (doi: 10.1021/acsphotonics.8b00163)
3.3 Graphene as a reversible and spectrally selective fluorescence quencher: We report reversible and spectrally selective fluorescence quenching of quantum dots (QDs) placed in close proximity to graphene. Controlling interband electronic transitions of graphene via electrostatic gating greatly modifies the fluorescence lifetime and intensity of nearby QDs via blocking of the nonradiative energy transfer between QDs and graphene. Ref: Scientific Reports, (doi: 10.1038/srep33911)
3.4 Generation of sub-20-fs pulses from a graphene mode-locked laser: In this work, we used our graphene devices to realize new type of mode-locked lases. We demonstrate the shortest pulses directly generated to date from a solid-state laser, mode locked with a graphene saturable absorber (GSA). In the experiments, a low-threshold diode-pumped Cr3+:LiSAF laser was used near 850 nm. Ref: Optics Express, (doi: 10.1364/OE.25.002834)
3.5 Multispectral optical surfaces: Here, we report graphene-based electro-optical devices with unprecedented optical tunability covering the entire electromagnetic spectrum from the visible to microwave. Ref: Nature Photonics, (
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