Perpendicular Polarization Research Articles

Molecular alignment-assisted spectral broadening and shifting in the near-infrared with a recycled depleted pump from an optical parametric amplifier

We demonstrate how the depleted pump of an optical parametric amplifier can be recycled for impulsive alignment of a molecular gas inside a hollow-core fiber and use such alignment for the broadening and frequency shift of the signal pulse at a center wavelength of ∼1300 nm. Our results combine non-adiabatic molecular alignment, self-phase modulation, and Raman non-linearities. We demonstrate spectral shifts of up to 204 nm and a spectral broadening of more than one octave. We also report on the time delays at which broadening occurs, which do not coincide with any of the molecular rotational constants. Further, we encounter that maximum frequency shifts occur when the signal and pump have perpendicular polarization instead of parallel.

On polarization of Smith-Purcell radiation from a photonic crystal slab

We analyze the polarization of radiation arising during the pass of a relativistic electron over a 2D photonic crystal slab consisting of subwavelength particles arranged at the nodes of a flat rectangular lattice. It is shown that the contribution of the parallel and perpendicular polarizations depends on the direction of propagation of the radiation, the bifurcation of the maxima is due to the contribution of the perpendicular polarization, while the asymmetry of the angular distribution is due to the contribution of the parallel polarization.

Experimental characterization of Spherical Bragg Resonators for electromagnetic emission engineering at microwave frequencies

This work reports experimental investigation and numerical validation of millimeter-sized Spherical Bragg Resonators (SBRs) fabricated using 3D printing technology. The frequency dependencies of the reflection and transmission coefficients were analyzed, and eigenfrequency values were calculated to examine the density of photonic states in air/PLA-polylactide SBRs, showing the appearance of an eigenmode and an increase in the local density of states in the core of a defect cavity. A decay rate enhancement of {sim 10}^{2} was obtained for a dipole placed in the core of the defect SBR. The study also investigated the influence of the source position on the resonator's electromagnetic wave energy. Scattering efficiencies up to order twelve of the multipole electric and magnetic contribution in a 10-layer SBR were calculated to validate the presence of the resonant modes observed in the scattering measurements performed for parallel and perpendicular polarizations. The results demonstrate that SBRs can act as omnidirectional cavities to enhance or inhibit spontaneous emission processes by modifying the density of electromagnetic states compared to free space. This finding highlights the potential of SBRs engineering spontaneous electromagnetic emission processes in various applications, including dielectric nanoantennas, optoelectronics devices, and quantum information across the entire electromagnetic spectrum.

Irida-graphyne: A promising material for optoelectronic applications

Irida-graphyne (IGY), a sheet composed of carbon atoms with sp and sp2 hybridization, is offered and compared to irida-graphene (IG). The electronic structure and optical characteristic of IGY are investigated by density functional theory. The thermal and dynamic stabilities of IGY are confirmed by cohesive energy, ab initio molecular dynamics simulation, and phonon dispersion. The results indicated that IGY is metal and exhibits strong anisotropy photoresponse as well as IG to incident light with parallel and perpendicular polarizations. The high dielectric constants and optical absorption are obtained. As a result, these sheets can be used in energy storage systems, and display broad absorption spectra from infrared to ultraviolet region. The reflection and transmission constates indicated that IG and IGY are transparent, particularly in the high-energy region. Hence, the electronic and optical properties of IG and IGY support the idea that they could be used in next-generation optoelectronic devices.

The Design and Performance Evaluation of a 1550 nm All-Fiber Dual-Polarization Coherent Doppler Lidar for Atmospheric Aerosol Measurements

A 1550 nm all-fiber dual-polarization coherent Doppler lidar (DPCDL) was constructed to measure the depolarization ratio of atmospheric aerosols. In lidar systems, the polarization state of the laser source is typically required to be that of linearly parallel polarization. However, due to the influence of the fiber-optical transmission and the large-mode field output of the telescope, the laser polarization state changes. Hence, a polarizer was mounted to the emitting channel of the telescope to eliminate the depolarization effect. A fiber-optical polarization beam splitter divided the backscattered light into components with parallel and perpendicular polarization. The DPCDL used two coherent channels to receive each of these two polarization components. A calibration procedure was designed for the depolarization ratio to determine the differences in gain and non-responsiveness in the two polarization channels. The calibration factor was found to be 1.13. Additionally, the systematic error and the measured random error of the DPCDL were estimated to evaluate the performance of the system. The DPCDL’s systematic error was found to be about 0.0024, and the standard deviation was lower than 0.0048. The Allan deviations of a 1-min averaging window with a low SNR of 19 dB and a high SNR of 27 dB were 0.0104 and 0.0031, respectively. The random errors at different measured heights were mainly distributed below 0.015. To confirm the authenticity of the atmospheric depolarization ratio measured with the DPCDL, two field observations were conducted with the use of a co-located DPCDL and micro-pulse polarization lidar to perform a comparison. The results showed that the correlation coefficients of the aerosol depolarization ratios were 0.73 and 0.77, respectively. Moreover, the two continuous observations demonstrated the robustness and stability of the DPCDL. The depolarization ratios were detected in different weather conditions.

Three Orthogonal Polarization Distribution Mapping of the Tightly Focused Fields with a Dual‐Mode Waveguide Probe

AbstractStrongly confined electromagnetic (EM) fields generated by tightly focused light beams are applied widely in nano‐optics due to their vectorial characteristics. The inclusion of the longitudinal polarized component plays a crucial role in both the physical characteristics and practical uses of tightly focused vector beams. The acquisition of the distributions of the three orthogonal polarized components of these fields is advantageous for the comprehensive examination of their captivating physical phenomena and possible applications. However, this continues to pose a noteworthy obstacle, especially in the case of the fields that are generated by high numerical aperture objectives. A novel approach is proposed to quantifying the three mutually perpendicular polarizations simultaneously in the focal plane. The method utilizes a dual‐mode waveguide probe that is composed of a dielectric nanoparticle and a metal‐dielectric waveguide. This design allows for the simultaneous support of both transverse electric (TE) and transverse magnetic (TM) modes. Consequently, it enables the polarization recognition of scattering light in k‐space. Importantly, this method effectively eliminates any interference originating from the background light. The work involves an analysis of the theoretical notion of the probe and followed by experimental investigations. This approach holds promise for augmenting optical nanoscopy methodologies and their associated applications.

Polarization enhanced two-photon excited fluorescence contrast by shaped laser pulses using a deformable phase plate.

We utilize spatially and temporally tailored laser pulses for polarization enhanced two-photon excited fluorescence contrasts of dyes. The shaped laser pulses are produced by first passing through a temporal pulse shaper and then through a two-dimensional spatial pulse shaper with deformable phase plates. Different spatial beam profiles are presented that demonstrate the potential of the spatial pulse shaper. Particularly, a polarization enhanced fluorescence contrast between two dyes is reported by utilizing specific phase shaping in perpendicular polarization directions. The tailored laser pulses are further modified by the deformable phase plate, and a polarization increased depth-dependent contrast is achieved. This spatial shaping for all polarization directions demonstrates the advantage of deformable phase plate spatial shapers compared to liquid crystals, where only one polarization direction can spatially be modified. The described polarization contrast method allows for three-dimensional scanning of probes and provides perspectives for biophotonic applications.

Pulse-Induced Dynamics of a Charge-Transfer Complex from First Principles.

The ultrafast dynamics of charge carriers in organic donor-acceptor interfaces are of primary importance to understanding the fundamental properties of these systems. In this work, we focus on a charge-transfer complex formed by quaterthiophene p-doped by tetrafluoro-tetracyanoquinodimethane and investigate electron dynamics and vibronic interactions also at finite temperatures by applying a femtosecond pulse in resonance with the two lowest energy excitations of the system with perpendicular and parallel polarization with respect to the interface. The adopted ab initio formalism based on real-time time-dependent density-functional theory coupled to Ehrenfest dynamics enables monitoring the dynamical charge transfer across the interface and assessing the role played by the nuclear motion. Our results show that the strong intermolecular interactions binding the complex already in the ground state influence the dynamics, too. The analysis of the nuclear motion involved in these processes reveals the participation of different vibrational modes depending on the electronic states stimulated by the resonant pulse. Coupled donor-acceptor modes mostly influence the excited state polarized across the interface, while intramolecular vibrations in the donor molecule dominate the excitation in the orthogonal direction. The results obtained at finite temperatures are overall consistent with this picture, although thermal disorder contributes to slightly decreasing interfacial charge transfer.

Effects of neighboring transitions on electromagnetically induced absorption and transparency in 87Rb atoms with respect to varying hyperfine spacings

Effects of neighboring transitions through Doppler broadening on electromagnetically induced absorption (EIA) and electromagnetically induced transparency (EIT) of the degenerate two-level system at the F g =2→F e =1,2, and 3 transitions of the 87Rb D2 line have been investigated. Two different polarization configurations, such as linear parallel and linear perpendicular polarizations of coupling and probe lasers, have been studied. We study the significant variation of EIT and EIA due to the effect of the neighboring transitions via artificial variation of the hyperfine spacings of the 5P3/2 state. We have a new observation such as EIT instead of EIA due to the neighboring effect, even in the case of closed systems such as F g =2→F e =3 of 87Rb for the linear parallel configuration, for the first time to our best knowledge. The observed spectra match well with theoretically calculated spectra. EIAs for the open F g =2→F e =1 and 2 transitions at the linear perpendicular polarization are observed due to neighboring effects. This system may be applied to optical switching systems for future quantum processing application.

Investigation on elastic, optical and thermoelectric properties of 2D MgX (X= O, S, Se, Te) materials under DFT framework

The first principles study of two-dimensional magnesium (Mg) chalcogenides (X = O, S, Se, Te) in square lattice (s-MgX) and hexagonal phases (h-MgX) is investigated for the first time. Except for h-MgSe and h-MgTe, all the square lattice and hexagonal structures in MgX compounds are dynamically stable, agreeing to phonon dispersion calculations. The electronic band structure and projected density of states of s- and h-MgX materials provided insight into the essence of electronic properties of these compounds. All s- and h-MgX compounds are found to be indirect wide band gap semiconductors, according to calculations using PBE and HSE06 functionals. The effective mass, mobility and relaxation time of electrons and holes carriers from the band structure of s- and h-MgX are examined to acquire a better intuition into these materials. Along the zigzag direction, h-MgTe has a largest mobility as well as relaxation time of 78104.92 cm2 V−1s−1 and 64385.56 fs, respectively in the entire MgX series. Additionally, we examined their mechanical stability through elastic characteristics, and the derived elastic parameters and polar graphs of Young's modulus and Poisson's ratio verifying their mechanical stability. In application of parallel and perpendicular field polarizations, the optical properties of s- and h-MgX are examined. The thermoelectric properties of the complete s- and h-MgX series are examined for the temperature range from 50 K to 800 K. The results of the present study reveal that s-MgO and h-MgS are the better thermoelectric materials in the considered series. Finally, since these compounds are mostly UV-active, they may find useful applications in UV-protectant and UV-photodetectors materials.

Slonczewski-spin-current driven dynamics of 180∘ domain walls in spin valves with interfacial Dzyaloshinskii–Moriya interaction

Steady-flow dynamics of ferromagnetic 180∘ domain walls (180DWs) in long and narrow spin valves (LNSVs) with interfacial Dzyaloshinskii–Moriya interaction (IDMI) under spin currents with Slonczewski factor are examined. Depending on the magnetization orientation of polarizers (pinned layers of LNSVs), dynamics of 180DWs in free layers of LNSVs are subtly manipulated: (i) for parallel polarizers, stronger spin polarization leads to higher Walker limit thus ensures the longevity of faster steady flows. Meantime, IDMI induces both the stable-region flapping and its width enlargement. (ii) For perpendicular polarizers, a wandering of 180DWs between bi- and tri-stability persists with the criticality adjusted by the IDMI. (iii) For planar-transverse polarizers, IDMI makes the stable region of steady flows completely asymmetric and further imparts a high saturation wall velocity under large current density. Under the last two polarizers, the ultrahigh differential mobility of 180DWs survives. The combination of Slonczewski spin current and IDMI provides various possibilities of fine controlling on 180DW dynamics, hence opens avenues for magnetic nanodevices with rich functionality and high robustness.

Excellent optical and thermoelectric features of two-dimensional half-metallic ferromagnet Zn1-x(TM)xO: A first principle investigation

The electronic, magneto-optical, and thermoelectric properties of graphene-like ZnO nanosheets doped with transition-metal TM (= Fe, Co, Ni, or Cu) were analyzed using spin-polarized first-principles computations. When a TM atom substitution with the Zn atom, the resultant material exhibits significant spin-polarization around the Fermi level and displays a half-metallic ferromagnet within the PBEsol-GGA. Doped ZnO nanosheets by Fe-, Co-, Ni-, and Cu-dopants generate the total magnetic moment of 4μB, 3μB, 2μB, and 1μB, respectively, which is produced primarily by the TM-3d atoms. The p-d hybridization explains the ferromagnetic interactions caused by the robust coupling among Co-, Ni-, or Cu-3d and anion O-2p orbitals. We have investigated the optical characteristics of TM-doped ZnO nanosheets in parallel (EǁX) and perpendicular (EǁZ) polarization directions. Our analysis demonstrates that the Zn1-x(TM)xO two-dimensional nanosheets can absorb visible sunlight in the (EǁX) polarization direction comparatively to pristine ZnONS. Along the x-axis, we studied the Seebeck coefficient, electrical, electronic thermal conductivities, and power factor for various temperatures. All the TM-doped ZnO (2D) nanosheets demonstrate superior electrical conductivity and high power factor in n-type doping than in p-type doping. According to these findings, TM-doped ZnO nanosheets could represent the next evolution in Spintronic, photovoltaic cells, and thermoelectric technologies.

The emergence of three-dimensional chiral domain walls in polar vortices.

Chirality or handedness of a material can be used as an order parameter to uncovertheemergent electronic properties for quantum information science. Conventionally, chirality is found in naturally occurring biomolecules and magnetic materials. Chirality can be engineered in a topological polar vortex ferroelectric/dielectric system via atomic-scale symmetry-breaking operations. We use four-dimensional scanning transmission electron microscopy (4D-STEM) to map out thetopology-driven three-dimensional domain walls, where the handedness of two neighbor topological domains change or remain the same. The nature of the domain walls is governed by the interplay ofthe local perpendicular (lateral) and parallel (axial) polarization with respect to the tubular vortex structures. Unique symmetry-breaking operations and the finite nature of domain walls result in a triple pointformation at the junction of chiral and achiral domain walls. The unconventional nature of the domain walls with triple point pairs may result in unique electrostatic and magnetic properties potentially useful for quantum sensing applications.

A novel approach to the design of multi section ultra-wideband Jaumann absorber

A novel ultra-wideband Jaumann absorber design and analytical procedure that greatly enhance the absorption bandwidth and absorptivity level using few dielectric layers are described. The absorptivity bandwidth of the proposed structure is much better than the traditional absorbers. In Jaumann absorbers, determining resistivity of resistive sheets is a complex task and optimization techniques are generally utilized for the solution. The new contribution given in this paper is that the reflected waves from each boundary inside the dielectric layers are eliminated. Therefore, input reflection coefficient is obtained analytically using Binomial expansion without any approximation. Then a binomial matching procedure is applied to obtain the ultra-wideband absorption. Absorption enhancement is achieved by quarter wavelength dielectric slabs, resistive sheets with critical resistivities and a metallic ground plane backed final dielectric layer with high permittivity. Proposed structure is designed for normal illumination. Parallel and perpendicular polarizations are also studied for oblique incidences. Absorptivity and reflectivity variations are presented versus frequency in 0–40 GHz band for the 20 GHz design frequency for several structures. It is shown that choosing three layers backed with a final layer (εrb=20) structure gives absorptivity greater than 90% in a 6.8–33.2 GHz band region with a fractional bandwidth of 132%. CST Microwave Studio and AWR programs are used to prove the correctness of the proposed method. Great consistency is observed and demonstrated in the numerical results section.

Cavity Jahn-Teller polaritons in molecules

We investigate Jahn-Teller (JT) polaritons, which emerge from the interaction of the two normal-incidence electromagnetic modes with perpendicular polarizations in a Fabry-Perot cavity resonator with JT active systems. These JT polaritons are characterized by a mixed $(+/-)$--circular electromagnetic polarization that originates from the molecular JT vibronic coupling of the material subsystem. Consequently, the exchange of photonic and vibronic angular momenta can be very efficient; exciting the cavity-JT system with short, polarized light pulses results in a dynamical and oscillatory response of the polarization in the cavity medium. Due to the photonic-vibronic coupling, we show how the cavity polarization direction becomes frequency dependent and does not necessarily coincide with the polarization direction of the external fields used to drive the system.

Ultralong 100 ns spin relaxation time in graphite at room temperature

Graphite has been intensively studied, yet its electron spins dynamics remains an unresolved problem even 70 years after the first experiments. The central quantities, the longitudinal (T1) and transverse (T2) relaxation times were postulated to be equal, mirroring standard metals, but T1 has never been measured for graphite. Here, based on a detailed band structure calculation including spin-orbit coupling, we predict an unexpected behavior of the relaxation times. We find, based on saturation ESR measurements, that T1 is markedly different from T2. Spins injected with perpendicular polarization with respect to the graphene plane have an extraordinarily long lifetime of 100 ns at room temperature. This is ten times more than in the best graphene samples. The spin diffusion length across graphite planes is thus expected to be ultralong, on the scale of ~ 70 μm, suggesting that thin films of graphite — or multilayer AB graphene stacks — can be excellent platforms for spintronics applications compatible with 2D van der Waals technologies. Finally, we provide a qualitative account of the observed spin relaxation based on the anisotropic spin admixture of the Bloch states in graphite obtained from density functional theory calculations.

Locally monochromatic two-step nonlinear trident process in a plane wave

In many-cycle plane waves at intermediate intensities, the nonlinear trident process can be well-approximated by the two sequential steps of nonlinear Compton scattering of a polarised real photon followed by its transformation into an electron-positron pair via nonlinear Breit-Wheeler pair creation. We investigate this two-step process in the intermediate intensity regime by employing the locally monochromatic approximation for each step and numerically evaluating resulting expressions. When photon polarisation is included, it is found to produce an order 10% decrease in the trident rate: the importance of polarisation increases at lower intensities, and decreases at higher intensities. Its importance persists at higher intensities in a linearly-polarised background, but disappears at high intensities in a circularly-polarised background. If the two steps are made to take place in two linearly-polarised plane wave pulses with perpendicular polarisations, the pair yield can be increased by approximately 30% compared to two plane waves with the same polarisation. It is also shown that harmonic structures in the Compton step can be passed to the pair step if the Compton edge is at an energy of the order of the threshold for linear Breit-Wheeler.

Machine Learning Empowered Magnetic Substrate Coupled Broadband and Miniaturized Frequency Selective Surface

This works offers a polarization-insensitive, wide angular stable, and wideband electromagnetic interference shielding structure using an integration of frequency selective surface (FSS) with magnetic substrates. The equivalent circuit model (ECM) together with the analytical model is derived to figure out the physics of the shielding structure. The overall inductance of the shielding structure is increased using a magnetic ferrite sheet and magnetic silicon rubber sheet as substrates. Further, four different deep neural network configurations are investigated with inverse modeling to predict the shielding structure parameters within a fraction of seconds. The mse between expected and predicted output is only 2.92 × <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$10^{-8}$</tex-math></inline-formula> . The entire X-band is shielded with a minimum 10-dB shielding effectiveness (SE) and with SE of 56 dB at resonance. The FSS unit cell size is only 0.21 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda$</tex-math></inline-formula> × 0.21 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda$</tex-math></inline-formula> . Furthermore, the proposed shielding structure shows stable transmission performance up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$75^{\circ}$</tex-math></inline-formula> angle of incidence for both perpendicular and parallel polarization. Finally, a prototype is fabricated and measured using nondestructive free space measurement. Good agreement among the simulated, ECM, analytical model, and measured results demonstrate the efficacy of the proposed technique for building an effective shielding structure.

Saturated absorption spectrum of cesium micrometric-thin cell with suppressed crossover spectral lines

Micrometric-thin cells (MCs) with alkali vapor atoms have been valuable for research and applications of hyperfine Zeeman splitting and atomic magnetometers under strong magnetic fields. We theoretically and experimentally study the saturated absorption spectra using a 100-μm cesium MC, where the pump and probe beams are linearly polarized with mutually perpendicular polarizations, and the magnetic field is along the pump beam. Because of the distinctive thin chamber of the MC, crossover spectral lines in saturated absorption spectra are largely suppressed leading to clear splittings of hyperfine Zeeman transitions in experiments, and the effect of spatial magnetic field gradient is expected to be reduced. A calculation method is proposed to achieve good agreements between theoretical calculations and experimental results. This method successfully explains the suppression of crossover lines in MCs, as well as the effects of magnetic field direction, propagation and polarization directions of the pump/probe beam on saturated absorption spectrum. The saturated absorption spectrum with suppressed crossover lines is used for laser frequency stabilization, which may provide the potential value of MCs for high spatial resolution strong-field magnetometry with high sensitivity.

High hydrogen production in two-dimensional GaTe/ZnI2 type-II heterostructure for water splitting

In this work, first-principles calculation was used to systematically examine the structural, electronic, and optical properties of the GaTe/ZnI2 heterostructure under the biaxial strain effect. The frequency-dependent phonon dispersion relations and molecular dynamics simulations demonstrated the kinetic and thermodynamic stability of this heterostructure. The results showed that the GaTe/ZnI2 heterostructure possesses an indirect energy band of about 1.768 eV/1.065 eV (HSE06/PBE) and has a type-Ⅱ band structure. In addition, results revealed that the GaTe/ZnI2 heterostructure has suitable band edge positions for redox reactions and could be a great photocatalyst for the splitting of water. Moreover, the optical properties were studied in the context of perpendicular field polarizations. Our calculations showed that this heterostructure has a high absorption coefficient reaching 4.5 × 104 cm−1 at 3.2 eV in visible light with the maximum value in the UV region. Overall, the electronic and optical properties of the heterostructure improved significantly. Our findings indicated that the GaTe/ZnI2 heterostructure can be used not only in photocatalysts but also in the photodetectors, gas sensors, and photovoltaic devices.