Perpendicular Polarization Research Articles

Stabilizing current-driven steady flows of 180∘ domain walls in spin valves by interfacial Dzyaloshinskii-Moriya interaction

Effects of interfacial Dzyaloshinskii-Moriya interaction (IDMI) on current-driven dynamics of ${180}^{\ensuremath{\circ}}$ domain walls (180DWs) in long and narrow spin valves (LNSVs) with heavy-metal cap layers are investigated. We focus on LNSVs with in-plane magnetic anisotropy in their free layers. For planar-transverse polarizers (pinned layers of LNSVs), the Walker breakdown is postponed considerably (practical infinity) by IDMI. More interestingly, the originally unstable traveling mode is stabilized by IDMI regardless of the polarization magnitude while bearing a high saturated velocity and thus can serve as a fast carrier of information. For parallel polarizers, the Walker limit is increased, and the corresponding modifications of IDMI to wall velocity in both steady and precessional flows of 180DWs are provided. As for perpendicular polarizers, precessional flow of 180DWs is absent due to the stability of the stationary mode beyond the modified Walker limit. Similar results are obtained for LNSVs with perpendicular magnetic anisotropy in their free layers. Our findings open possibilities for developing magnetic nanodevices based on 180DW propagation with low energy consumption and high robustness.

Rank-Full Arrays for 1-D Mirrored Aperture Synthesis

The antenna array arrangement determines the rank of the transformation matrix in 1-D mirrored aperture synthesis (1-D MAS). Only when the transformation matrix is of full rank can cosine visibilities be precisely solved from the transformation equations. However, the existing literature states that full rank cannot be realized with the default perpendicular polarization of antennas. In this letter, the transformation matrices of arrays with various polarizations of antennas are discussed, and a type of full array with a full-rank transformation matrix is found. Based on these results, the existence conditions for an array with a full-rank transformation matrix are obtained. In addition, a search algorithm with a shorter search time than the existing algorithm is designed to find low-redundancy arrays with a full-rank transformation matrix. The simulations verify that cosine visibilities are precisely solved from the transformation equations for the array with a full-rank transformation matrix.

An ultrafast vibrational study of dynamical heterogeneity in the protic ionic liquid ethyl-ammonium nitrate. I. Room temperature dynamics.

Using ultrafast two-dimensional infrared spectroscopy (2D-IR), a vibrational probe (thiocyanate, SCN-) was used to investigate the hydrogen bonding network of the protic ionic liquid ethyl-ammonium nitrate (EAN) in comparison to H2O. The 2D-IR experiments were performed in both parallel (⟨ZZZZ⟩) and perpendicular (⟨ZZXX⟩) polarizations at room temperature. In EAN, the non-Gaussian lineshape in the FTIR spectrum of SCN- suggests two sub-ensembles. Vibrational relaxation rates extracted from the 2D-IR spectra provide evidence of the dynamical differences between the two sub-ensembles. We support the interpretation of two sub-ensembles with response function simulations of two overlapping bands with different vibrational relaxation rates and, otherwise, similar dynamics. The measured rates for spectral diffusion depend on polarization, indicating reorientation-induced spectral diffusion (RISD). A model of restricted molecular rotation (wobbling in a cone) fully describes the observed spectral diffusion in EAN. In H2O, both RISD and structural spectral diffusion contribute with similar timescales. This complete characterization of the dynamics at room temperature provides the basis for the temperature-dependent measurements in Paper II of this series.

The cross-polarization scattering system for the magnetic fluctuation measurement in the Experimental Advanced Superconducting Tokamak.

The cross-polarization scattering (CPS) system for magnetic fluctuation measurements in the Experimental Advanced Superconducting Tokamak (EAST) has been designed and installed. Different from the Doppler reflectometer (DR) system, the CPS system detects the perpendicular polarization of the electromagnetic wave induced by magnetic fluctuations B̃. The CPS system in the EAST has been developed from the existing Doppler reflectometer system, and they are integrated together for simultaneous measurement of magnetic and density fluctuations. Ray-tracing simulations are used to calculate the scattering locations and the wavenumber coverage of the magnetic fluctuation for CPS. In the experiments, the CPS and DR system data were different in Doppler shift, amplitude, and spectrum broadening. In this article, the hardware design, the ray tracing, and the preliminary results of the system in the EAST are presented.

Interplays of electron and nuclear motions along CO dissociation trajectory in myoglobin revealed by ultrafast X-rays and quantum dynamics calculations

Ultrafast structural dynamics with different spatial and temporal scales were investigated during photodissociation of carbon monoxide (CO) from iron(II)-heme in bovine myoglobin during the first 3 ps following laser excitation. We used simultaneous X-ray transient absorption (XTA) spectroscopy and X-ray transient solution scattering (XSS) at an X-ray free electron laser source with a time resolution of 80 fs. Kinetic traces at different characteristic X-ray energies were collected to give a global picture of the multistep pathway in the photodissociation of CO from heme. In order to extract the reaction coordinates along different directions of the CO departure, XTA data were collected with parallel and perpendicular relative polarizations of the laser pump and X-ray probe pulse to isolate the contributions of electronic spin state transition, bond breaking, and heme macrocycle nuclear relaxation. The time evolution of the iron K-edge X-ray absorption near edge structure (XANES) features along the two major photochemical reaction coordinates, i.e., the iron(II)-CO bond elongation and the heme macrocycle doming relaxation were modeled by time-dependent density functional theory calculations. Combined results from the experiments and computations reveal insight into interplays between the nuclear and electronic structural dynamics along the CO photodissociation trajectory. Time-resolved small-angle X-ray scattering data during the same process are also simultaneously collected, which show that the local CO dissociation causes a protein quake propagating on different spatial and temporal scales. These studies are important for understanding gas transport and protein deligation processes and shed light on the interplay of active site conformational changes and large-scale protein reorganization.

Natural Mode Series Expansion of Transient Transmission Field Through an N-Layer Structure

Time-domain (early- and late-time) transmission response of an $N$ -layer composite structure has been analytically investigated using contour integration for uniform plane waves with perpendicular and parallel polarizations. It has been shown that whereas the late-time transmission response of an $N$ -layer structure is a sum of damped sinusoids provided that it is terminated in a lossless medium (e.g., air medium), its early-time response can be represented as the summation of individual subregional responses, which can be expressed by natural series if any subregion is surrounded by lossless media (assuming that the last layer is lossless). Numerical examples are presented to investigate the early- and late-time transmission responses, and thus validate the results obtained from contour integration, of transparent $N$ -layer composite structures for perpendicular and parallel polarization cases.

Coherent control of optical phonons in GaAs by relative-phase-locked optical pulses under perpendicularly polarized conditions

Coherent control of the optical phonons in GaAs is realized via paired femtosecond pulses that are relative phase-locked and have perpendicular polarizations. To investigate polarization effects, only phonon interference occurs, which contrasts previous experiments with parallel-polarized pulses, which produced as well electronic interference. The results suggest that for an n-GaAs(001) sample the diagonal components of the Raman tensor determinate in the generation of coherent longitudinal optical phonons.

Measurement and assignment of double-resonance transitions to the 8900–9100- cm−1 levels of methane

Optical-optical double-resonance spectroscopy with a continuous wave pump and frequency comb probe allows measurement of sub-Doppler transitions to highly excited molecular states over a wide spectral range with high frequency accuracy. We report on assessment and characterization of sub-Doppler double-resonance transitions in methane measured using a 3.3-$\ensuremath{\mu}\mathrm{m}$ continuous wave optical parametric oscillator as a pump and a 1.67-$\ensuremath{\mu}\mathrm{m}$ frequency comb as a probe. The comb spectra were recorded using a Fourier transform spectrometer with comb-mode-limited resolution. With the pump tuned to nine different transitions in the ${\ensuremath{\nu}}_{3}$ fundamental band, we detected 36 ladder-type transitions to the $3{\ensuremath{\nu}}_{3}$ overtone band region, and 18 V-type transitions to the $2{\ensuremath{\nu}}_{3}$ overtone band. We describe in detail the experimental approach and the pump stabilization scheme, which currently limits the frequency accuracy of the measurement. We present the data analysis procedure used to extract the frequencies and intensities of the probe transitions for parallel and perpendicular relative pump-probe polarization. We compare the center frequencies and relative intensities of the ladder-type transitions to theoretical predictions from the TheoReTS and ExoMol line lists, demonstrating good agreement with TheoReTS.

Observing Tyrosine Kinase Function by Polarization Resolved Fluorescence Microscopy

Receptor tyrosine kinases are membrane proteins crucial for cell signaling processes. Using techniques of molecular biology, we are trying to develop fluorescently labeled receptor kinases molecules that would allow observations of receptor kinase activation by two-photon polarization microscopy (2PPM). 2PPM is an advanced optical microscopy technique developed by our laboratory that allows observing changes in orientation of fluorescent labels attached to membrane proteins, such as due to conformational changes in the membrane proteins. 2PPM works by analyzing fluorescence images acquired with two perpendicular linear polarizations of the excitation light. Differences between the two images can be used to gain insights into the orientation of the observed fluorescent label, and hence into the conformation of the labeled protein. We have now applied the technique to several tyrosine kinase constructs prepared by other laboratories, as well as to constructs we prepared ourselves. We are now in the process of modifying existing constructs in order to be able to visualize activation of several tyrosine kinase receptors important in disease (such as the insulin receptor in diabetes) and in drug discovery. The poster summarizes our progress and current results.

Oblate electron holes are not attributable to anisotropic shielding

The influence of shielding mechanisms on the ratio of perpendicular to parallel scale lengths of multidimensional plasma electron hole equilibria is analyzed theoretically and computationally. It is shown that the “gyrokinetic” model, invoking perpendicular polarization, is based on a misunderstanding and cannot explain the observational trend that greater transverse extent accompanies a lower magnetic field. Instead, the potential in the wings of the hole, outside the region of trapped-electron depletion, has isotropic shielding giving ϕ∝e−r/L/r, with the shielding length L equal to the Debye length for holes much slower than the electron thermal speed. Particle in cell simulations confirm the analysis. Trapped electron charge distribution anisotropy must, therefore, instead underlie the oblate shape of electron holes.

Comparison of mechanical, optical and electronic transport properties of ‎isotropic and anisotropic borophosphene

In this research, mechanical, optical and electronic transport properties of two phases of graphene-like borophosphene are investigated using density functional theory. Graphene-like borophosphene, a honeycomb structure with equal ratio of boron and phosphorus atoms, is introduced in two isotropic and anisotropic phases. For this purpose, band structure, partial density of states, Young’s modulus, Poisson ratios, dielectric function, and current-voltage characteristics are calculated and compared. The results show that the anisotropic phase of graphene-like borophosphene is semimetal and the isotropic phase is a semiconductor with a direct energy gap of 0.9 eV. Moreover, the Young’s modulus has the highest values for both phases in the zigzag and armchair directions of crystal, and the Poisson ratio has the lowest values in these two directions. Besides, optical properties of these two structures include electron energy loss spectroscopy, refractive index, extinction coefficient, optical conductivity and reflection coefficient for parallel and perpendicular polarization of electric fields respect to the sheets are computed by real and imaginary parts of dielectric function using random phase approximation. Plasmon’s energies are obtained 2.24 and 8.88 eV in the armchair direction and 9.01 eV in the zigzag direction for the anisotropic phase and for the isotropic phase, 3.38 and 9.12 eV are obtained in both directions. Both phases are transparent respect to visible light polarized in the perpendicular direction to the crystal, and the reflection and absorption are zero. Due to the selective transmission / absorption / reflection of the electromagnetic wave in the crystals, this material is suggested as a suitable candidate in the fabrication of nano optoelectronic devices. Furthermore, Ohmic behavior is observed in current-voltage characteristics of the isotropic phase after the threshold bias voltage of 0.9 V. As a result of the high Fermi velocity of charge carriers in the anisotropic phase of borophosphene ( ), this material can be used in nanoelectronic devices.

The first principle study of magnetic, electronic, and optical properties of Co- and Mn-doped boron nitride nanosheets

In the present study, the magnetic, electronic, and optical properties of Co- and Mn-doped BN nanosheets [substituting one Mn(Co) atom on B (MnB or CoB), N (MnN or CoN), or two Mn(Co) atoms with B and its adjacent N atom (MnBN or CoBN) sites] for both perpendicular (E||c) and parallel (E||a) electromagnetic wave polarization have been investigated by the first principle calculations based on density functional theory. In this regard, optical parameters of Co/BN and Mn/BN including dielectric function, absorption, optical conductivity, extinction index, energy loss function, and reflectivity and refraction index are calculated. Magnetic investigations also show that compared to the pure BN sheet with 4.5 eV bandgap and zero magnetic moment, placing Co or Mn atom in the BN sheet decreases the bandgap and creates a net magnetic moment. Results inferred to the half-metallic behavior of MnB/BN and CoB/BN, and other doped structures become n-type semiconductor with a narrow bandgap. As can be seen, the optical and magnetic properties of Co- and Mn-doped BN monolayer improve their applications in the industry such as designing spintronic and optoelectronic devices.

Influence of external field direction on polarization rotation in antiferroelectric squaric acid H2C4O4

Using the previously developed model we explore the processes of polarization rotation in antiferroelectric crystals of squaric acid by the electric fields directed arbitrarily within the ac plane. Except for some particular directions of the field, the two-step polarization reorientation at low temperatures is predicted: first, to the noncollinear phase with perpendicular sublattice polarizations and then to the collinear ferroelectric phase. However, when the field is directed along the axis of spontaneous sublattice polarizations, the intermediate noncollinear phase is absent; when the field is at 45° to this axis, the field for transition to the ferroelectric phase tends to infinity. The ground state proton configurations and the directions of the sublattice polarization vectors are determined for all field orientations. The T-E phase diagrams are constructed for the fields directed along the diagonals of the ac plane and for the above discussed particular directions of the field.

Polarization Characteristics of the Near-Field Distribution of One-Dimensional Subwavelength Gratings

To improve the anti-laser damage performance of one-dimensional (1D) subwavelength gratings (SWGs), this paper proposes to reasonably reduce the peak electric field at the grating ridges to further reduce the laser damage caused by the electric field contribution. Based on Maxwell’s equations, the equations for solving the field intensity of the near-field distribution of the dielectric materials are derived. The numerical simulation theoretical model is described. A 1064 nm laser in the –y direction irradiates the geometric surfaces under two perpendicular polarization directions: perpendicular to the grating ridges (transverse magnetic wave (TM) or x-polarization) and parallel to the grating ridges (transverse electric wave (TE) or z-polarization). We discuss the effects of the profile shape, structural parameters and refractive index of the material on the near-field distribution at the 1D SWG ridges by using a finite element method (FEM). The near-field distribution is sensitive to the x- and z-polarization of incident light. The near-field distribution of the 1D SWGs for TM waves is modulated by the surface, whereas that for TE waves is similar to the distribution of the bare substrate. The results show that the near-field distribution of 1D SWGs greatly depends on the laser polarization direction.

Development of an optical pressure‐sensitive membrane based on plasmon resonance on a gold island film

AbstractIn this paper, an optical pressure‐sensitive membrane based on plasmon resonance absorption has been designed, fabricated, and demonstrated. The membrane utilizes plasmon resonance on a gold island film embedded in a polydimethylsiloxane (PDMS) layers, and the shift of the resonant wavelength was used as an indicator of pressure‐induced strain of the membrane. The membrane with total thickness of 100 µm was prepared with spin‐coating of PDMS and vacuum evaporation of gold island film with the nominal thickness of 10 nm. Pressure sensitivity of the fabricated membrane was demonstrated from the measurement of absorbance spectra and the maximum sensitivity of 0.35 nm/kPa was achieved by applying pressure up to 35 kPa. Plasmon resonance mode attributing to the pressure sensitivity has been analyzed through comparison between electromagnetic simulation and membrane stretching test. From the stretching test, red shifts of the resonant wavelength were obtained for both parallel and perpendicular polarizations to the tensile direction with the sensitivities of 0.372 and 0.134 nm/%, respectively. From the electromagnetic simulation, these red shifts can be attributed to both gap‐mode and deformation‐mode resonances of the gold island film.

Multiple scattering effects on intercept, size, polydispersity index, and intensity for parallel (VV) and perpendicular (VH) polarization detection in photon correlation spectroscopy

Dynamic light scattering (DLS) is well established for rapid size, polydispersity, and size distribution determination of colloidal samples. While there are limitations in size range, resolution, and concentration, the technique has found ubiquitous applications from molecules to particles. With the ease of use of today’s commercial DLS instrumentation comes an inherent danger of misinterpretation or misapplication at the borderlines of suitability. In this paper, we show how comparison of different polarization components can help ascertain the presence of unwanted multiple scattering, which can lead to false conclusions about a sample’s mean size and polydispersity. We find that the contribution of multiple scattering events effectively reduces both the measured scattering intensity and the apparent size from the autocorrelation function. The intercept of the correlation function may serve as an indicator of relative strength of single to multiple scattering. Furthermore, the abundance of single scattering events at measurement positions close to the cell wall results in an apparent increase in uniformity yielding a lower polydispersity index which is more representative of the physical system.

Resonant x-ray absorption of strong-field-ionized CF3Br

We report on an experimental and theoretical study of strong-field laser ionization of CF3Br followed by resonant x-ray absorption at the Br K-edge. Distinct 1s → 4p, 5p Rydberg transitions of Br q+ (q = 1–4) atomic ions are observed and identified with Hartree–Fock–Slater and relativistic configuration interaction calculations. Time-dependent density functional theory and ab initio molecular dynamics calculations were performed to simulate the dissociative ionization process and the molecular orbitals for the q = 1–4 charge states. Measurements were made with both parallel and perpendicular linear polarizations of the laser and x-rays, but dichroism was not observed, indicating negligible alignment by the laser ionization process. This result is explained by calculations on atomic Br and the molecular simulation.

Creation of tunable longitudinally polarized terahertz pulse carrying orbital angular momentum

There is a growing interest to the longitudinal electric field because of its applications in the particle acceleration, metallic particle trapping and optical data storage. When the longitudinal electric field is added by the vorticity at terahertz domain, this unique property can be have more potential for many applications. Here by applying two optical vortices through plasma, a scheme to produce the terahertz pulse carrying orbital angular momentum with the longitudinal polarized electric field is proposed. To excite the helicity of the terahertz pulse, the twisted input lasers are employed. Input pulses with the perpendicular polarization to the propagation path can generate a combined longitudinal and transversal polarized terahertz pulse. To separate the longitudinal polarized component of the radiated terahertz electric field, one can use the two orthogonal polarizers. Furthermore, the electric field components, radiation pattern and spectrum of emitted terahertz are analytically derived.

Generation of even and odd harmonics in the XUV region with controlling the relative delay and polarization of two-color fields

Abstract We report high harmonic generation in the extreme ultraviolet (XUV) region by using two-color laser fields at the wavelengths of 800 nm and 400 nm. With a Ti: sapphire femtosecond laser at a 10 Hz repetition rate efficient high harmonic generation was obtained in an argon gas medium with the IR field (ω) and its second harmonic (2ω) with parallel and perpendicular polarizations. The relative delay between the pulses is controlled via a Michelson interferometer arrangement. In addition to the odd high harmonic spectrum with frequencies (2n+1)ω, where n - integer number, also even spectral components 2nω are obtained, when the fields of the two colors are temporally overlapped and interact with the argon gas. Due to this overlap, the yield of odd harmonics can be increased as well. The calculations of electron trajectories within the semi-classical approach show differences in the action of the fields with parallel and perpendicular polarizations. For the former, there exist broad time intervals for returning electrons, and in the latter case there are only narrow intervals for possible solutions for each of the electron returns to the parent ion for a fixed phase difference between the ω and 2ω fields. By varying the relative delay between the two laser fields it is possible to spectrally enrich and enhance the produced XUV radiation or suppress it. The conclusions of the semi-classical approach were confirmed by calculations of the harmonic intensities within the strong field dipole approximation.

Antireflection Coating influences on the Quantum Efficiency and the Reflectivity of a GaAs / GaAS Solar Cell within the Visible Spectrum

A theoretical investigation of the change in reflectance of silicon carbide (SiC) as a function of the particle size was the main focus of the current research. In addition, a single layer of anti-reflection coating of a quarter the wavelength is designed and doped in gallium arsenide (GaAs/GaAs) solar cell. The efficiency of the cell is investigated in the range of (400-700 nm) using the Brus model and the theory of characteristic matrix in the case of vertical and 45° ray to the plane of the incidence. The max efficiency for the designed cell (Air/Nano SiC/(GaAs/GaAs) was (% 96.81) of the wavelength of 550 nm in the case of vertical incidence. While in the case of an incident ray of 45° to the plane of the incidence, the efficiency was (%92.99) for the perpendicular polarisation (S) and (%97.23) in the case of horizontal polarization (P). the thickness of the coating was (Ps=2.2 nm).