CSIC - Institute of Optics

Madrid, Spain

CSIC - Institute of Optics

Madrid, Spain
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Manjavacas A.,CSIC - Institute of Optics | Abajo F.J.G.D.,CSIC - Institute of Optics | Nordlander P.,Rice University
Nano Letters | Year: 2011

We present a fully quantum mechanical approach to describe the coupling between plasmons and excitonic systems such as molecules or quantum dots. The formalism relies on Zubarev's Green functions, which allow us to go beyond the perturbative regime within the internal evolution of a plasmonic nanostructure and to fully account for quantum aspects of the optical response and Fano resonances in plasmon - excition (plexcitonic) systems. We illustrate this method with two examples consisting of an exciton-supporting quantum emitter placed either in the vicinity of a single metal nanoparticle or in the gap of a nanoparticle dimer. The optical absorption of the combined emitter - dimer structure is shown to undergo dramatic changes when the emitter excitation level is tuned across the gap-plasmon resonance. Our work opens a new avenue to deal with strongly interacting plasmon - excition hybrid systems. © 2011 American Chemical Society.

Koppens F.H.L.,ICFO - Institute of Photonic Sciences | Chang D.E.,California Institute of Technology | Garcia De Abajo F.J.,CSIC - Institute of Optics | Garcia De Abajo F.J.,University of Southampton
Nano Letters | Year: 2011

Graphene plasmons provide a suitable alternative to noble-metal plasmons because they exhibit much tighter confinement and relatively long propagation distances, with the advantage of being highly tunable via electrostatic gating. Here, we propose to use graphene plasmons as a platform for strongly enhanced light-matter interactions. Specifically, we predict unprecedented high decay rates of quantum emitters in the proximity of a carbon sheet, observable vacuum Rabi splittings, and extinction cross sections exceeding the geometrical area in graphene nanoribbons and nanodisks. Our theoretical results provide the basis for the emerging and potentially far-reaching field of graphene plasmonics, offering an ideal platform for cavity quantum electrodynamics, and supporting the possibility of single-molecule, single-plasmon devices. © 2011 American Chemical Society.

Kuttge M.,FOM Institute for Atomic and Molecular Physics | Garcia De Abajo F.J.,CSIC - Institute of Optics | Polman A.,FOM Institute for Atomic and Molecular Physics
Nano Letters | Year: 2010

We study the resonant modes of nanoscale disk resonators sustaining metal-insulator-metal (MIM) plasmons and demonstrate the versatility of these cavities to achieve ultrasmall cavity mode volume. Ag/SiO 2/Ag MIM structures were made by thin-film deposition and focused ion beam milling with cavity diameters that ranged from d = 65-2000 nm. High-resolution two-dimensional cavity-mode field distributions were determined using cathodoluminescence imaging spectroscopy and are in good agreement with boundary element calculations. For the smallest cavities (d = 65-140 nm), the lowest order mode (m = 1, n = 1) is observed in the visible spectral range. This mode is of similar nature as the one in plasmonic particle dimers, establishing a natural connection between localized and traveling plasmon cavities. A cavity quality factor of Q = 16 is observed for the 105 nm diameter cavity, accompanied by a mode volume as small as 0.00033λ0 3. The corresponding Purcell factor is 900, making these ultrasmall disk resonators ideal candidates for studies of enhanced spontaneous emission and lasing. © 2009 American Chemical Society.

Manjavacas A.,CSIC - Institute of Optics | Garcia De Abajo F.J.,CSIC - Institute of Optics
Physical Review Letters | Year: 2010

We study the frictional torque acting on particles rotating in empty space. At zero temperature, vacuum friction transforms mechanical energy into light emission and produces particle heating. However, particle cooling relative to the environment occurs at finite temperatures and low rotation velocities. Radiation emission is boosted and its spectrum significantly departed from a hot-body emission profile as the velocity increases. Stopping times ranging from hours to billions of years are predicted for materials, particle sizes, and temperatures accessible to experiment. Implications for the behavior of cosmic dust are discussed.

Yamamoto N.,Tokyo Institute of Technology | Ohtani S.,Tokyo Institute of Technology | Garcia De Abajo F.J.,CSIC - Institute of Optics
Nano Letters | Year: 2011

We study the plasmons confined at the gap between silver nanospheres and silver planar surfaces by means of angle- and space-resolved spectral cathodoluminescence. Plasmons in individual nanoparticles are excited by an electron beam, giving rise to light emission that is analyzed as a function of photon-energy, emission direction, and position of the beam spot. Gap plasmons are significantly red shifted due to the interaction between the particles and the metal substrate, and they are preferentially excited by positioning the beam close to the sphere centers, which results in an angular emission pattern similar to that of a dipole oriented along the surface normal. In contrast, weaker emission features are observed at higher-energies when the beam is grazing to the spheres, corresponding to the excitation of Mie plasmons like those of isolated particles, which display an angular pattern approximately mimicking a dipole parallel to the surface. Our measurements are in excellent agreement with simulations, thus providing useful insight into gap plasmons arising from the interaction between metal particles and metal substrates that are relevant for molecular sensing applications. © 2011 American Chemical Society.

David C.,CSIC - Institute of Optics | Garcia De Abajo F.J.,CSIC - Institute of Optics
Journal of Physical Chemistry C | Year: 2011

Spatial nonlocality is known to play an important role in nano-optics when small nanometer-sized structures are involved, but few efforts have been made to assess nonlocal effects in a rigorous way. We present two different approaches to account for nonlocality in metal nanoparticles: (i) the nonretarded specular reflection model and (ii) the retarded hydrodynamical model. Excellent agreement with available experiments is obtained from our parameter-free simulations, which lead to dramatic differences with respect to local theory. Both models predict sizable plasmon blue shifts and broadenings in individual metal nanoparticles, nanoshells, particle dimers, and Yagi-Uda antennas. An analysis of plasmon resonances for varying particle size and spacing allows us to separate nonlocal and retardation effects within the hydrodynamical model. We find a wide range of geometrical parameters for which nonlocal effects coexist with significant retardation. This study is particularly relevant for broad, active areas involving applications of local field enhancement to biosensing and nonlinear optics in plasmonics. © 2011 American Chemical Society.

Garcia De Abajo F.J.,CSIC - Institute of Optics
Reviews of Modern Physics | Year: 2010

This review discusses how low-energy valence excitations created by swift electrons can render information on the optical response of structured materials with unmatched spatial resolution. Electron microscopes are capable of focusing electron beams on subnanometer spots and probing the target response either by analyzing electron energy losses or by detecting emitted radiation. Theoretical frameworks suited to calculate the probability of energy loss and light emission (cathodoluminescence) are reconsidered and compared with experimental results. More precisely, a quantum-mechanical description of the interaction between the electrons and the sample is discussed, followed by a powerful classical dielectric approach that can be applied in practice to more complex systems. The conditions are assessed under which classical and quantum-mechanical formulations are equivalent. The excitation of collective modes such as plasmons is studied in bulk materials, planar surfaces, and nanoparticles. Light emission induced by the electrons is shown to constitute an excellent probe of plasmons, combining subnanometer resolution in the position of the electron beam with nanometer resolution in the emitted wavelength. Both electron energy-loss and cathodoluminescence spectroscopies performed in a scanning mode of operation yield snapshots of plasmon modes in nanostructures with fine spatial detail as compared to other existing imaging techniques, thus providing an ideal tool for nanophotonics studies. © 2010 The American Physical Society.

Kling S.,CSIC - Institute of Optics | Marcos S.,CSIC - Institute of Optics
Journal of Refractive Surgery | Year: 2013

PURPOSE: To evaluate corneal deformation with varying intraocular pressure and the dependency of the biomechanical response on the corneal hydration state, modulated by the storage solutions or postmortem period. METHODS: Thirty fresh enucleated porcine eyes were used for in vitro whole eye globe inflation experiments. The eyes were separated into five groups and treated with different solutions: 20% dextran, 8% dextran, 0.125% riboflavin-20% dextran, Optisol-GS (Bausch & Lomb, Rochester, NY), and one control group of virgin (untreated) eyes. Intraocular pressure was increased (from 15 to 55 mm Hg) and decreased (to 15 mm Hg) in 5-mm Hg steps and Scheimpflug images were taken at each step. Measurements were repeated after 24 hours. Thickness and curvature changes were analyzed as a function of intraocular pressure. RESULTS: Corneal deformation differed across conditions and hydration states. Dehydration by any dextran solution increased the hysteresis after the inflation/deflation cycle (14.29 vs 22.07 to 41.75 μm), whereas overnight hydration did not lead to a significant difference. Compared to control corneas, corneas treated with Optisol-GS showed the most similar behavior. Corneas treated with 0.125% riboflavin-20% dextran deformed most (Δthicknessmax = 38.27 μm), indicating a softening of the corneal tissue compared to control corneas (23.18 μm) and corneas treated with 8% dextran (21.01 μm) and 20% dextran (29.07 μm). Dextran instillation decreased corneal thickness on average to 56.5% at 0 hours and 72.7% at 24 hours. CONCLUSIONS: Corneal hydration and tissue preservation changed corneal biomechanics, in particular its relaxation over a period of 24 hours. Copyright © SLACK Incorporated.

Kling S.,CSIC - Institute of Optics | Marcos S.,CSIC - Institute of Optics
Investigative Ophthalmology and Visual Science | Year: 2013

PURPOSE. Air puff systems have been presented recently to measure corneal biomechanical properties in vivo. In our study we tested the influence of several factors on corneal deformation to an air puff: IOP, corneal rigidity, dehydration, presence of sclera, and in vivo versus in vitro conditions. METHODS. We used 14 freshly enucleated porcine eyes and five human donor eyes for in vitro experiments; nine human eyes were used for in vivo experiments. Corneal deformation was studied as a function of: IOP ranging from 15 to 45 mm Hg (in vitro); dehydration after riboflavin-dextran instillation (in vitro); corneal rigidity after standard ultraviolet (UV) corneal crosslinking (CXL, in vitro); boundary conditions, that is effect of the presence of the sclera (comparing corneal buttons and whole globes in vitro in pigs); and effect of ocular muscles (comparing human whole globes in vitro and in vivo). The temporal corneal deformation was characterized by the apex indentation across time, the maximal indentation depth, and the temporal symmetry (comparing inward versus outward deformation). The spatial corneal profile was characterized by the peak distance at maximal deformation. RESULTS. Temporal and spatial deformation profiles were very sensitive to the IOP (P < 0.001). The sclera slightly affected the temporal symmetry, while the ocular muscles drastically changed the amount of corneal recovery. CXL produced a significant (P=0.001) reduction of the cornea indentation (by a factor of 1.41), and a change in the temporal symmetry of the corneal deformation profile (by a factor of 1.65), indicating a change in the viscoelastic properties with treatment. CONCLUSIONS. Corneal deformation following an air puff allows the measurement of dynamic properties, which are essential for the characterization of corneal biomechanics. © 2013 The Association for Research in Vision and Ophthalmology, Inc.

Toudert J.,CSIC - Institute of Optics
Nanotechnology Reviews | Year: 2014

Spectroscopic ellipsometry (SE) is a powerful technique for the characterization of materials, which is able to probe in a sensitive way their nanostructure as well as to get rich information about their dielectric properties, through the interaction of polarized light with matter. In the present trend of developing functional advanced materials of increasing complexity for a wide range of technological applications, works involving SE have flourished and have been reported in an increasing number of articles, reviews, and books. In this context, the aim of this paper is to provide for those among material scientists who are not SE specialists, a concise and updated overview of the capabilities of SE for the characterization of the so-called nano- and metamaterials, especially those presenting active functionalities. Key aspects for a reliable material characterization by SE are given: choice of the setup and measurement conditions, measurement accuracy, definition of a model, sensitivity to parameters. Also, very recent works involving SE are highlighted, especially those dealing with the development of building block materials for optimized or active plasmonics applications, the still ongoing exploration of small-size effects on the dielectric response of matter, the characterization of metamaterials, and the design of detectors with improved accuracy based on coupling of the phase sensitivity of SE with metamaterials engineering.

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