Fluid jets and polar domains, on the relationship between electromechanical instability and topology in ferroelectric nematic liquid crystal droplets
SOFT MATTER Autore/i: Marni, S.; Caimi, F.; Barboza, R.; Clark, N.; Bellini, T.; Lucchetti, L. Classificazione: 1 Contributo su Rivista Abstract: Ferroelectric nematic liquid crystals are a class of recently discovered fluid materials formed by highly polar molecules that spontaneously align along a common direction, giving rise to a macroscopic polarization P. Since the polarization vector is locally collinear to the optical axis n, the study of the spatial patterns of n enables deducing the structure of P. We have carried on such topological study on ferroelectric nematic droplets confined between two solid ferroelectric substrates both when the droplet is in equilibrium and during a jet-emission phase that takes place when the solid surfaces become sufficiently charged. We find that in equilibrium the droplet splits in striped domains in which P has alternating directions. When these domains extend close to the droplets' perimeter, P adopts a pi-twisted structure to minimize accumulation of polarization charges. As the substrate surface charge is increased above threshold, fluid jets are emitted with a quasi-periodic pattern, a behaviour suggesting that their location is governed by an electrofluidic instability on the droplets' rim, in turn indicating the absence of specific trigger points. Soon after their emission, the jet periodicity is lost; some jets retract while other markedly grow. In this second regime, jets that grow are those that more easily connect to polar domains with P along the jet axis. Occasionally, ejection of isolated spikes also occurs, revealing locations where polarization charges have accumulated because of topological patterns extending on length scales smaller than the typical domain size.Ferroelectric nematic droplets confined between two ferroelectric substrates separated by a thin gap provide easy access to the topology and to its relationship with the electromechanical instability generated by substrates charging. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/332054
2024
Polarization Coupling between Ferroelectric Liquids and Ferroelectric Solids: Effects of the Fringing Field Profile
CRYSTALS Autore/i: Marni, S.; Barboza, R.; Oluwajoba, A. S.; Zamboni, R.; Lucchetti, L. Classificazione: 1 Contributo su Rivista Abstract: Recent experiments devoted to characterizing the behavior of sessile ferroelectric liquid droplets on ferroelectric solid substrates have shown the existence of a droplet electromechanical Rayleigh-like instability. The instability is induced by the bulk polarization of the ferroelectric fluid, which couples to the polarization of the underlying substrate through its fringing field and solid-fluid interface coupling. With the aim of characterizing this phenomenon, namely the coupling between the polarizations of a fluid and a solid material, we studied the behavior of ferroelectric liquid droplets confined between two solid substrates, arranged in different configurations, realized to generate fringing fields with different profiles. The results show that the features of the droplets instability are indeed affected by the specific fringing field shape in a way dominated by the minimization of the electrostatic energy associated with the bulk polarization of the ferroelectric fluid. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/332052
2023
Optical control of mass ejection from ferroelectric liquid droplets: A possible tool for the actuation of complex fluids
JOURNAL OF MOLECULAR LIQUIDS Autore/i: Marni, Stefano; Barboza, Raouf; Zaltron, Annamaria; Lucchetti, Liana Classificazione: 1 Contributo su Rivista Abstract: We report on the optical control of the recently observed electromechanical instability of ferroelectric liquid droplets exposed to the photovoltaic field of a lithium niobate ferroelectric crystal substrate. The ferroelectric liquid is a nematic liquid crystal in which almost complete polar ordering of the molecular dipoles generates an internal macroscopic polarization locally collinear to the mean molecular long axis. Upon entering the ferroelectric phase, droplets irradiated by unfocused beam undergo an electromechanical instability and disintegrate by the explosive emission of fluid jets. We show here that the regions of jets emission can be controlled by focusing the light beam in areas close to the droplet's edge. Once emitted, the fluid jets can be walked by moving the beam up to millimeter distance from the mother droplet. Reverting the lithium niobate substrate, jets become thinner and show the tendency of being repelled by the beam instead of being attracted, thus offering an additional tool for their optical manipulation. These observations may pave the way to intriguing applications of ferroelectric nematic fluids related to manipulation, actuation, and control of soft, flexible materials. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/318712
2023
On the Behavior of Ferroelectric Liquid Droplets in the Vicinity of a Ferroelectric Solid
CRYSTALS Autore/i: Barboza, Raouf; Bahwi, Sameh; Marni, Stefano; Lucchetti, Liana Classificazione: 1 Contributo su Rivista Abstract: We analyzed the behavior of sessile ferroelectric liquid droplets in the vicinity of a pyroelectrically charged ferroelectric crystal, an experimental configuration that allows testing the recently observed coupling between the polarizations of the fluid and solid materials, in conditions of no direct contact. Results demonstrate that polarizations’ coupling also exists in this configuration and has two distinct effects. Specifically, it gives rise both to an electromechanical instability of the liquid droplets consisting in the sudden ejection of interfacial fluid jets, and to a slow droplet motion toward the ferroelectric solid driven by a dielectrophoretic force. The two effects can possibly be separated, depending on the droplet size. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/315234
2023
Walking Ferroelectric Liquid Droplets with Light
ADVANCED MATERIALS Autore/i: Marni, Stefano; Nava, Giovanni; Barboza, Raouf; Bellini, Tommaso; Lucchetti, Liana Classificazione: 1 Contributo su Rivista Abstract: The motion of ferroelectric liquid sessile droplets deposited on a ferroelectric lithium niobate substrate can be controlled by a light beam of moderate intensity irradiating the substrate at a distance of several droplet diameters from the droplet itself. The ferroelectric liquid is a nematic liquid crystal, in which almost complete polar ordering of the molecular dipoles generates an internal macroscopic polarization locally collinear to the mean molecular long axis. Upon entering the ferroelectric phase, droplets are either attracted toward the center of the beam or repelled, depending on the side of the lithium niobate exposed to light irradiation. Moreover, moving the beam results in walking the ferroelectric droplet over long distances on the substrate. This behavior is understood as due to the coupling between the polarization of the ferroelectric droplet and the polarization photoinduced in the irradiated region of the lithium niobate substrate. Indeed, the effect is not observed in the conventional nematic phase, suggesting the crucial role of the ferroelectric liquid crystal polarization. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/315233
2022
Optical control of light polarization in heliconical cholesteric liquid crystals
OPTICS LETTERS Autore/i: Nava, G; Barboza, R; Simoni, F; Iadlovska, O; Lavrentovich, Od; Lucchetti, L Classificazione: 1 Contributo su Rivista Abstract: We show here that light polarization of a beam propagating through a heliconical cholesteric cell can be controlled by tuning the Bragg resonance of the structure. We demonstrate that this control is achieved by varying either the low-frequency electric field or the intensity of a pump beam impinging on the sample. The study confirms the recently reported phenomenon of optical tuning of the heliconical cholesterics and opens the door for the development of simple and efficient polarization modulators controlled electrically or optically. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/304220
2022
Quantum walks of two correlated photons in a 2D synthetic lattice
NPJ QUANTUM INFORMATION Autore/i: Esposito, C.; Barros, M. R.; Duran Hernandez, A.; Carvacho, G.; Di Colandrea, F.; Barboza, R.; Cardano, F.; Spagnolo, N.; Marrucci, L.; Sciarrino, F. Classificazione: 1 Contributo su Rivista Abstract: Quantum walks represent paradigmatic quantum evolutions, enabling powerful applications in the context of topological physics and quantum computation. They have been implemented in diverse photonic architectures, but the realization of two-particle dynamics on a multidimensional lattice has hitherto been limited to continuous-time evolutions. To fully exploit the computational capabilities of quantum interference it is crucial to develop platforms handling multiple photons that propagate across multidimensional lattices. Here, we report a discrete-time quantum walk of two correlated photons in a two-dimensional lattice, synthetically engineered by manipulating a set of optical modes carrying quantized amounts of transverse momentum. Mode-couplings are introduced via the polarization-controlled diffractive action of thin geometric-phase optical elements. The entire platform is compact, efficient, scalable, and represents a versatile tool to simulate quantum evolutions on complex lattices. We expect that it will have a strong impact on diverse fields such as quantum state engineering, topological quantum photonics, and Boson Sampling. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/298560
2022
Ultra-sensitive measurement of transverse displacements with linear photonic gears
NATURE COMMUNICATIONS Autore/i: Barboza, R.; Babazadeh, A.; Marrucci, L.; Cardano, F.; de Lisio, C.; D'Ambrosio, V. Classificazione: 1 Contributo su Rivista Abstract: Accurately measuring mechanical displacements is essential for a vast portion of current technologies. Several optical techniques accomplish this task, allowing for non-contact sensing even below the diffraction limit. Here we introduce an optical encoding technique, dubbed “linear photonic gears”, that enables ultra-sensitive measurements of a transverse displacement by mapping it into the polarization rotation of a laser beam. In ordinary ambient conditions, we measure the relative shift between two objects with a resolution of 400 pm. We argue that a resolution of 50 pm should be achievable with existing state-of-the-art technologies. Our single-optical-path scheme is intrinsically stable and it could be implemented as a compact sensor, using cost effective integrated optics. We anticipate it may have a strong impact on both research and industry. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/298561
2022
Explosive electrostatic instability of ferroelectric liquid droplets on ferroelectric solid surfaces
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Autore/i: Barboza, R.; Marni, S.; Ciciulla, F.; Ali, MIR FAROOQ; Nava, G.; Caimi, F.; Zaltron, A.; Clark, N. A.; Bellini, T.; Lucchetti, L. Classificazione: 1 Contributo su Rivista Abstract: We investigated the electrostatic behavior of ferroelectric liquid droplets exposed to the pyroelectric field of a lithium niobate ferroelectric crystal substrate. The ferroelectric liquid is a nematic liquid crystal, in which almost complete polar ordering of the molecular dipoles generates an internal macroscopic polarization locally collinear to the mean molecular long axis. Upon entering the ferroelectric phase by reducing the temperature from the nematic phase, the liquid crystal droplets become electromechanically unstable and disintegrate by the explosive emission of fluid jets. These jets are mostly interfacial, spreading out on the substrate surface, and exhibit fractal branching out into smaller streams to eventually disrupt, forming secondary droplets. We understand this behavior as a manifestation of the Rayleigh instability of electrically charged fluid droplets, expected when the electrostatic repulsion exceeds the surface tension of the fluid. In this case, the charges are due to the bulk polarization of the ferroelectric fluid, which couples to the pyroelectric polarization of the underlying lithium niobate substrate through its fringing field and solid-fluid interface coupling. Since the ejection of fluid does not neutralize the droplet surfaces, they can undergo multiple explosive events as the temperature decreases. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/305819
2021
Surface alignment of ferroelectric nematic liquid crystals
SOFT MATTER Autore/i: Caimi, F.; Nava, G.; Barboza, R.; Clark, N. A.; Korblova, E.; Walba, D. M.; Bellini, T.; Lucchetti, L. Classificazione: 1 Contributo su Rivista Abstract: The success of nematic liquid crystals in displays and optical applications is due to the combination of their optical uniaxiality, fluidity, elasticity, responsiveness to electric fields and controllable coupling of the molecular orientation at the interface with solid surfaces. The discovery of a polar nematic phase opens new possibilities for liquid crystal-based applications, but also requires a new study of how this phase couples with surfaces. Here we explore the surface alignment of the ferroelectric nematic phase by testing different rubbed and unrubbed substrates that differ in coupling strength and anchoring orientation and find a variety of behaviors - in terms of nematic orientation, topological defects and electric field response - that are specific to the ferroelectric nematic phase and can be understood as a consequence of the polar symmetry breaking. In particular, we show that by using rubbed polymer surfaces it is easy to produce cells with a planar polar preferential alignment and that cell electrostatics (e.g.grounding the electrodes) has a remarkable effect on the overall homogeneity of the ferroelectric ordering. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/295727
2021
Bloch-Landau-Zener dynamics induced by a synthetic field in a photonic quantum walk
APL PHOTONICS Autore/i: D'Errico, A.; Barboza, R.; Tudor, R.; Dauphin, A.; Massignan, P.; Marrucci, L.; Cardano, F. Classificazione: 1 Contributo su Rivista Abstract: Quantum walks are processes that model dynamics in coherent systems. Their experimental implementations proved to be key to unveiling novel phenomena in Floquet topological insulators. Here, we realize a photonic quantum walk in the presence of a synthetic gauge field, which mimics the action of an electric field on a charged particle. By tuning the energy gaps between the two quasi-energy bands, we investigate intriguing system dynamics characterized by the interplay between Bloch oscillations and Landau-Zener transitions. When both gaps at quasi-energy values of 0 and π are vanishingly small, the Floquet dynamics follows a ballistic spreading. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/300404
2021
Optical force-based detection of splay and twist viscoelasticity of CCN47 across the Nematic-to-Smectic A transition
JOURNAL OF MOLECULAR LIQUIDS Autore/i: Lucchetti, L.; Nava, G.; Barboza, R.; Ciciulla, F.; Bellini, T. Classificazione: 1 Contributo su Rivista Abstract: We measured the splay and twist elastic constant K and viscosity η of CCN47 by coupling optical forces with the nematic director and detecting the resulting deformation. This approach enables to separately induce each of the two distortions and allows to characterize the viscoelastic properties of both the nematic and the smectic A phase. We find that in the nematic phase far from the transition the splay elastic constant K1 is larger than that of twist K2, while its viscosity is smaller, ηsplay < ηtwist. Upon lowering the temperature, K1 and ηsplay continuously increase in the nematic and smectic phase. On the contrary, K2 and ηtwist exhibit an abrupt growth when approaching the N/SmA transition, confirming the expected critical behavior. The twist viscoelastic ratio remains approximately constant in the whole nematic phase, indicating that the critical exponents for K2 and ηtwist are similar. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/295725
2020
Two-dimensional topological quantum walks in the momentum space of structured light
OPTICA Autore/i: D’Errico, Alessio; Cardano, Filippo; Maffei, Maria; Dauphin, Alexandre; Barboza, Raouf; Esposito, Chiara; Piccirillo, Bruno; Lewenstein, Maciej; Massignan, Pietro; Marrucci, Lorenzo Classificazione: 1 Contributo su Rivista Abstract: Quantum walks are powerful tools for quantum applications and for designing topological systems. Although they are simulated in a variety of platforms, genuine two-dimensional realizations are still challenging. Here we present an innovative approach to the photonic simulation of a quantum walk in two dimensions, where walker positions are encoded in the transverse-wavevector component of a single light beam. The desired dynamics is obtained by means of a sequence of liquid-crystal devices, which apply polarization-dependent transverse “kicks” to the photons in the beam. We engineer our quantum walk so that it realizes a periodically driven Chern insulator, and we probe its topological features by detecting the anomalous displacement of the photonic wavepacket under the effect of a constant force. Our compact, versatile platform offers exciting prospects for the photonic simulation of two-dimensional quantum dynamics and topological systems. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/279675
2020
Umbilical defect dynamics in an inhomogeneous nematic liquid crystal layer
PHYSICAL REVIEW. E Autore/i: Zambra, V.; Clerc, M. G.; Barboza, R.; Bortolozzo, U.; Residori, S. Classificazione: 1 Contributo su Rivista Abstract: Electrically driven nematic liquid crystals layers are ideal contexts for studying the interactions of local topological defects, umbilical defects. In homogeneous samples the number of defects is expected to decrease inversely proportional to time as a result of defect-pair interaction law, so-called coarsening process. Experimentally, we characterize the coarsening dynamics in samples containing glass beads as spacers and show that the inclusion of such imperfections changes the exponent of the coarsening law. Moreover, we demonstrate that beads that are slightly deformed alter the surrounding molecular distribution and attract vortices of both topological charges, thus, presenting a mainly quadrupolar behavior. Theoretically, based on a model of vortices diluted in a dipolar medium, a 23 exponent is inferred, which is consistent with the experimental observations. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/290482
2020
Bulk detection of time-dependent topological transitions in quenched chiral models
PHYSICAL REVIEW RESEARCH Autore/i: D'Errico, Alessio; Di Colandrea, Francesco; Barboza, Raouf; Dauphin, Alexandre; Lewenstein, Maciej; Massignan, Pietro; Marrucci, Lorenzo; Cardano, Filippo Classificazione: 1 Contributo su Rivista Abstract: The topology of one-dimensional chiral systems is captured by the winding number of the Hamiltonian eigenstates. Here we show that this invariant can be read out by measuring the mean chiral displacement of a single-particle wave function that is connected to a fully localized one via a unitary and translation-invariant map. Remarkably, this implies that the mean chiral displacement can detect the winding number even when the underlying Hamiltonian is quenched between different topological phases. We confirm experimentally these results in a quantum walk of structured light. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/279775
2019
Topological quantum walks in the two-dimensional space of the transverse momentum of light
Quantum Information and Measurement (QIM) V: Quantum Technologies Autore/i: D’Errico, Alessio; Cardano, Filippo; Maffei, Maria; Dauphin, Alexandre; Barboza, Raouf; Esposito, Chiara; Piccirillo, Bruno; Lewenstein, Maciej; Massignan, Pietro; Marrucci, Lorenzo Classificazione: 4 Contributo in Atti di Convegno (Proceeding) Scheda della pubblicazione:https://iris.univpm.it/handle/11566/279914
2018
Temporal dynamics of light-written waveguides in unbiased liquid crystals
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. B, OPTICAL PHYSICS Autore/i: Alberucci, A.; Barboza, R.; Jisha, C. P.; Nolte, S. Classificazione: 1 Contributo su Rivista Abstract: The control of light by light is one of the main aims in modern photonics. In this context, a fundamental cornerstone is the realization of light-written waveguides in real time, resulting in all-optical reconfigurability of communication networks. Light-written waveguides are often associated with spatial solitons, that is, non-diffracting waves due to a nonlinear self-focusing effect in the harmonic regime. From an applicative point of view, it is important to establish the temporal dynamics for the formation of such light-written guides. Here, we investigate theoretically the temporal dynamics in nematic liquid crystals, a material where spatial solitons can be induced using continuous wave lasers with a few milliwatts of power. We fully address the role of the spatial walk-off and the longitudinal nonlocality in the waveguide formation. We show that for powers large enough to induce light self-steering the beam undergoes several fluctuations before reaching the stationary regime, in turn leading to a much longer formation time for the light-written waveguide. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/278121
2018
Beaming random lasers with soliton control
NATURE COMMUNICATIONS Autore/i: Perumbilavil, S.; Piccardi, A.; Barboza, R.; Buchnev, O.; Kauranen, M.; Strangi, G.; Assanto, G. Classificazione: 1 Contributo su Rivista Abstract: Random lasers are resonator-less light sources where feedback stems from recurrent scattering at the expense of spatial profile and directionality. Suitably-doped nematic liquid crystals can random lase when optically pumped near resonance(s); moreover, through molecular reorientation within the transparency region, they support self-guided optical spatial solitons, i.e., light-induced waveguides. Here, we synergistically combine solitons and collinear pumping in weakly scattering dye-doped nematic liquid crystals, whereby random lasing and self-confinement concur to beaming the emission, with several improved features: all-optical switching driven by a low-power input, laser directionality and smooth output profile with high-conversion efficiency, externally controlled angular steering. Such effects make soliton-assisted random lasers an outstanding route towards application-oriented random lasers. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/278119
2017
Reflective geometric phase in liquid crystal photonics
2017 Conference on Lasers and Electro-Optics Europe European Quantum Electronics Conference (CLEO/Europe-EQEC) Autore/i: Barboza, Raouf; Residori, Stefania; Bortolozzo, Umberto; Clerc, Marcel G. Classificazione: 4 Contributo in Atti di Convegno (Proceeding) Scheda della pubblicazione:https://iris.univpm.it/handle/11566/278126
2016
Berry Phase of Light under Bragg Reflection by Chiral Liquid-Crystal Media
PHYSICAL REVIEW LETTERS Autore/i: Barboza, R.; Bortolozzo, U.; Clerc, M. G.; Residori, S. Classificazione: 1 Contributo su Rivista Abstract: A Berry phase is revealed for circularly polarized light when it is Bragg reflected by a chiral liquid-crystal medium of the same handedness. By using a chiral nematic layer we demonstrate that if the input plane of the layer is rotated with respect to a fixed reference frame, a geometric phase effect occurs for the circularly polarized light reflected by the periodic helical structure of the medium. Theory and numerical simulations are supported by an experimental observation, disclosing novel applications in the field of optical manipulation and fundamental optical phenomena. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/278129
2016
Coarsening dynamics of umbilical defects in inhomogeneous medium
Springer Proceedings in Physics Autore/i: Barboza, R.; Bortolozzo, U.; Clerc, M. G.; Residori, S.; Zambra, V. Editore: Springer Science and Business Media, LLC Classificazione: 4 Contributo in Atti di Convegno (Proceeding) Abstract: Non-equilibrium systems with coexistence of equilibria exhibit a rich and complex defects dynamics in order to reach a more stable configuration. Nematic liquid crystals layer with negative dielectric constant and homeotropic anchoring under the influence of a voltage are the ideal context for studying the interaction of gas of topological vortices. The number of vortices decreases with time. Experimentally, we show that the presence of imperfections drastically changes this coarsening law. Imperfections are achieved by considering glass beads inside the nematic liquid crystal sample. Depending on the disorder of these imperfections, the system exhibits different statistical evolution of the number of umbilical defects. The coarsening dynamics is persistent and is characterized by power laws with different exponents. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/278139
2016
Light-matter interaction induces a shadow vortex
PHYSICAL REVIEW. E Autore/i: Barboza, R.; Bortolozzo, U.; Clerc, M. G.; Davila, J. D.; Kowalczyk, M.; Residori, S.; Vidal-Henriquez, E. Classificazione: 1 Contributo su Rivista Abstract: By sending a light beam on a homeotropic nematic liquid-crystal cell subjected to a voltage with a photosensitive wall, a stable matter vortex can be induced at the center of the beam. When the applied voltage is decreased, the vortex disappears from the illuminated region; however, the system shows a stationary molecular texture. Based on a forced Ginzburg-Landau amplitude equation, we show that the vortex with a core of exponentially suppressed amplitude always remains in a shadow region below instability threshold and that the observed texture is induced by its phase distribution. This is a different type of vortex phase singularity solution. Numerical simulations and experimental observations show a quite fair agreement. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/278130
2015
Programmable lattices of optical vortices in nematic liquid crystal
Proceedings of SPIE - The International Society for Optical Engineering Autore/i: Barboza, R.; Assanto, G.; Bortolozzo, U.; Clerc, M. G.; Residori, S.; Vidal-Henriquez, E. Editore: SPIE Classificazione: 4 Contributo in Atti di Convegno (Proceeding) Abstract: Using self-induced vortex-like defects in the nematic liquid crystal layer of a light valve with photo-sensible wall, we demonstrate the realization of programable optical vortices lattices with arbitrary configuration in space. On each lattice site, every matter vortex acts as a photonic spin-to-orbital momentum coupler and an array of circularly polarized input beams is converted into an output array of vortex beams with topological charges consistent with the vortex matter lattice. The vortex arrangements are explained the basis of light-induced matter defects and topological rules. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/279751
2015
Optical vortex induction via light-matter interaction in liquid-crystal media
ADVANCES IN OPTICS AND PHOTONICS Autore/i: Barboza, R.; Bortolozzo, U.; Clerc, M. G.; Residori, S.; Vidal-Henriquez, E. Classificazione: 1 Contributo su Rivista Abstract: Optical vortices are attracting much attention because of their applications in various fields of optical processing, communications, enhanced imaging systems, and bio-inspired devices. Different methods to generate optical vortices have been devised to date. Among them, several are based on the exploitation of light-matter interaction in liquid-crystal media. This review focuses on the main mechanisms of vortex generation in liquid crystals, in particular on vortex generation induced by umbilics, that is, defects arising in homeotropically aligned nematic cells, which act as topological matter templates able to realize the conversion from spin to orbital angular momentum of an incoming Gaussian beam. Optical vortex induction in a photosensitive light valve is presented as a self-stabilizing mechanism leading to reconfigurable and programmable vortex arrays. On each lattice site, every matter vortex acts as a photonic spin-to-orbital momentum coupler, converting input arrays of circularly polarized beams into output arrays of vortex beams with topological charges consistent with the matter lattice symmetry. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/279749
2014
Light-matter interaction induces a single positive vortex with swirling arms
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY OF LONDON SERIES A: MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES Autore/i: Barboza, R.; Bortolozzo, U.; Clerc, M. G.; Residori, S.; Vidal-Henriquez, E. Classificazione: 1 Contributo su Rivista Abstract: Homeotropic nematic liquid crystal cells with a photosensitive wall and negative dielectric anisotropy exhibit, under the influence of local illumination, stable vortexes with swirling arms that are trapped at the illuminated area. Close to the Fréedericksz transition an amplitude equation is derived, which allows us to understand the origin of the induced vortex and the competition between the illuminating profile and the elastic anisotropy generating the swirling of the arms. Scheda della pubblicazione:https://iris.univpm.it/handle/11566/279764
