Perpendicular Polarization Research Articles

Divergence and efficiency optimization in polarization-controlled two-color high-harmonic generation

Improving the brightness of high-harmonic generation (HHG) sources is one of the major goals for next-generation ultrafast, imaging and metrology applications in the extreme-ultraviolet spectrum. Previous research efforts have demonstrated a plethora of techniques to increase the conversion efficiency of HHG. However, few studies so far have addressed how to simultaneously minimize the divergence and improve focusability, which all contribute to an increased brightness of the source. Here, we investigate how to improve both photon yield and divergence, which is directly linked to focusability, when adding the second harmonic to the fundamental driving field. We study the effects of the relative polarization in two-color HHG and compare the results to a one-color configuration. In a perpendicular two-color field, the relative phase between the two colors can be used to suppress or enhance recombination of either the long or the short trajectories. This allows to exert control over the divergence of the harmonics. In a parallel two-color field, the ionization rate is modified through the two-color phase, which selects trajectories during the ionization step. This enhances the total yield. We elaborate on the underlying mechanisms for parallel, perpendicular, and intermediate polarization angles, and confirm our experimental observations with simulations.

Mathematical Model of a Square Waveguide Polarizer with Diaphragms

The development of new mathematical model for guide polarization converter with diaphragms was carried out in the research by the method of wave matrices. In addition, numerical modeling of the performance of a polarizer with diaphragms is made by simulating the propagation of the fundamental modes with perpendicular linear polarizations. The wave matrix model was obtained by splitting the polarizer into separate structural elements. Each element was described by its own wave transmission matrices. As a result, a general wave scattering matrix was formed. Based on the elements this matrix the electromagnetic characteristics of the considered polarizer were obtained theoretically. In particular, complex reflection and transmission coefficients were calculated. Their modules and phases were analyzed in the frequency interval 10.7-12.8 GHz. To check the correctness of the obtained results an independent numerical simulation was carried out applying the finite element methodology in the frequency interval. The results of both approaches are in good agreement. The engineered converter of polarization with four diaphragms provides a reflection coefficient modulus of less than 0.14 and a transfer coefficient modulus of more than 0.99 for two orthogonal types of polarizations. As a result, a rigorous mathematical method was developed to analyze the elements of the scattering matrix of a waveguide polarizer with diaphragms. It can be used for the development of new broadband waveguide polarizers and waveguide filters based on diaphragm elements.

Polarized Raman spectroscopy of GaP nanowires under 5% elastic strain

Optical porperties of highly-strained gallium phosphide nanowires were investigated via polarized Raman spectroscopy. 5% elastic strain was created in individual nanowire lying on nickel substrate by the means of atomic force microscopy. Micro-Raman mapping along the nanowire cross section in parallel and perpendicular polarization was carried out. Strain-induced effects on transverse optical mode position and shape were analyzed. The pronounced splitting of the mode due to high level of strain was observed. It was found that in parallel polarization the mode shape is sensitive to the position of the pumping spot which can be attributed to enhanced light-nanowire coupling effects.

Re-investigation of the infrared spectrum of the NCN radical by laser magnetic resonance spectroscopy

The laser magnetic resonance (LMR) spectroscopic technique has been used to reinvestigate the mid-infrared spectrum of the NCN free radical in its Σg-3 ground electronic state. A liquid nitrogen-cooled carbon monoxide (CO) laser was used as a source of strong coherent radiation in the 1442–1484 cm−1 region of the infrared. Vibration-rotation transitions were brought into resonance with the laser frequency using magnetic flux densities up to 1.4 T. Spectra were recorded in both parallel (ΔMJ = 0) and perpendicular (ΔMJ = ±1) polarizations with ten CO laser lines. Over one hundred new absorption lines were observed in the LMR spectra and have been subsequently assigned to transitions in either the 301 fundamental band (near 1466.5 cm−1) or the 211301 hot band (near 1455.6 cm−1) of NCN in the Σg-3 ground state. An improved set of molecular parameters for NCN has been determined from a least-squares fit of all the available data on the infrared spectrum, provided by Fourier transform and LMR spectra. In the wake of an exhaustive analysis of the LMR spectra, several additional lines remain. Although chemical tests indicate these lines do not belong to NCN, it has not proved possible to identify their carrier(s).

Neural Network Topology-Based Terahertz Absorber Using Fractal Frequency Selective Surface

This work offers a new kind of polarization-insensitive, angular stable, tunable fractal frequency selective surface (FSS) based terahertz (THz) absorber. An equivalent circuit model (ECM) of the absorber is developed and impedance is obtained analytically. Further, an ECM-backed artificial neural network (ANN) approach is proposed and used to optimize the absorber to the desired frequency and bandwidth. The minimum mean square error between targeted and observed outputs is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.86\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> . The maximum absorption of 99% is achieved at a central frequency of 1.5 THz. The tunability is accomplished by varying the chemical potential ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{c}$ </tex-math></inline-formula> ) of the graphene layer introduced in the proposed absorbing structure. The resonance frequency shifts to 1.66 THz from 1.39 THz with a change in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{c}$ </tex-math></inline-formula> from 0.3eV to 0.6eV.The dual-band absorption peaks are noticed with fractal FSS based absorber within the operating frequency range of 0.1-4.0 THz. The maximum absorption of 0.99 and 0.98 at the resonant frequency of 1.0 THz and 3.1 THz with fractal FSS, respectively is achieved. Furthermore, the designed absorber works well for both perpendicular and parallel polarizations up to 60 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> angle of incidence. Moreover, the effect of structural parameters is also observed on the equivalent inductance and capacitance to understand the physics behind the structure. All the results obtained from ANN are verified with particle swarm optimization (PSO) and Whale optimization (WO) techniques. Good congruence among ANN, PSO, and WO results shows the effectiveness of the aforementioned technique. The possible applications of the proposed tunable absorber are THz imaging, sensing, detection, and stealth.

Thickness-dependent in-plane anisotropy of GaTe phonons

Gallium Telluride (GaTe), a layered material with monoclinic crystal structure, has recently attracted a lot of attention due to its unique physical properties and potential applications for angle-resolved photonics and electronics, where optical anisotropies are important. Despite a few reports on the in-plane anisotropies of GaTe, a comprehensive understanding of them remained unsatisfactory to date. In this work, we investigated thickness-dependent in-plane anisotropies of the 13 Raman-active modes and one Raman-inactive mode of GaTe by using angle-resolved polarized Raman spectroscopy, under both parallel and perpendicular polarization configurations in the spectral range from 20 to 300 cm−1. Raman modes of GaTe revealed distinctly different thickness-dependent anisotropies in parallel polarization configuration while nearly unchanged for the perpendicular configuration. Especially, three Ag modes at 40.2 ({text{A}}_{text{g}}^{1}), 152.5 ({text{A}}_{text{g}}^{7}), and 283.8 ({text{A}}_{text{g}}^{12}) cm−1 exhibited an evident variation in anisotropic behavior as decreasing thickness down to 9 nm. The observed anisotropies were thoroughly explained by adopting the calculated interference effect and the semiclassical complex Raman tensor analysis.

Electronic and optical properties of adsorbed of Zr-atom on vacancy-defective graphene: First principles calculations

The present work investigated the electronic and optical properties of adsorbed of Zr-atom on vacancy-defective graphene in the framework of density functional theory. For light polarization parallel and perpendicular, the dielectric function, absorption spectrum, reflectivity, refractive index, conductivity, and energy loss function of the systems have been calculated. Results indicate that the Zr adsorption system is a direct bandgap semiconductor. The adsorption system is transparent in the range of 7–9 eV under parallel polarization. In the visible range, the peaks of the absorption spectrum of the system are redshifted. Thus the Zr adsorption system has higher peak intensity in the Near-Infrared frequency. Under the perpendicular polarization, the reflectivity of the Zr adsorption system exhibits a reduced peak intensity and a new peak near 4 eV. We hope that our study would provide a constructive reference for applications of optoelectronic devices.

Polarization splitting with cubic crystals evaluated with synchrotron radiation.

X-ray polarization-splitting crystals separate incident x rays into two components with perpendicular polarization by Bragg reflections at 45° from paired sets of internal planes. Here, the polarization-splitting properties of a germanium crystal are verified using incompletely polarized synchrotron radiation. Cleaner data would have come from a beam with a higher degree of polarization, which is achievable with small changes in the experimental geometry.

Aggregation of Amphiphilic Carbocyanines: Fluorination Favors Cylindrical Micelles over Bilayered Tubes.

The synthesis of a new amphiphilic 5,5',6,6'-tetrachlorobenzimidacarbocyanine dye derivative with -(CH2)2-(CF2)5-CF3 chains attached to the nitrogen atoms in the 1,1'-position, CF8O3, is reported. Depending on the dye concentration and the addition of MeOH, CF8O3 forms J- and H-aggregates in aqueous solutions. The aggregation behavior was investigated using steady-state absorption, linear dichroism, and fluorescence spectroscopy, as well as by cryogenic transmission electron microscopy (cryo-TEM). The J-band of the MeOH-free solution is monomer-like, rather broad, and less red-shifted with respect to the monomer absorption, indicating weak excitonic coupling and disorder effects. Cryo-TEM reveals a diversity of supramolecular structures, wherein linear and branched cylindrical micelles dominate. It is concluded that the high stiffness of fluoroalkyl chains does not allow the chains to splay and completely fill up the hydrophobic gap between opposing chromophores. This destabilizes the bilayers and favors the micellar structure motifs instead. The aggregates appearing at 30% MeOH show a split absorption spectrum consisting of a broad blue-shifted H-band and an accompanying sharp red-shifted J-band with perpendicular polarizations. These HJ-type aggregates are also composed of micellar fibers, but these bundle into rope-like strands. For 10% MeOH, a narrow bilayered tube is the dominating morphology. The observed MeOH dependence of aggregation reveals a clear cosolvent effect.

A Scalable, Dual-Polarized Absorber Surface for Electromagnetic Energy Harvesting and Wireless Power Transfer

We present a dual-polarized electromagnetic (EM) energy-harvesting system that consists of a periodic absorber surface and a full-wave rectifier. The unit cell of the absorber is constructed using concentric bow-tie dipoles and channeling features that make it possible to efficiently combine and transfer the collected power from multiple unit cells. Simulation results are provided together with experimental verification demonstrating the strong absorption characteristics of the proposed energy harvesting surface. Overall radiation-to-DC conversion efficiency of the fabricated prototype was measured to be more than 60% under two perpendicular polarizations. The performance of the structure was further evaluated under various polarization angles and the results demonstrate that the proposed concept can be used to construct a scalable and polarization insensitive energy-harvesting system.

Optical Properties from a Single GaAs Quantum Dot Structure.

We observed exciton and biexciton states in a single GaAs quantum dot at 4 K using micro pho-toluminescence system and investigated power dependent photoluminescence measurements to identify both exciton and biexciton states. The biexciton and exciton states showed quadratic (a~2.2) and linear (a~0.95) increasing power factor, respectively. The large energy difference (~0.2 meV) from exciton states for the perpendicular polarization was observed.

Optical properties of silicene-dielectric interfaces from IR to far UV

Since the growth of single layer of Si has emerged, silicene became a potential candidate material to make up the disadvantage of graphene. In this paper, the complex surface conductivity is applied to characterize the properties of silicene and we investigate the optical characterization of silicene-dielectric interfaces from IR to far UV range. The silicene-Si and silicene-Ge interfaces along both parallel and perpendicular polarization directions of electromagnetic field with normal incidence are considered in this work. The optical properties of the silicene-dielectric systems proposed in this paper lay a foundation for the performance of complex silicene-based optoelectronic devices such as sensors, detectors, filters, UV absorbers and so on.

Thermoelectric and optical properties of 2D hexagonal Dirac material Be3X2 (X = C, Si, Ge, Sn): A density functional theory study

The thermoelectric and optical properties of the 2D hexagonal Dirac material Be3X2 (X=C, Si, Ge, Sn) have been investigated by the first-principles method. These structures have thermoelectric properties superior to graphene. The pristine Be3C2, Be3Si2, Be3Ge2 structures show an extraordinary large Seebeck coefficient, power factor, and ZT∼1 at a low temperature. The maximum thermoelectric efficiency is observed at T∼100–400 K and chemical potential in the range of −0.2 to 0.2 eV. The system performs better when they are n-doped. The optical properties indicate a contribution from both interband and intraband transitions. At a low frequency, the system shows optically metallic and semiconducting characteristics for parallel and perpendicular polarization of incident light, respectively. The materials behave as optically transparent for visible light. A σ–σ∗ interband transition is observed in the UV region of the electromagnetic spectrum. Both π and π+σ plasmon peaks are identified in the infrared and UV regions, respectively. All these intriguing properties of the Be3X2 monolayer may motivate fabricating this material and its application in smart thermoelectric and opto-electronic devices.

Linear optical properties of a linear chain of interacting gold nanoparticles

In a Drude-like model for the conduction electrons of metal nanoparticles (MNPs) in a periodic linear chain, considering dipole-dipole interactions of adjacent particles, an analytical expression is derived for each particle permittivity for two different polarizations of incident light: parallel with and perpendicular to the chain line. A numerical analysis is carried out for a chain including 10 identical gold nanoparticles (NPs) for two different sizes of NPs and two different host media: air and glass. It is shown that in the parallel case of polarization, interaction of NPs leads to a substantial increase in the extinction cross section and the redshift of the surface plasmon resonance (SPR) wavelength. In comparison with the linear properties of a single NP, the second and penultimate particles have the most increase in the extinction cross section and SPR wavelength displacement while the first and last particles experience the least variations due to the mutual interactions. For the perpendicular polarization, inversely, the dipolar coupling causes a decrease in extinction cross section of all particles and the blue-shift of SPR wavelength. For the parallel polarization, the absolute values of the real and imaginary parts of complex permittivity of each MNP decrease in comparison with the single particle case while they increase for the perpendicular state of polarization.

‘Effect of yarn composition and fabric weave design on microwave and EMI shielding properties of hybrid woven fabrics’

Ring spun composite yarn (RCY; 755 denier) with linear resistance of 172 Ω/m is prepared with stainless steel (SS) fibre and polyester fibre in ratio of 80%: 20% (w/w). Sheath core yarn system, core being ring spun yarn and PET fibre as sheath material is prepared in various fibre compositions adopting friction spinning technique. For microwave interaction and EMI shielding, hybrid woven fabrics are prepared using sheath-core yarn in weft and SS/PET blended yarn (20% SS/80% PET) in warp in cell structured and rib structured weave design. Samples of woven fabric were evaluated for microwave and EMI shielding properties in frequency range of 8.2–18.0 GHz in parallel and perpendicular polarisation of electromagnetic wave (em wave). Samples having conducting yarn in warp and weft both have shown high reflection in both polarisation of em wave. Sample containing metal fibre content of 32.58% (w/w) prepared in cell-structured weave design containing 1330 and 2017 denier sheath-core yarn in weft and 165 denier (20% SS/80% PET) blended yarn in warp offered reflection of 89.4922–59.9864% in parallel mode and 92.8135–80.0789% in perpendicular mode. This offered EMI shielding of −30.9601 to −35.4659 dB in perpendicular and −17.0209 to −11.2131 dB in parallel mode in 8.2 − 18.0 GHz. Woven fabrics are highly breathable, its air permeability lies in the range of 22.5–26.2 ft3/ft2/s. It inherits high aesthetic values. This hybrid woven fabric finds potential applications in radar camouflage, protection of human being from hazardous effect of microwaves, EMI shielding and electrostatic discharging cover materials, etc.

Tunable band gap energy of single-walled zigzag ZnO nanotubes as a potential application in photodetection

ZnO nanotubes play a substantial role in various optoelectronic applications such as light-emitting diodes, solar cells and photodetectors. In this study, the structural, electronic, and optical effects of (n,0) single-walled ZnO nanotubes with different radius are discussed. An ab-initio approach of density functional theory with the generalized gradient approximation has been done by Quantum ESPRESSO software on nanotubes with n = 3 to 6. All simulated ZnO nanotubes illustrate semiconducting behavior, which due to the quantum confinement effect, the band gap value decreases by the increase in diameter. Moreover, optical characteristics including dielectric function ε(ω), refractive index n(ω), optical absorption coefficient α(ω), conductivity σ(ω), energy loss spectrum L(ω) and reflectivity R(ω) have been analyzed and compared. The predicted optical features show that the mentioned nanotubes transmit light in perpendicular polarization better than parallel one and present superior reflect characters. Additionally, ZnO NTs act as a good absorbent in the visible wavelength which they can absorb various colors of the visible spectrum or even UV emission by altering the number of n. This ability turns ZnO NTs into remarkable photodetectors. Furthermore, according to optical characteristics like energy loss spectrum and dielectric function, it is obvious that results are approximately similar for different nanotubes and despite the miner red-shift of the position of the main peak, their appearance is close to each other. Therefore, ZnO NTs can be utilized in various applications such as optical filters, polarizers, and UV shields.

Stochastic electron motion in colliding plane waves.

The stochastic dynamics of an electron in counterpropagating linearly polarized laser beams is analyzed using a recently developed 3/2-dimensional Hamiltonian approach. It is shown that perpendicular canonical momenta suppress stochasticity, helping to explain the results from recently reported numerical studies of stochastic dynamics in a similar setting. The stochasticity in a perpendicular polarization setup is demonstrated. Lastly, the impact of radiation friction effects is considered, and shown to be negligible in the classical radiation reaction limit.

Polarization of hard X-ray dielectronic satellite lines from Na-like W ions

One of the important signatures of non-thermal high-atomic-number multiply ionized plasmas is polarization of hard x-ray line emission. Atomic processes in laboratory and astrophysical plasmas with anisotropic electron distribution that can lead to such polarization include dielectronic recombination. All previous research on x-ray line polarization of dielectronic satellite lines was mostly focused on K-shell radiation. Here we present one of the first studies of polarization of L-shell dielectronic satellite lines using the hard x-ray spectra of Na-like W produced by dielectronic recombination. Polarization of dielectronic satellites is calculated using two approaches: density matrix formalism and the FAC code. The most intense dielectronic satellite lines of Na-like W appeared to be positively polarized with the maximum degree of polarization between 0.4545 and 0.6. Polarization-dependent dielectronic satellite spectra of Na-like W are calculated with a gaussian electron distribution function centered at the beam energies from 2400 eV to 4100 eV. Such spectra cover the spectral range from 1.19 Å to 1.38 Å with each spectrum including two traces of line intensities associated with the parallel polarization and perpendicular polarization state. The polarization-dependent spectra were found to be strongly dependent on the energy of the electron beam which can be used for the development of x-ray plasma polarization spectroscopy to study non-thermal multiply ionized W plasmas. Radiative and polarization properties of W radiation studied in this paper are important for fusion research.

Polarization rotation by external electric field in the two-dimensional antiferroelectric squaric acid H2C4O4

A pseudospin model for description of the influence of the electric field, confined to the plane of sublattice polarization, on the two-dimensional squaric acid antiferroelectrics is developed. The system behavior is analyzed in terms of the parameters of ferroelectric and antiferroelectric ordering, as well as the non-collinearity angle $\theta$, which is the angle between sublattice polarizations. The temperature-electric field $T-E_1$ phase diagram is constructed. Most of the field-induced transitions are found to be associated with polarization rotation. The observed phases include the collinear ferroelectric and non-collinear ferrielectric with almost antiparallel and perpendicular polarizations of the sublattices, respectively. The diagram also contains two regions, where the non-collinearity angle varies continuously between, nominally, 0 and 90$^\circ$ and between 90$^\circ$ and 180$^\circ$. The first and second order transition lines, supercritical lines, critical end points, and critical points on the $T-E_1$ phase diagram are detected.

Phase-difference imaging based on FINCH

The diffraction theory was used to calculate the point spread function (PSF) of a typical Fresnel incoherent correlation holography (FINCH) system. It was found that the phase of the reconstructed image corresponds to the phase difference between the original points in two mutually perpendicular polarization directions. The experimental results show that the FINCH system with reasonable parameters can realize the phase-difference imaging of objects and measure the phase difference of cross-polarization directions in birefringent materials.