Local Polarization States Research Articles

Dynamic tailoring large-area surface plasmon polariton excitation

Abstract We propose and demonstrate a method for dynamically changing the patterning of the surface plasmon polariton (SPP) excitation over a large area under spatially inhomogeneous polarized illumination. By illuminating a 1D gold grating with shallow rectangular grooves with a spatially structured polarization beam of near-infrared light (780 nm), we selectively excited SPPs on an extended area. The parameters used to fabricate the grating coupler, matched the wave vector of the incident light with that of the SPP to achieve an efficient coupling. The incident wave illuminating the grating is a spatially inhomogeneous polarized beam. We designed local polarization states to control the local excitation of the SPP in order to pattern large areas. For real-time local control of the polarization state of the extended incident beam, we used a setup with a spatial light modulator and quarter-wave plate.

Chiral topological light for detection of robust enantiosensitive observables

The topological response of matter to electromagnetic fields is a highly demanded property in materials design and metrology due to its robustness against noise and decoherence, stimulating recent advances in ultrafast photonics. Embedding topological properties into the enantiosensitive optical response of chiral molecules could therefore enhance the efficiency and robustness of chiral optical discrimination. Here we achieve such a topological embedding by introducing the concept of chiral topological light—a light beam which displays chirality locally, with an azimuthal distribution of its handedness described globally by a topological charge. The topological charge is mapped onto the azimuthal intensity modulation of the non-linear optical response, where enantiosensitivity is encoded into its spatial rotation. The spatial rotation is robust against intensity fluctuations and imperfect local polarization states of the driving field. Our theoretical results show that chiral topological light enables detection of percentage-level enantiomeric excesses in randomly oriented mixtures of chiral molecules, opening a way to new, extremely sensitive and robust chiro-optical spectroscopies with attosecond time resolution.

Chromatic aberration measurement of liquid crystal Pancharatnam Berry phase lens by a RGB full-Stokes imaging polarimeter

Pancharatnam Berry (PB) phase optical elements can manipulate local polarization state of light in the cross-sectional plane by addressing an additional PB phase relating to the orientation of the optical axis of the waveplate-like structure. However, chromatic aberration including spectrum-dependent retardation and diffraction efficiency limits their applications in the field of visible broadband imaging and display. In this article, the chromatic aberration of a liquid crystal (LC) PB phase lens was measured by a home-built RGB full-Stokes imaging polarimeter. The chirality conversion efficiency and depolarization at RGB wavelengths can be calculated from the measured Stokes vectors. Our experiments show that even the spectrum-dependent retardation exists, the measured PB phase lens has a uniform and high diffraction efficiency in the visible band. Affected by the local LC molecule, the input polarization of RGB light was rotated in varying degrees, but the focusing or defocusing manipulation to the right- or left-hand circular polarization, originated from the PB phase, results in fixed focal lengths for different colors. Our experiments show that the LC-based PB phase lens is suitable for the visible broadband applications.

Local characterization of the polarization state of 3D electromagnetic fields: an alternative approach

A precise knowledge of the polarization state of light is crucial in technologies that involve the generation and application of structured light fields. The implementation of efficient methods to determine and characterize polarization states is mandatory; more importantly, these structured light fields must be at any spatial location at a low expense. Here, we introduce a new characterization method that relies on a rather convenient description of electric fields without neglecting their 3D nature. This method is particularly suitable for highly focused fields, which exhibit important polarization contributions along their propagation direction in the neighborhood of the focal region; i.e., the contributions out of the planes transverse to the optical axis, conventionally used to specify the polarization state of these fields. As shown, the method allows the extraction of information about the three field components at relatively low computational and experimental costs. Furthermore, it also allows characterization of the polarization state of a field in a rather simple manner. To check the feasibility and reliability of the method, we determined both analytically and experimentally the local polarization states for a series of benchmark input fields with it, finding excellent agreement between the theory and experiment.

Cascaded mode converter for generating high-order Poincaré sphere beams of multiple different orders

Structured light fields, especially high-order Poincaré sphere (HOPS) beams, are attracting increasing attention for their intriguing properties and extensive applications. Here, we demonstrate a cascaded mode converter for generating HOPS beams of different orders. The cascaded mode converter is composed of q-plates and half waveplates, which realize switchable generation of HOPS beams of multiple different orders with reliable performance. Exponential growth of the available number of HOPS beams of different orders is achieved. The local polarization state and the order of the HOPS beams can be used as two degrees of freedom to encode 2 bits of information. The proposed method makes it possible to generate multiple and ultrahigh order Poincaré sphere beams and may have potential application in communication systems.

An inverse Faraday effect generated by linearly polarized light through a plasmonic nano-antenna.

The inverse Faraday effect (IFE) generates magnetic fields by optical excitation only. Since its discovery in the 60s, it was believed that only circular polarizations could magnetize matter by this magneto-optical phenomenon. Here, we demonstrate the generation of an IFE via a linear polarization of light. This new physical concept results from the local manipulation of light by a plasmonic nano-antenna. We demonstrate that a gold nanorod excited by a linear polarization generates non-zero magnetic fields by IFE when the incident polarization of the light is not parallel to the long axis of the rod. We show that this dissymmetry generates hot spots of local non-vanishing spin densities (local elliptical polarization state), introducing the concept of super circular light, allowing this magnetization. Moreover, by varying the angle of the incident linear polarization with respect to the nano-antenna, we demonstrate the on-demand flipping of the magnetic field orientation. Finally, this linear IFE generates a magnetic field 25 times stronger than a gold nanoparticle via a classical IFE. Because of its all-optical character, this light-matter interaction opens the way to ultrafast nanomanipulation of magnetic processes such as domain reversal, skyrmions, circular dichroism, control of the spin, its currents, and waves, among others.

Polarization-Sensitive Patterning of Azopolymer Thin Films Using Multiple Structured Laser Beams

The polarization sensitivity of azopolymers is well known. Therefore, these materials are actively used in many applications of photonics. Recently, the unique possibilities of processing such materials using a structured laser beam were demonstrated, which revealed the key role of the distribution of polarization and the longitudinal component of light in determining the shape of the nano- and microstructures formed on the surfaces of thin azopolymer films. Here, we present numerical and experimental results demonstrating the high polarization sensitivity of thin azopolymer films to the local polarization state of an illuminating structured laser beam consisting of a set of light spots. To form such arrays of spots with a controlled distribution of polarization, different polarization states of laser beams, both homogeneous and locally inhomogeneous, were used. The results obtained show the possibility of implementing a parallel non-uniform patterning of thin azopolymer films depending on the polarization distribution of the illuminating laser beam. We believe that the demonstrated results will not only make it possible to implement the simultaneous detection of local polarization states of complex-shaped light fields but will also be used for the high-performance fabrication of diffractive optical elements and metasurfaces.

Polarization Analysis of Gene Sequence Structures: Mapping of Extreme Local Polarization States

A method for visualization and identification of nucleotide sequences is proposed based on the synthesis of phase screens displaying the structure of the analyzed sequences and reconstruction of binary maps of the extreme values of the local Stokes vector components in the diffraction zone. This diffraction zone is formed due to reading out the phase screen by a coherent collimated beam with two orthogonally polarized (x–y) components. With different phase delays of the x–y components of the readout beam introduced by the phase screen elements, this causes a variety of local polarization states in the diffraction zone. The discrimination level for the local component of the Stokes vector chosen for the binary mapping is established near the extreme value for this component. Computer verification of the proposed method using nucleotide sequences for various strains of the model African swine fewer (ASF) virus as the test objects shows its high efficiency in the detection of differences between two compared sequences corresponding to the same type of infectious agent. Analysis of the model data for the strains under study made it possible to establish a power-law character of correlation coefficients of the synthesized binary distributions of extreme local polarization states depending on the discrimination threshold detuning from the maximum value of the Stokes vector component used for the mapping .

Properties of Na0.5Bi0.5TiO3 Ceramics Modified with Fe and Mn.

Na0.5Bi0.5TiO3 (NBT) and Fe- and Mn-modified NBT (0.5 and 1 mol%) ceramics were synthesized by the solid-state reaction method. The crystal structure, dielectric and thermal properties of these ceramics were measured in both unpoled and poled states. Neither the addition of iron/manganese to NBT nor poling changed the average crystal structure of the material; however, changes were observed in the short-range scale. The changes in shapes of the Bragg peaks and in their 2Θ-position and changes in the Raman spectra indicated a temperature-driven structural evolution similar to that in pure NBT. It was found that both substitutions led to a decrease in the depolarization temperature Td and an increase in the piezoelectric coefficient d33. In addition, applying an electric field reactivated and extended the ferroelectric state to higher temperatures (Td increased). These effects could be the result of: crystal structure disturbance; changes in the density of defects; the appearance of (FeTiˈ-), (Mn′Ti-V••O) and (Mn″Tii-V••O )—microdipoles; improved domain reorientation conditions and instability of the local polarization state due to the introduction of Fe and Mn into the NBT; reinforced polarization/domain ordering; and partial transformation of the rhombohedral regions into tetragonal ones by the electric field, which supports a long-range ferroelectric state. The possible occupancy of A- and/or B-sites by Fe and Mn ions is discussed based on ionic radius/valence/electronegativity principles. The doping of Fe/Mn and E-poling offers an effective way to modify the properties of NBT.

Sustained Exosome-Guided Macrophage Polarization Using Hydrolytically Degradable PEG Hydrogels for Cutaneous Wound Healing: Identification of Key Proteins and MiRNAs, and Sustained Release Formulation.

Macrophages (Mφs) are characterized by remarkable plasticity, an essential component of chronic inflammation. Thus, an appropriate and timely transition from proinflammatory (M1) to anti-inflammatory (M2) Mφs during wound healing is vital to promoting resolution of acute inflammation and enhancing tissue repair. Herein, exosomes derived from M2-Mφs (M2-Exos), which contain putative key regulators driving Mφ polarization, are used as local microenvironmental cues to induce reprogramming of M1-Mφs toward M2-Mφs for effective wound management. As an injectable controlled release depot for exosomes, hydrolytically degradable poly(ethylene glycol) (PEG) hydrogels (Exogels) are designed and employed for encapsulating M2-Exos to maximize their therapeutic effects in cutaneous wound healing. The degradation time of the hydrogels is adjustable from 6 days or up to 27 days by controlling the crosslinking density and tightness. The localization of M2-Exos leads to a successful local transition from M1-Mφs to M2-Mφs within the lesion for more than 6 days, followed by enhanced therapeutic effects including rapid wound closure and increased healing quality in an animal model for cutaneous wound healing. Collectively, the hydrolytically degradable PEG hydrogel-based exosome delivery system may serve as a potential tool in regulating local polarization state of Mφs, which is crucial for tissue homeostasis and wound repair.

Metalens for Generating a Customized Vectorial Focal Curve.

Three-dimensional (3D) light fields with spatially inhomogeneous polarization and intensity distributions play an increasingly important role in photonics due to their peculiar optical features and extra degrees of freedom for carrying information. However, it is very challenging to simultaneously control the intensity profile and polarization profile in an arbitrary manner. Here we experimentally demonstrate a metalens that can focus light into an arbitrarily shaped focal curve with a predefined polarization distribution. The efficacy of this approach is exemplified through the demonstration of focused curves in 3D space ranging from simple shapes such as a circle to topologically nontrivial objects such as a 3D knot with controlled local polarization states. This powerful control of the light field would be technically challenging with their conventional counterparts. Our demonstration may find applications in beam engineering and integration optics.

Stimulated Parametric Down-Conversion with Vector Vortex Beams

A vector vortex beam presents local polarization states that are spatially modulated in the plane transverse to propagation. By employing a two-crystal-sandwich source allowing for nonlinear interactions between input fields of any polarization, we analyze experimentally the process of stimulated parametric down-conversion and observe unique effects when the pump and seed fields are vector vortex beams. We reconstruct the transverse polarization pattern of the generated idler beam by Stokes polarimetry. The experimental results obtained are in good qualitative agreement with theory and exhibit manifold polarization transverse distributions for different combinations of pump and seed vector vortex beams, which may find applications in both classical and quantum optics.

Robust in-plane polarization switching in epitaxial BiFeO3 films

The enrichment domain state and its stability consist an imperative part regarding to the high density non-volatile ferroelectric random access memory (FRAM) devices. In this work, epitaxial BiFeO3 (BFO) thin films were prepared by pulsed-leaser deposition (PLD) technology, and the morphology, local polarization state and piezoelectric response were characterized by scanning probe microscopy (SPM) and piezoresponse force microscopy (PFM). The robust in-plane domain dynamic process is observed under the external electric fields. Furthermore, good retention and repeatability are observed especially under high temperature. The new-developed domain patterns are nearly stable, which is quite different from the existed research. The formation of these domains is probably induced by the combination of built-in electric fields and distribution of tip fields, both of which affect the polarization dynamic process. All the obtained results pave a great way for application corresponding to the FRAM devices especially under high temperature circumstance.

Revealing Antiferroelectric Switching and Ferroelectric Wakeup in Hafnia by Advanced Piezoresponse Force Microscopy.

Hafnium oxide (HfO2)-based ferroelectrics offer remarkable promise for memory and logic devices in view of their compatibility with traditional silicon complementary metal oxide semiconductor (CMOS) technology, high switchable polarization, good endurance, and thickness scalability. These factors have led to a steep rise in the level of research on HfO2 over the past number of years. While measurements on capacitors are promising for understanding macroscopic effects, many open questions regarding the emergence of ferroelectricity and electric field cycling behaviors remain. Continued progress requires information regarding the nanoscale ferroelectric behaviors on the bare surface (i.e., without encapsulation), which is notably absent. To overcome this barrier, we have applied complementary modes of piezoresponse force microscopy with the goal of directly and quantitatively sensing nanoscale ferroelectric behaviors in bare HfO2 thin films. Our results on 8 nm Si-doped HfO2 reveal nanoscale domains of local remnant polarization states exhibiting a weak piezoelectric coupling (deff) in the range 0.6-1.5 pm/V. While we observed localized enhancement of deff during progressive stressing of the bare HfO2 thin film, we did not detect stable polarization switching which is a prerequisite of ferroelectric switching. This result could be explained using polarization switching spectroscopy which revealed antiferroelectric-like switching in the form of pinched hysteresis loops as well as increasing remnant response with repeated cycling. As such, our results offer a promising route for material scientists who want to explore the nanoscale origins of antiferroelectricity and ferroelectric wakeup in HfO2.

A pure longitudinal magnetization induced by 4π tightly focusing of two linearly polarized vortex beams

In this paper, according to the inverse Faraday effect, a pure longitudinal magnetization field induced by 4π tightly focusing of two linearly polarized vortex beams (LPVBs) is investigated. We find that the orbital angular momentum (OAM) of these two LPVBs could be transformed into spin angular momentum in the tightly focusing condition, and a longitudinal magnetization with purity of 100% is generated, if the topological charges of the two counterpropagating LPVBs are two identical odd numbers. In addition, the distribution and strength of induced longitudinal magnetization could be regulated by turning the OAM of the two counterpropagating LPVBs and numerical aperture of the two focal lenses, respectively. Besides, the local polarization states of the light field and a three-dimensional magnetization array in the focal region is surveyed. We believe that this 4π setup of generating a pure longitudinal magnetization could potentially be used to the field of storage technology especially for the using of massively parallelized all-optical magnetic recording.

Using the Belinfante momentum to retrieve the polarization state of light inside waveguides

Current day high speed optical communication systems employ photonic circuits using platforms such as silicon photonics. In these systems, the polarization state of light drifts due to effects such as polarization mode dispersion and nonlinear phenomena generated by photonic circuit building blocks. As the complexity, the number, and the variety of these building blocks grows, the demand increases for an in-situ polarization determination strategy. Here, we show that the transfer of the Belinfante momentum to particles in the evanescent field of waveguides depends in a non-trivial way on the polarization state of light within that waveguide. Surprisingly, we find that the maxima and minima of the lateral force are not produced with circularly polarized light, corresponding to the north and south poles of the Poincaré sphere. Instead, the maxima are shifted along the great circle of the sphere due to the phase differences between the scattered TE and TM components of light. This effect allows for an unambiguous reconstruction of the local polarization state of light inside a waveguide. Importantly, this technique depends on interaction with only the evanescent tails of the fields, allowing for a minimally invasive method to probe the polarization within a photonic chip.

Moiré Polarization Interference Photolithography Based on AZO Molecular Glass Pillar Array for Hierarchical Surface Patterning

AbstractA new method termed moiré polarization interference photolithography is developed by using a photoresponsive AZO molecular glass (IAC‐2) for fabricating hierarchical surface patterns. Arrays of hexagonally arranged submicron‐sized pillars are prepared from IAC‐2 by soft‐lithographic hot embossing. For the interference photolithography, the pillar arrays are sequentially exposed to polarization‐type interference fringes formed by the superposition of two laser beams with right‐circular polarization and left‐circular polarization. By rotating the pillar arrays by a predetermined angle around the surface normal after each exposure, moiré patterns are fabricated by deformations of the pillars in response to the local polarization states of the superimposed interference fringes. The fabricated hierarchical surface patterns show features combining the complex mass transfer following the local electric vibration directions of the light wave and the long‐range order generated by the moiré effect. By increasing the exposure time, patterns with growing complexity are formed through partial merging of the pillars. The material and methodology reported here extend typical interference photolithography from light intensity modulation to a new dimension, including the polarization interference of coherent light. This new approach can provide a powerful platform for the fabrication of various complex surface patterns that are unattainable by conventional methods.

Gouy phase effects on propagation of pure and hybrid vector beams.

The robustness of the polarization spatial distribution of vector beams upon propagation is crucial for a number of applications, including optical communications and materials processing. This study has been commonly centered on Gouy phase effects on focused vector beams. In this work, we present a theoretical and experimental analysis of the Gouy phase's effects on the propagation of pure and hybrid vector beams. Experimental results at various axial planes, before and past the focus, are obtained by using a simplified liquid-crystal spatial light modulator-based optical system that allows the easy generation of these beams. Furthermore, a new alternative optical set-up that is devoid of moving elements is demonstrated, which simplifies this study. We experimentally verify the differences between pure and hybrid vector beams upon propagation. While the first ones remain stable, hybrid vector beams show Gouy phase effects that demonstrate an optical activity where the local polarization states rotate by an angle that depends on the propagation distance. Experimental results agree with the theory.

Orbit-induced localized spin angular momentum in the tight focusing of linearly polarized vortex beams.

Optical spin-orbit interaction has gained much interest recently due to its universality and importance in modern photonics. In this Letter, we theoretically demonstrate that orbit-induced localized spin angular momentum (SAM) conversion can occur in the tight focusing of spin-free linearly polarized vortex beams (LPVBs). By analysis of the polarization states that are associated with the SAM density, we attribute the occurrence of such a conversion to the helical-phase-induced change of local polarization states in the focused field. In the local SAM, density can be further regulated by altering the sign and value of the orbital angular momentum in the incident LPVBs, as well as their polarization orientations. This Letter is expected to advance our understanding of optical spin-orbit coupling and benefit applications of optical microscopy and trapping.

Electromechanical control of polarization vortex ordering in an interacting ferroelectric-dielectric composite dimer

Using a free-energy based computational model, we have investigated the response of a system comprising two interacting ferroelectric nanospheres, embedded in a dielectric medium, to a static external electric field. The system response is hysteretic and tunable by changing the inter-particle distance and the orientation of the applied field, which strongly modulates the field-driven long-range elastic interactions between the particles that propagate through the dielectric matrix. At small separations, the sensitivity of the system behavior with respect to the electric field direction originates from drastically different configurations of the local vortex-like polarization states in ferroelectric particles. This suggests new routes for the design of composite metamaterials whose dielectric properties can be controlled and tuned by selecting the mutual arrangement of their ferroelectric components.