Argia txiki egiten denean

A brief historical perspective on the concept of light is introduced, focusing on some of the aspects derived from its ondulatory nature, which determines many of the properties of light-matter interaction within the electrodynamical theory. The ondulatory nature of light sets up a diffraction limit, which prevents standard localization of light below half a micrometer. The use of metallic nanoparticles, and the excitations of their conduction electrons with the generation of electronic surface charge density waves, so-called plasmons, allows for bringing the energy and momentum of light down to sub-diffraction dimensions. Metallic nanostructures are shown to act as effective optical nanoantennas which capture and emit light, opening photonics to the realm of the nanoscale. Examples of technological application of optical nanoantennas in the fields of optical nanoscopy, surface-enhanced molecular spectroscopy, oncological therapy, energy havesting, metamaterials and information technologies are discussed.; Argiaren kontzeptuari buruzko perspektiba historiko laburra aurkezten da artikulu honetan, haren uhin-izaera azpimarratuz. Uhin-izaera honek materiaren eta argiaren arteko elkarrekintzaren zenbait ezaugarri finkatzen ditu teoria elektromagnetikoaren barruan. Horien artean, aipatzekoa da difrakzio-muga, mikrometro erdi baten azpitik argia lokalizatzea ahalbidetzen ez duena. Metalezko nanopartikulek haien elektroi eroaleen kitzikapenaren bitartez, gainazaleko karga-dentsitatearen uhinak (plasmoiak) sortzen dituzte, eta, horiei esker, argia difrakzio azpiko dimentsioetara eramatea lortzen da. Metalezko nanoegiturek argia harrapatzen eta igortzen duten nanoantena moduko portaera azaltzen dute, fotonika nanoeskalaren erresumara eramanez. Testuinguru honetan, nanoantena optikoen aplikazio teknologikoetako batzuk erakusten dira zenbait arlotan: besteak beste, nanoskopia optikoan, gainazalek handitutako espektroskopia molekularrean, terapia onkologikoan, energi metaketan, metamaterialetan, edota informazioaren teknologietan

Nonlinear Optical Response of a Plasmonic Nanoantenna to Circularly Polarized Light: Rotation of Multipolar Charge Density and Near-Field Spin Angular Momentum Inversion

The spin and orbital angular momentum carried by electromagnetic pulses open new perspectives to control nonlinear processes in light–matter interactions, with a wealth of potential applications. In this work, we use time-dependent density functional theory (TDDFT) to study the nonlinear optical response of a free-electron plasmonic nanowire to an intense, circularly polarized electromagnetic pulse. In contrast to the well-studied case of the linear polarization, we find that the nth harmonic optical response to circularly polarized light is determined by the multipole moment of order n of the induced nonlinear charge density that rotates around the nanowire axis at the fundamental frequency. As a consequence, the frequency conversion in the far field is suppressed, whereas electric near fields at all harmonic frequencies are induced in the proximity of the nanowire surface. These near fields are circularly polarized with handedness opposite to that of the incident pulse, thus producing an inversion of the spin angular momentum. An analytical approach based on general symmetry constraints nicely explains our numerical findings and allows for generalization of the TDDFT results. This work thus offers new insights into nonlinear optical processes in nanoscale plasmonic nanostructures that allow for the manipulation of the angular momentum of light at harmonic frequencies.We acknowledge financial support from project IT1526–22 of the Department of Education of the Basque Government, and projects PID2019–107432GB-I00 and PID2022–139579NB-I00, funded by MCIN/AEI/10.13039/501100011033 and “FEDER Una manera de hacer Europa”

Dispersive surface-response formalism to address nonlocality in extreme plasmonic field confinement

The surface-response formalism (SRF), where quantum surface-response corrections are incorporated into the classical electromagnetic theory via the Feibelman parameters, serves to address quantum effects in the optical response of metallic nanostructures. So far, the Feibelman parameters have been typically obtained from many-body calculations performed in the long-wavelength approximation, which neglects the nonlocality of the optical response in the direction parallel to the metal–dielectric interface, thus preventing to address the optical response of systems with extreme field confinement. To improve this approach, we introduce a dispersive SRF based on a general Feibelman parameter d ⊥(ω, k ‖), which is a function of both the excitation frequency, ω, and the wavenumber parallel to the planar metal surface, k ‖. An explicit comparison with time-dependent density functional theory (TDDFT) results shows that the dispersive SRF correctly describes the plasmonic response of planar and nonplanar systems featuring extreme field confinement. This work thus significantly extends the applicability range of the SRF, contributing to the development of computationally efficient semiclassical descriptions of light–matter interaction that capture quantum effects.MCIN/AEI/10.13039/501100011033/ (PID2019-107432GB-I00); Department of Education of the Basque Government (IT1526-22); “Investissements d’Avenir” LabEx PALM (ANR-10-LABX-0039-PALM)

A Novel Vibrational Spectroscopy Using Spintronic-Plasmonic Antennas: Magneto-Refractive Surface-Enhanced Infrared Absorption

We present experimental and theoretical results of the molecular sensing performance of a novel platform based on magnetic modulation of surface-enhanced infrared absorption spectroscopy. For this, we study the effect that molecular infrared vibrations of a PMMA layer have on the optical and magneto-refractive response of spintronic antennas. Specifically, a periodic array of rods is fabricated from giant-magneto-resistance Au/Ni81Fe19 metallic multilayers, and the effect of depositing a layer of PMMA on top of the array is investigated from both experimental and theoretical points of view. We find that the relative changes induced by the infrared vibrations of PMMA on the magneto-refractive signal are larger than the relative changes induced on the optical transmission. This result indicates that the magneto-refractive response is more sensitive to the excitation of molecular vibrations than the optical response and fosters the development of a novel type of an infrared sensing technique based on spintronic antennas: Magneto-Refractive Surface-Enhanced Infrared Absorption (SEIRA) Spectroscopy.We acknowledge financial support from MINECO through projects AMES (No. MAT 2014-58860-P), Quantum Spin Plasmonics (No. FIS2015-72035-EXP), and MIRRAS (No. MAT2017-84009-R) and Comunidad de Madrid (CM) through project SINOXPHOS-CM (No. S2018/BAA-4403). We acknowledge the service from the MiNa Laboratory at IMN and funding from MINECO under Project No. CSIC13-4E-1794 and from CM under Project No. S2013/ICE-2822 (Space-Tec), both with support from EU (FEDER, FSE). L.B., N.Z., and J.A. acknowledge support from the Department of Education, Research and Universities of the Basque Government through Project Ref. No. IT-1164-19, the Department of Industry of the Basque Government through Project No. KK-2018/00001, and the Spanish MICIN through Project Ref. No. PID2019-107432GB-I0

Complex plasmon-exciton dynamics revealed through quantum dot light emission in a nanocavity

Plasmonic cavities can confine electromagnetic radiation to deep sub-wavelength regimes. This facilitates strong coupling phenomena to be observed at the limit of individual quantum emitters. Here, we report an extensive set of measurements of plasmonic cavities hosting one to a few semiconductor quantum dots. Scattering spectra show Rabi splitting, demonstrating that these devices are close to the strong coupling regime. Using Hanbury Brown and Twiss interferometry, we observe non-classical emission, allowing us to directly determine the number of emitters in each device. Surprising features in photoluminescence spectra point to the contribution of multiple excited states. Using model simulations based on an extended Jaynes-Cummings Hamiltonian, we find that the involvement of a dark state of the quantum dots explains the experimental findings. The coupling of quantum emitters to plasmonic cavities thus exposes complex relaxation pathways and emerges as an unconventional means to control dynamics of quantum states.S.N.G. thanks the Government of Israel for a Planning and Budgeting Committee Fel-lowship. G.H. is the incumbent of the Hilda Pomeraniec Memorial Professorial Chair.R.E., T.N. and J.A. acknowledge funding from projects FIS2016-80174-P and PID2019-107432GB-I00 of the Spanish Ministry of Science, Innovation and Universities MICINN,as well as funding from grant IT1164-19 for consolidated groups of the Basque Uni-versity, through the Department of Universities of the Basque Government. This projectreceived partial support from the European Union’s Horizon 2020 research and inno-vation programme under grant agreement no. 861950, project POSEIDON, and grantagreement no. 810626, project SINNCE. We thank Garnett W. Bryant and PeterNordlander for stimulating discussion

Complex plasmon-exciton dynamics revealed through quantum dot light emission in a nanocavity

Plasmonic cavities can confine electromagnetic radiation to deep sub-wavelength regimes. This facilitates strong coupling phenomena to be observed at the limit of individual quantum emitters. Here, we report an extensive set of measurements of plasmonic cavities hosting one to a few semiconductor quantum dots. Scattering spectra show Rabi splitting, demonstrating that these devices are close to the strong coupling regime. Using Hanbury Brown and Twiss interferometry, we observe non-classical emission, allowing us to directly determine the number of emitters in each device. Surprising features in photoluminescence spectra point to the contribution of multiple excited states. Using model simulations based on an extended Jaynes-Cummings Hamiltonian, we find that the involvement of a dark state of the quantum dots explains the experimental findings. The coupling of quantum emitters to plasmonic cavities thus exposes complex relaxation pathways and emerges as an unconventional means to control dynamics of quantum states.S.N.G. thanks the Government of Israel for a Planning and Budgeting Committee Fel-lowship. G.H. is the incumbent of the Hilda Pomeraniec Memorial Professorial Chair.R.E., T.N. and J.A. acknowledge funding from projects FIS2016-80174-P and PID2019-107432GB-I00 of the Spanish Ministry of Science, Innovation and Universities MICINN,as well as funding from grant IT1164-19 for consolidated groups of the Basque Uni-versity, through the Department of Universities of the Basque Government. This projectreceived partial support from the European Union’s Horizon 2020 research and inno-vation programme under grant agreement no. 861950, project POSEIDON, and grantagreement no. 810626, project SINNCE. We thank Garnett W. Bryant and PeterNordlander for stimulating discussion

Remote near-field spectroscopy of vibrational strong coupling between organic molecules and phononic nanoresonators

Vibrational strong coupling (VSC) promises ultrasensitive IR spectroscopy and modification of material properties. Here, nanoscale mapping of VSC between organic molecules and individual IR nanoresonators is achieved by remote near-field spectroscopy. Phonon polariton (PhP) nanoresonators can dramatically enhance the coupling of molecular vibrations and infrared light, enabling ultrasensitive spectroscopies and strong coupling with minute amounts of matter. So far, this coupling and the resulting localized hybrid polariton modes have been studied only by far-field spectroscopy, preventing access to modal near-field patterns and dark modes, which could further our fundamental understanding of nanoscale vibrational strong coupling (VSC). Here we use infrared near-field spectroscopy to study the coupling between the localized modes of PhP nanoresonators made of h-BN and molecular vibrations. For a most direct probing of the resonator-molecule coupling, we avoid the direct near-field interaction between tip and molecules by probing the molecule-free part of partially molecule-covered nanoresonators, which we refer to as remote near-field probing. We obtain spatially and spectrally resolved maps of the hybrid polariton modes, as well as the corresponding coupling strengths, demonstrating VSC on a single PhP nanoresonator level. Our work paves the way for near-field spectroscopy of VSC phenomena not accessible by conventional techniques.This work was supported by the MCIN/AEI/10.13039/501100011033 under the María de Maeztu Units of Excellence Program (CEX2020-001038-M) and the Projects RTI2018-094830-B-100, PID2021-123949OB-I00, PID2019-107432GB-I00 and PID2021-122511OB-I00, as well as by the Graphene Flagship (GrapheneCore3, No. 881603). J.L. and J.H.E. are grateful for support from the Office of Naval Research (Award No. N00014-20-1-2474), for the BN crystal growth. S.V. acknowledges financial support by the Comunidad de Madrid through the Atracción de Talento program (grant no. 2020-T1/IND-20041). C.M.-E., R.E., and J.A. received funding from grant no. IT 1526-22 from the Basque Government for consolidated groups of the Basque University