1,720,966 research outputs found
Quantum theory of longitudinal-transverse polaritons in nonlocal thin films
No full textWhen midinfrared light interacts with nanoscale polar dielectric structures, optical phonon propagation cannot be ignored, leading to a rich nonlocal phenomenology that we have only recently started to uncover. In properly crafted nanodevices this includes the creation of polaritonic excitations with hybrid longitudinal-transverse nature, which are predicted to allow energy funneling from longitudinal electrical currents to far-field transverse radiation. In this work we study the physics of these longitudinal-transverse polaritons in a dielectric nanolayer in which the nonlocality strongly couples epsilon-near-zero modes to longitudinal phonons. After having calculated the system’s spectrum solving Maxwell’s equations, we develop an analytical polaritonic theory able to transparently quantify the nonlocality-mediated coupling as a function of the system parameters. Such a theory provides a powerful tool for the study of longitudinal-transverse polariton interactions and we use it to determine the conditions required for the hybrid modes to appear
Theory of four-wave-mixing in phonon polaritons
No full textThird order anharmonic scattering in light–matter systems can drive a wide variety of practical and physically interesting processes from lasing to polariton condensation. Motivated by recent experimental results in the nonlinear optics of localized phonon polaritons, in this Letter we develop a quantum theory capable of describing four-wave mixing in arbitrarily inhomogeneous photonic environments. Using it, we investigate Kerr self-interaction and parametric scattering of surface and localized phonon polaritons, showing both processes to be within experimental reach
Surface phonon polaritons for infrared optoelectronics
No full textIn recent years, there has been significant fundamental research into surface phonon polaritons, owing to their ability to compress light to extremely small dimensions, low losses, and the ability to support anisotropic propagation. In this Perspective, after briefly reviewing the present state of mid-infrared optoelectronics, we will assess the potential of surface phonon polariton-based nanophotonics for infrared (3-100 μm) light sources, detectors, and modulators. These will operate in the Reststrahlen region where conventional semiconductor light sources become ineffective. Drawing on the results from the past few years, we will sketch some promising paths to create such devices and we will evaluate their practical advantages and disadvantages when compared to other approaches to infrared optoelectronics.</p
Non-equilibrium electrical generation of surface phonon polaritons
No full textNotwithstanding its relevance to many applications in sensing, security, and communications, electrical generation of narrow-band mid-infrared light remains highly challenging. Unlike in the ultraviolet or visible spectral regions {few materials possess direct electronic transitions}} in the mid-infrared and most that do are created through complex band-engineering schemes. An alternative mechanism, independent of dipole active material transitions, relies instead on energy lost to the polar lattice through the Coulomb interaction. Longitudinal phonons radiated in this way can be spectrally tuned through the engineering of polar nanostructures and coupled to localized optical modes in the material, allowing them to radiate mid-infrared photons into the far-field. A recent theoretical work explored this process providing for the first time an indication of its technological relevance when compared to standard thermal emitters. In order to do so it nevertheless used an equilibrium model of the electron gas, making this model difficult to inform the design of an optimal device to experimentally observe the effect. The present paper removes this limitation, describing the electron gas using a rigorous, self-consistent, non-equilibrium Green’s function model, accounting for variations in material properties across the device, and electron-electron interactions. Although the instability of the Schrodinger-Poisson iteration limits our studies to the low-bias regime, our results demonstrate emission rates comparable to that of room-temperature thermal emission despite such low biases. These results provide a pathway to design a confirmatory experiment of this new emission channel, that could power a new generation of mid-infrared optoelectronic devices
Theoretical investigation of phonon polaritons in SiC micropillar resonators
Full text linkOf late there has been a surge of interest in localized phonon polariton resonators which allow for the subdiffraction confinement of light in the midinfrared spectral region by coupling to optical phonons at the surface of polar dielectrics. Resonators are generally etched on deep substrates which support propagative surface phonon polariton resonances. Recent experimental work has shown that understanding the coupling between localized and propagative surface phonon polaritons in these systems is vital to correctly describing the system resonances. In this paper we comprehensively investigate resonators composed of arrays of cylindrical SiC resonators on SiC substrates. Our bottom-up approach, starting from the resonances of single, free-standing cylinders and isolated substrates, and exploiting both numerical and analytical techniques, allows us to develop a consistent understanding of the parameter space of those resonators, putting on firmer ground this blossoming technology
Launching and manipulation of higher-order in-plane hyperbolic phonon polaritons in low-dimensional heterostructures
No full textHyperbolic phonon polaritons (HPhPs) are stimulated by coupling infrared (IR) photons with the polar lattice vibrations. Such HPhPs offer low-loss, highly confined light propagation at subwavelength scales with out-of-plane or in-plane hyperbolic wavefronts. For HPhPs, while a hyperbolic dispersion implies multiple propagating modes with a distribution of wavevectors at a given frequency, so far it has been challenging to experimentally launch and probe the higher-order modes that offer stronger wavelength compression, especially for in-plane HPhPs. In this work, we report the experimental observation of higher-order in-plane HPhP modes stimulated on a 3C-SiC nanowire (NW)/α-MoO3 heterostructure where leveraging both the low-dimensionality and low-loss nature of the polar NWs, higher-order HPhPs modes within two-dimensional α-MoO3 crystal are launched by the one-dimensional 3C-SiC NW. We further study the launching mechanism and determine the requirements for efficiently launching of such higher-order modes. In addition, by altering the geometric orientation between the 3C-SiC NW and α-MoO3 crystal, we demonstrate the manipulation of higher-order HPhP dispersions as a method of tuning. This work illustrates an extremely anisotropic low dimensional heterostructure platform to confine and configure electromagnetic waves at the deep-subwavelength scales for a range of infrared applications including sensing, nano-imaging, and on-chip photonics
Second harmonic generation from strongly coupled localized and propagating phonon-polariton modes
No full textWe experimentally investigate second harmonic generation from strongly coupled localized and propagative phonon polariton modes in arrays of silicon carbide nanopillars. Our results clearly demonstrate the hybrid nature of the system's eigenmodes and distinct manifestation of strong coupling in the linear and nonlinear response. While in linear reflectivity the intensity of the two strongly-coupled branches is essentially symmetric and well explained by their respective localized or propagative components, the second harmonic signal presents a strong asymmetry. Analyzing it in detail, we reveal the importance of interference effects between the nonlinear polarization terms originating in the bulk and in the phonon polariton modes
Sub-nanometer thin oxide film sensing with localized surface phonon polaritons
No full textChemical sensing methods based on surface polaritonic resonances stem from their intense near fields and resultant sensitivity to changes in local refractive index. Polar dielectric crystals (e.g. SiC, hBN) support surface phonon polaritons (SPhPs) from the mid-infrared to terahertz range with mode volumes and quality factors exceeding the best case scenario attained by plasmonic counterparts, making them strong candidates for resonant surface-enhanced infrared spectroscopy (SEIRA). We report on the behaviour of SPhP resonances of SiC nanopillars following the incorporation of sub- and nanometric coatings of Al2O3 and ZrO2 obtained by atomic layer deposition. Concurrent anomalous red and blue-shifts of SPhP resonances were observed upon deposition of sub-nanometric Al2O3 films, with shift direction dictated by the mode position relative to the ordinary longitudinal optic (LO) phonon of Al2O3. These concurrent shifts, which are attributed to coupling to the Berreman mode of the Al2O3 layer, persist for thicker films and are correctly predicted by numerical calculations employing the measured Al2O3 permittivity. Deposition of ZrO2, whose phonon resonances are detuned from the SPhPs, also led to anomalous blue-shifts of transverse and longitudinal SPhP resonances around 900 cm-1 for films up to ≈ 1.5 nm, reversing to the canonical red-shift for thicker layers. These anomalous shifts were not reproduced numerically using the measured ZrO2 permittivity and suggest the existence of a localized surface state, which when modelled as a simple Lorentz oscillator, provide semi-quantitative agreement with experimental results. In addition, predicted shifts for thicker ZrO2 layers may thus provide a tool for real-time monitoring of ultrathin film growth
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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