Excitation Polarization Research Articles

Spin polarization of exciton-polariton condensate in a photonic synthetic effective magnetic field

The authors investigate here the spin polarization of localized exciton-polariton condensates in CdTe-based microcavities doped with magnetic ions. They demonstrate that an effective magnetic field originating from the photonic potential landscape leads to the formation of elliptically polarized condensate. The degree of spin polarization of the condensate depends on the excitation power and polarization of the laser. Based on the magnetic field behavior of the condensate in the presence of magnetic ions, they estimate the polariton-polariton interaction strength in a CdTe system.

An Improved Core-Corona Model for Λ and Λ Polarization in Relativistic Heavy-Ion Collisions

Due to its sensitivity to the dynamics of strongly interacting matter subject to extreme conditions, hyperon global polarization has become an important observable to study the system created in relativistic heavy-ion collisions. Recently, the STAR and HADES collaborations have measured the global polarization of both Λ and Λ¯ produced in semi-central collisions in a wide range of collision energies. The polarization excitation functions show an increasing trend as the collision energy decreases, with the increase being more pronounced for the Λ¯. In this work, we make a summary of a core-corona model that we have developed to quantify the global polarization contributions from Λ and Λ¯ created in different regions of the fireball. The core-corona model assumes that Λs and Λ¯s are produced in both regions, the high-density core and the lower density corona, with different relative abundances which modulate the polarization excitation function. We have shown that the model works well for the description of experimental results. The global polarization excitation functions computed with the model show a peak at different collision energies in the region sNN≤10 GeV. Finally, we discuss and report on the model global polarization predictions for BES-II, NICA and CBM at FAIR and HADES energies.

Satellite-transition double cross-polarization HETCOR under fast MAS

Double-cross polarization to the satellite-transitions (STs) of half-integer quadrupolar nuclei is demonstrated using proton-detected heteronuclear correlation (HETCOR) under fast magic-angle spinning (MAS). By placing the rf frequency away from the central-transition (CT) and selective to the STs, average Hamiltonian theory shows a scaled effective rf field with a phase equal to the complex ST spinning sideband being irradiated. Such an effective rf field can excite and spinlock STs but the phase spread usually leads to signal cancellation in one-step excitation or cross polarization experiments. The cancellation does not occur for two-step double cross-polarization (DCP) HETCOR experiments, therefore high efficiencies can be obtained. With careful magic-angle calibration, ST and double-quantum ST (DQST) HETCOR experiments are demonstrated with the 35Cl nuclei in histidine·HCl·H2O. These experiments provide additional information over the commonly observed CT spectra and near isotropic resolution in the case of DQST of spin S = 3/2 quadrupolar nuclei.

Polarization and Torsion Insensitive Fiber Bragg Grating Written in Polarization Maintaining ZEBRA Fiber With Artificial Anisotropy

We present first fiber Bragg grating (FBG) inscribed in polarization maintaining (PM) optical fiber with artificially anisotropic core achieved by an appropriate distribution of discrete germanium-doped areas in nanoscale. We proved that this FBG reveals unique properties. Its single-resonance spectral shape, strain and temperature sensitivities are similar to that for grating written in cylindrically symmetrical optical fiber, which indicates that it behaves as the grating fabricated in a non-PM fiber, whereas it is written in the fiber that preserves the orthogonal polarization components of the mode. Moreover, due to the relatively low birefringence of the fiber, the FBG is insensitive to the excited polarization state and twist, and only a negligible shift of the spectrum is noticeable with no changes in its shape. Thus, FBG inscribed in ZEBRA fiber is a kind of hybrid structure that can be used for all-fiber lasers that generate polarized wave, as well as for polarization fiber sensors and components with spectral insensitivity to random or intentional twist.

Tunable NIR Lasing in MOF for Multi‐Level Complex Photonic Barcodes

AbstractDeveloping functional photonic tags is of great importance to meet the globally increasing demand for information security and anti‐counterfeiting. However, it still suffers from the restricted encoding capacity, low complexity, and unsatisfactory confidentiality. Herein, a strategy is demonstrated to construct multi‐level complex photonic barcodes in near‐infrared (NIR) region based on a composition‐graded metal‐organic framework (MOF) heterostructure with the hierarchical encapsulation of different dye molecules. Such MOF microstructure exhibits switchable dual‐wavelength NIR lasing by adjusting the excited position, polarization direction, and pump energy. Thus, through converting the laser spectra with dynamic and regular changes to solid bars, the multi‐block photonic barcodes with three‐level encoding system are constructed, dramatically increasing the complexity and capacity. It makes the MOF‐based heterostructure with switchable lasing properties become a hard‐to‐counterfeit potential material for advanced anticounterfeiting of high‐level security.

Theoretical investigation of solvent and oxidation/deprotonation effects on the electronic structure of a mononuclear Ru-aqua-polypyridine complex in aqueous solution.

Mononuclear polypyridine ruthenium (Ru) complexes can catalyze various reactions, including water splitting, and can also serve as photosensitizers in solar cells. Despite recent progress in their synthesis, accurately modeling their physicochemical properties, particularly in solution, remains challenging. Herein, we conduct a theoretical investigation of the structural and electronic properties of a mononuclear Ru-aqua polypyridine complex in aqueous solution, considering five of its possible oxidation/protonation states species: [RuII(H2O)(py)(bpy)2]2+, [RuII(OH)(py)(bpy)2]+, [RuIII(H2O)(py)(bpy)2]3+, [RuIII(OH)(py)(bpy)2]2+ and [RuIV(O)(py)(bpy)2]2+, where py = pyridine and bpy = 2,2'-bipyridine. At first, we investigate the impact of proton-coupled and non-coupled electron transfer reactions on the geometry and electronic structure of the complexes in vacuum and in solution, using an implicit solvent model. Then, using a sequential multiscale approach that combines quantum mechanics and molecular mechanics (S-QM/MM), we examine the explicit solvent effects on the electronic excitations of the complexes, and compare them with the experimental results. The complexes were synthesized, and their absorption spectra measured in aqueous solution. To accurately describe the QM interactions between the metal center and the aqueous ligand in the MM simulations, we developed new force field parameters for the Ru atom. We analyze the solvent structure around the complexes and account for its explicit influence on the polarization and electronic excitations of the complexes. Notably, accounting for the explicit solvent polarization effects of the first solvation shells is essential to correctly describe the energy of the electronic transitions, and the explicit treatment of the hydrogen bonds at the QM level in the excitation calculations improves the accuracy of the description of the metal-to-ligand charge-transfer bands. Transition density matrix analysis is used to characterize all electronic transitions in the visible and ultraviolet ranges according to their charge-transfer (CT) character. This study elucidates the electronic structure of those ruthenium polypyridyl complexes in aqueous solution and underscores the importance of precisely describing solvent effects, which can be achieved employing the S-QM/MM method.

Λ and Λ¯ global polarization from the core-corona model

We report on work aimed to describe the Λ and Λ¯ global polarizations in a heavy-ion collision environment using the core-corona model, where the source of these hyperons is a high-density core and a less dense corona. We show that the overall properties of the polarization excitation functions can be linked to the relative abundance of Λs and Λ¯s coming from the core versus those coming from the corona. Both global polarizations peak at collision energies √ sNN . 10 GeV. The exact positions and heights of these peaks depend not only on a reversal of relative abundances with collision energy, but also on the centrality class, both related to the QGP volume and lifetime.

Electric field control of electromagnon frequency in multiferroics

Electromagnons, which are coupled polar and magnetic excitations in magnetoelectric materials, are of large interest for electronic and computing technological devices. Using molecular dynamics simulations based on an ab initio effective Hamiltonian, we predict that the frequency of several electromagnons can be tuned by the application of electric fields in the model multiferroic ${\mathrm{BiFeO}}_{3}$, with this frequency either increasing or decreasing depending on the selected electromagnon. In particular, we show that the frequency of electromagnons localized at ferroelectric domain walls can be tuned over a 200 GHz range by realistic dc electric fields. We interpret the realized frequency increase (decrease) by local hardening (softening) of the associated polar phonons which couples to the applied electric field. The increase versus decrease in the electromagnon frequency is further found to be correlated with the real-space localization of such phonons.

Unveiling room temperature upconversion photoluminescence in monolayer WSe2.

Upconversion photoluminescence (UPL) is a phenomenon describing an anti-Stokes process where the emitted photons have higher energy than the absorbed incident photons. Transition metal dichalcogenides (TMDCs) with strong photon-exciton interactions represent a fascinating platform for studying the anti-Stokes UPL process down to the monolayer thickness limit. Herein, we demonstrate room-temperature UPL emission in monolayer WSe2 with broadband near-infrared excitation. The measured excitation power dependence of UPL intensity at various upconversion energy gains unveils two distinguished upconversion mechanisms, including the one-photon involved multiphonon-assisted UPL process and the two-photon absorption (TPA) induced UPL process. In the phonon-assisted UPL regime, the observed exponential decay of UPL intensity with the increased energy gain is attributed to the decreased phonon population. Furthermore, valley polarization properties of UPL emission with circular polarization excitation is investigated. The demonstrated results will advance future photon upconversion applications based on monolayer TMDCs such as night vision, semiconductor laser cooling, and bioimaging.

Dual-Function Metasurface for Tunable Selective Absorption.

Metamaterials have become a powerful technique in interdisciplinary research, especially in the field of designing terahertz devices. In this paper, two pairs of different structural units of aluminum-polymer composite metamaterials (APCM) for tunable selectivity are designed. One is designed to achieve high-contrast near-field imaging of linear polarized waves, the other is designed to achieve high-contrast near-field imaging of circularly polarized waves, which means the structural units have very large circular dichroisms. After theoretical design and simulation optimization, it can be found that the contrast of near-field imaging can be effectively controlled by using vanadium oxide (VO2) to fill the open gap of the structure. When the conductivity of VO2 is 200 S/m, both the reflection difference under linear polarization excitation and the reflection difference under the excitation of the circularly polarized wave are at the maximum. The former has a modulation depth of 0.8, and the latter has a modulation depth of 0.55. This work shows excellent tunable selective absorption ability, which will promote the application of metamaterials in terahertz absorber, such as biomedical, non-destructive testing, security inspection, wireless communication and so on.

Photoluminescence Polarization of MAPbBr3 Perovskite Nanostructures. Can the Dielectric Contrast Effect Explain It?

The dielectric contrast effect is usually evoked to explain anisotropy of optical properties of elongated nanoobjects, for example, semiconductor nanowires. We applied two-dimensional polarization imaging microscopy to measure the polarization of photoluminescence (PL) excitation and PL intensity of nanoaggregates of in-situ formed MAPbBr3 perovskite nanoparticles in a stretched polymeric matrix. Scanning electron microscopy images of these objects were also acquired to characterize their sizes and shapes. We find that individual perovskite aggregates with sizes of 100–300 nm often possess a PL excitation polarization degree as high as 0.5–0.9, which is up to three times higher than the polarization degree of absorption predicted by the dielectric contrast effect. Small aggregates of nanoparticles possess an emission polarization degree substantially higher than that of excitation. Computer simulations of many possible scenarios show that the dielectric contrast alone cannot quantitatively explain the polarization properties of the studied objects. We propose energy transfer to localized emitting sites and the dependence of PL yield on excitation power density as possible factors strongly influencing the polarization properties of PL emission and PL excitation, respectively.

Structurally engineered colloidal quantum dot phosphor using TiO2 photonic crystal backbone

Photonic crystal (PhC) phosphor, in which the phosphor material is periodically modulated for an enhancement in color-conversion efficiency via resonant absorption of excitation photons, is a paradigm-shifting structural phosphor platform. Two-dimensional (2D) square-lattice PhC phosphor is currently considered the most advanced platform because of not only its high efficiency, but also its immunity to excitation polarization. In the present study, two major modifications are made to further improve the performance of the 2D PhC phosphor: increasing the refractive index contrast and planarizing the surface. The index contrast is improved by replacing the PhC backbone material with TiO2 whereas the surface planarization is achieved by removing excessive colloidal quantum dots from the surface. In comparison with the reference phosphor, the upgraded PhC phosphor exhibits ~59 times enhanced absorption (in simulations) and ~7 times enhanced emission (in experiments), both of which are unprecedentedly high. Our results not only brighten the viability and applicability of the PhC phosphor but also spur the phosphor development through structural engineering of phosphor materials.

Revealing the nanogeometry of WS2 nanoflowers by polarization-resolved Raman spectroscopy

Recent studies of transition metal dichalcogenides (TMDs) have revealed exciting optical properties, such as stable excitons and chiral light–matter interactions. Chemical vapor deposition techniques provide a platform for the fabrication of nanostructures with diverse geometries, ranging from horizontal flakes to flower-like structures. Raman spectroscopy is commonly used to characterize TMDs and their properties. Here, we use polarization-resolved Raman spectroscopy to probe the nanogeometry and orientation of WS2 nanoflower petals. Exciting the nanoflowers with linearly polarized light, we observe an enhanced Raman response from flower petals oriented along the excitation polarization direction. Furthermore, the helicity-resolved Raman response of vertically oriented wall-like flower petals exhibits clear differences with horizontally oriented flakes. Although the photoluminescence from the nanoflowers is strongly reduced, the Raman response upon excitation in resonance with the WS2 excitonic transition does reveal the presence of the exciton, which results in a distinct temperature dependence of the Raman response.

Plasmonic metasurface created by a grating of two-dimensional electron strips on a substrate

We report on the terahertz measurements of a GaAs membrane with a grating of strips formed lithographically in a two-dimensional high-mobility electron system. The designed metasurface demonstrates a highly anisotropic response. For the incident radiation polarization along the strips, a plasma edge is present in the transmission through the structure. Its frequency can be controlled by engineering the geometrical parameters of the metasurface. When the excitation polarization is perpendicular to the strips, no plasmonic response is observed apart from the transmission governed by the Fabry-P\'erot function.

Carbon Nanotubes Coupled with Silica Toroid Microcavities as Emitters for Silicon-Integrated Photonics

A light source based on single-walled carbon nanotubes (SWNTs) is one of the promising candidates for a microsized light source on a silicon chip at telecommunication wavelengths in optical communications and optical interconnects. However, SWNT-based light emitters possess the disadvantage of having a very broad emission spectrum. Here, we present an ultranarrow-linewidth photoluminescence (PL) emitter based on a silica toroid resonator, along with SWNTs, on a silicon chip. We simultaneously managed both excitation and emission lights at telecommunication wavelengths on a silicon chip by employing a very simple in-line configuration consisting of a toroid resonator and a tapered fiber for light input and output. Owing to the extremely high Q factor of our silica toroid resonator, we obtained an ultrahigh Q factor (∼2.1 × 104) of C-band PL emission. We also demonstrated strong PL emission under laterally polarized excitation conditions owing to the strong coupling to the toroid resonator, and laterally polarized PL emission can be selectively generated independently of the excitation polarization direction. This SWNT-based PL emitter based on a simple system with a silica toroid resonator can open routes to highly integrated photonics and optoelectronics on silicon-based platforms.

Far‐Field Polarization Engineering from Nonlinear Nanoresonators

AbstractNanoresonators fabricated from low‐loss dielectrics with second‐order nonlinearity have emerged as a widespread platform for nonlinear frequency conversion at the nanoscale. However, a persisting challenge in this research is the generated complex far‐field polarization state of the upconverted light, which is a limiting factor in many applications. It will be highly desirable to generate uniform far‐field polarization states across all propagation directions, to control the polarization truly along the optical axis and to simultaneously be able to tune the polarization along the entire circumference of the Poincaré sphere by solely modifying the excitation polarization. Here, a nonlinear nanoresonator combining all these properties is theoretically proposed and experimentally demonstrated. At first, an analytical model connecting the induced multipolar content of a nanoresonator with a desired far‐field polarization is derived. Based on this, a nonlinear dielectric nanoresonator is designed to enable sum‐frequency generation (SFG) with highly pure and tuneable far‐field polarization states. In the experiment, the nanoresonators fabricated from the III‐V semiconductor gallium arsenide in (110)‐orientation are excited in an SFG scheme with individually controllable excitation beams. The generation of highly uniform and tuneable far‐field polarization states is demonstrated by combining back‐focal plane measurements with Stokes polarimetry.

A new design of a printed reconfigurable coplanar multiband antenna

The demand for multi-functional components has increased enormously in recent years. Advances in integrated technology have enabled researchers to adapt diverse applications operating at different frequencies in a single wireless device. A compact broadband coplanar waveguide (CPW)-fed square aperture monopole antenna with inverted-L grounded strips is first described. The proposed antenna has a small size of 60×60×0.74 mm3 and has excellent performances which include a good input impedance matching with a much wider operating bandwidth, an excitation of the circular polarization at 2.45 GHz, and a stable omnidirectional radiation pattern. Then, a multiband reconfigurable antenna design is developed from this structure. The frequency reconfigurable approach is obtained using a varactor diode. In this work, it is observed that frequency diversity can be obtained by varying the value of the capacity by leaving the dimensions antenna unchanged. The results are given using CST microwave studio and show good performances in terms of return loss, bandwidth, gain and radiation pattern and demonstrate that the proposed antenna offers a reconfigurable solution for multi-standard wireless communication applications.

Polarized Photoluminescence Enhancement of Monolayer MoS2 Coupled with Plasmonic Salisbury‐Type Absorber (Laser Photonics Rev. 16(10)/2022)

Photoluminescence Enhancement In article number 2200008, Wei Li, Ming Xin, Baoli Liu, and colleagues employ the metal-insulator-metal (MIM) Salisbury-type perfect absorber with a symmetry-breaking metallic metasurface to construct an exciton–plasmon coupling system. Fully utilizing the unique property of maximum in-plane electric field of the Salisbury-type absorber in a designed direction, large photoluminescence enhancement and the high degree of linear polarization of photoluminescence independent of the excitation polarization are achieved in monolayer MoS2.

An analysis of the shadow effect for the short-offset transient electromagnetic method

The electromagnetic methods based on long-wire sources, whether in the time or frequency domain, are mainly detected in the far-source zone. Because the observation array is far away from the transmitting source, the amplitude and bandwidth of the signal have a large loss, which limits the detection depth and accuracy of these methods. In the near-source zone, the loss of signal amplitude and bandwidth is relatively small, conducive to improving the detection performance. However, the complex excitation field in the near-source zone makes the observation seriously affected by the source effect. This paper mainly researched the influence of the shadow effect (one of the source effects) on the observation of the short-offset transient electromagnetic method (SOTEM), which is a near-source time-domain method. The results show that the shadow effect has relatively limited influence only on the specific observation channels of the time series of observation data. Based on this, the research on eliminating shadow effects under single / multi-source, multi location and multi polarization excitation modes is carried out. The results show that using a single excitation source with multiple polarization directions or using excitation sources with different polarization directions can improve the detection accuracy of underground targets. All of these lays a foundation for further development of the SOTEM method.

Two-Dimensional Hybrid Perovskitoid Micro/nanosheets: Colorful Ultralong Phosphorescence, Delayed Fluorescence, and Anisotropic Optical Waveguide.

Molecular persistent luminescence, such as room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF), have attracted broad attention in the fields of biological imaging, information security, and optoelectronic devices. However, the development of molecular micro/nanostructures combining both RTP and TADF properties is still in an early stage. Herein, a new type of organic metal hybrid perovskitoid (OMHP) two-dimensional (2D) microcrystal has been fabricated through a facile solution method. The long-lived TADF-RTP dual emission can be highly tuned by changing the excitation wavelength, temperature, and decayed time. Moreover, the 2D OMHP microsheet exhibits an asymmetric and anisotropic optical waveguide with low optical loss coefficient, together with extremely high linearly polarized fluorescence-phosphorescence emission (anisotropy = 0.96), which is promising for the development of polarization-sensitive luminescent materials. Therefore, this work not only demonstrates new OMHP showing colorful persistent luminescence under different modes (such as excitation wavelength, temperature, polarization, lifetime, and dimension) but also takes advantage of the 2D micro/nanostructure to provide potential applications as optical logic gates and for delicate multiple information encryption.