- School of Physics - Research Publications
School of Physics - Research Publications
Permanent URI for this collection
10 results
Filters
Reset filtersSettings
Statistics
Citations
Search Results
Now showing
1 - 10 of 10
-
ItemPlasmonic Metasurfaces for Optical Information ProcessingWesemann, L ; Panchenko, E ; Singh, K ; Gomez, DE ; Davis, TJ ; Roberts, A ; Simpson, MC ; Juodkazis, S (SPIE-INT SOC OPTICAL ENGINEERING, 2019-01-01)Optical spatial frequency filtering is a key method for information processing in biological and technical imaging. While conventional approaches rely on bulky components to access and filter the Fourier plane content of a wavefield, nanophotonic approaches for spatial frequency filtering have recently gained attention. Here computational and experimental progress towards the design and demonstration of metasurfaces with spatial frequency filtering capability for optical image processing will be presented. Using the example of a metasurface consisting of radial rod trimers we demonstrate its potential to perform edge enhancement in an amplitude image and conversion of phase gradients in a wavefield into intensity modulations. The presented results indicate a potential avenue for ultra-compact image processing devices with applications in biological live-cell imaging.
-
ItemTuning the asymmetric response of metasurfaces for optical spatial filteringDavis, TJ ; Eftekhari, F ; Gomez, DE ; Roberts, A ; Mitchell, A ; RubinszteinDunlop, H (SPIE-INT SOC OPTICAL ENGINEERING, 2019-01-01)The spatial filtering of optical signals has been demonstrated previously with metasurface thin-films created from arrays of structured optical elements. We consider the problem of changing the symmetry of their response with changes to the in-plane wavevector kI→-kI and show it can be tailored or even dynamically tuned. Our work is based on a general theory of metasurfaces constructed from non-diffracting arrays of coupled metal particles. We present the optical transfer function of such a metasurface, identify the physical properties essential for asymmetry and demonstrate its behaviour experimentally.
-
ItemUltracompact Camera Pixel with Integrated Plasmonic Color FiltersPanchenko, E ; Wesemann, L ; Gomez, DE ; James, TD ; Davis, T ; Roberts, A (WILEY-V C H VERLAG GMBH, 2019-09-17)Photodetector size imposes a fundamental limit on the amount of information that can be recorded by an image sensor. Compact, high-resolution sensors are generally preferred for portable electronic devices such as mobile phones and digital cameras, and as a result, a significant effort has been invested in improving the image quality provided by small-area image sensors. Reducing photodetector size, however, still faces challenges in implementation requiring improvements in current technology to meet the demand for ultracompact imaging systems such as cameras. An issue with a decrease in size is associated with photodetectors utilizing color filters. In most commonly used camera designs these filters are made of dyes or pigments and incompatible with the complementary metal-oxide-semiconductor fabrication process. They are, therefore, fabricated in two different technological processes and require subsequent alignment. As the pixel size decreases, the alignment of these layers becomes challenging. Furthermore, dye-based filters need to have a thickness of the order of micrometers to ensure sufficient absorption. Here a compact, low-cost color sensor is proposed and experimentally demonstrated utilizing monolithically integrated plasmonic antennas that have a nanoscale thickness and are fabricated in the same technological process with photodetector matrix.
-
ItemPlasmene Metasurface Absorbers: Electromagnetic Hot Spots and Hot CarriersShi, Q ; Connell, TU ; Xiao, Q ; Chesman, ASR ; Cheng, W ; Roberts, A ; Davis, TJ ; Gomez, DE (AMER CHEMICAL SOC, 2019-02-01)Light-matter interactions are extremely important, as they sustain life on Earth and can be tailored for diverse applications in areas such as solar energy conversion, chemical sensing, and information storage. One key process of these interactions is the absorption of photons. We demonstrate a novel material capable of absorbing up to 98% of incident visible light. The material comprises a thin sheet of a tightly packed two-dimensional lattice of metal nanoparticles, called plasmene, supported by a thin (subwavelength) dielectric film deposited on top of a mirror. We demonstrate how the resulting metasurface absorbers are useful in surface-enhanced spectroscopy and in the generation of plasmonic hot carriers. These structures hold great promise for applications in structural color, sensing, and photocatalysis.
-
ItemLarge-Area Nanofabrication of Partially Embedded Nanostructures for Enhanced Plasmonic Hot-Carrier ExtractionNg, C ; Zeng, P ; Lloyd, JA ; Chakraborty, D ; Roberts, A ; Smith, TA ; Bach, U ; Sader, JE ; Davis, TJ ; Gomez, DE (AMER CHEMICAL SOC, 2019-03-01)When plasmonic nanoparticles are coupled with semiconductors, highly energetic hot carriers can be extracted from the metal-semiconductor interface for various applications in light energy conversion. However, the current quantum yields for hot-electron extraction are generally low. An approach for increasing the extraction efficiency consists of maximizing the contact area between the surface of the metal nanostructure and the electron-accepting material. In this work, we developed an innovative, simple, and scalable fabrication technique that partially embeds colloidal plasmonic nanostructures within a semiconductor TiO2 layer without utilizing any complex top-down nanofabrication method. The successful embedding is confirmed by scanning electron microscopy and atomic force microscopy imaging. Using visible-pump, near-IR probe transient absorption spectroscopy, we also provide evidence that the increase in the surface contact area between the nanostructures and the electron-accepting material leads to an increase in the amount of hot-electron injection into the TiO2 layer.
-
ItemMetasurfaces with Asymmetric Optical Transfer Functions for Optical Signal ProcessingDavis, TJ ; Eftekhari, F ; Gomez, DE ; Roberts, A (AMER PHYSICAL SOC, 2019-07-01)Metasurface thin films created from arrays of structured optical elements have been shown to perform spatial filtering of optical signals. To extend their usefulness it is important that the symmetry of their response with changes to the in-plane wave vector k_{p}→-k_{p} can be tailored or even dynamically tuned. In this Letter we use a general theory of metasurfaces constructed from nondiffracting arrays of coupled metal particles to derive the optical transfer function and identify the physical properties essential for asymmetry. We validate our theory experimentally showing how the asymmetric response of a two-dimensional (planar) metasurface can be optically tuned. Our results set the direction for future developments of metasurfaces for optical signal processing.
-
ItemOptical image processing with metasurface dark modesRoberts, A ; Gomez, DE ; Davis, TJ (OPTICAL SOC AMER, 2018-09-01)Here we consider image processing using the optical modes of metasurfaces with an angle-dependent excitation. These spatially dispersive modes can be used to directly manipulate the spatial frequency content of an incident field, suggesting their use as ultra-compact alternatives for analog optical information processing. A general framework for describing the filtering process in terms of the optical transfer functions is provided. In the case where the relevant mode cannot be excited with a normally incident plane wave (a dark mode), high-pass filtering is obtained. We provide examples demonstrating filtering of both amplitude and pure phase objects.
-
ItemPlasmonic Near-Complete Optical Absorption and Its ApplicationsNg, C ; Wesemann, L ; Panchenko, E ; Song, J ; Davis, TJ ; Roberts, A ; Gomez, DE (WILEY-V C H VERLAG GMBH, 2019-07-01)Near-complete absorption of light has the potential to underpin advances in photodetection, advanced chemistry, coloration of materials, and energy. This review paper reports recent progress on the development of metasurfaces and thin film structures that produce strong absorption bands in the visible and longer wavelength regions of the electromagnetic spectrum, due in part to the excitation of plasmonic resonances. Proof-of-concept demonstrations are discussed for applications of these in chemical sensing, the generation of structural color, the creation of optoelectronic devices, and photocatalysis. Emerging future applications are also discussed.
-
ItemMetasurfaces, dark modes, and high NA illuminationWesemann, L ; Achmari, P ; Singh, K ; Panchenko, E ; James, TD ; Gomez, DE ; Davis, TJ ; Roberts, A (OPTICAL SOC AMER, 2018-10-15)The interaction of a focused beam with a metasurface supporting dark modes is investigated. We show computationally and experimentally that the excitation of dark modes is accompanied by characteristic changes in the reflected Fourier spectrum. This spatial frequency filtering capability indicates an avenue for the all-optical, on-chip detection of phase gradients for biological and other imaging techniques.
-
ItemSelective near-perfect absorbing mirror as a spatial frequency filter for optical image processingWesemann, L ; Panchenko, E ; Singh, K ; Della Gaspera, E ; Gomez, DE ; Davis, TJ ; Roberts, A (AMER INST PHYSICS, 2019-10-01)Spatial frequency filtering is a fundamental enabler of information processing methods in biological and technical imaging. Most filtering methods, however, require either bulky and expensive optical equipment or some degree of computational processing. Here, we experimentally demonstrate real-time, on-chip, all-optical spatial frequency filtering using a thin-film perfect absorber structure. We experimentally demonstrate edge enhancement of an amplitude image and conversion of phase gradients to intensity modulation in an image. The device is used to demonstrate enhancement of an image of pond algae.