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Results for “Polarization state analyzer”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Ellipsometry

Ellipsometry is a technique often used to measure the thickness and properties of a thin film. This article covers the instrumental, theoretical, and practical aspects of this technique. Notably, different types of instruments including nulling ellipsometer, rotating compensator ellipsometer, and photoelastic modulator ellipsometer designs are presented. Elements of proper data analysis are also included, such as the use of an error-based figure of merit.

Complex reflection coefficients↗
DOE OSTI2024

Metasurface‐Based Mueller Matrix Microscope

In conventional optical microscopes, image contrast of objects mainly results from the differences in light intensity and/or color. Muller matrix optical microscopes (MMMs), on the other hand, can provide significantly enhanced image contrast and rich information about objects by analyzing their interactions with polarized light. However, state-of-the-art MMMs are fundamentally limited by bulky and slow polarization state generators and analyzers. Here, the study demonstrates a metasurface-based MMM, i.e., Meta-MMM, which is equipped with a chip-integrated, single-shot metasurface polarization state analyzer (Meta-PSA). The Meta-MMM is featured with high-speed measurement (≈2s per Muller matrix (MM) image), superior operation stability, dual-color operation, and high measurement accuracy (measurement error 1–2%) for MM imaging. The Meta-MMM is applied to nanostructure characterization, surface morphology analysis, and discovering birefringent structures in honeybee wings. As a result, the Meta-MMMs hold the promise to revolutionize various applications from biological imaging, medical diagnosis, and material characterization to industry inspection and space exploration.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Crystal orientation-dependent polarization state of high-order harmonics

We analyze the crystal orientation-dependent polarization state of extreme ultraviolet (XUV) high-order harmonics from bulk magnesium oxide crystals subjected to intense linearly polarized laser fields. We find that only along high-symmetry directions in crystals high-order harmonics follow the polarization direction of the laser field. In general, the polarization direction of high-order harmonics deviates from that of the laser field, and the deviation amplitude depends on the crystal orientation, harmonic order and the strength of the laser field. We use a real-space electron trajectory model to understand the crystal orientation-dependent polarization state of XUV harmonics. The polarization analysis allows us to track the motion of strong-field-driven electron in conduction bands in two dimensions. These results have implications in all-optical probing of atomic-scale structure in real-space, electronic band-structure in momentum space, and in the possibility of generating attosecond pulses with time-dependent polarization in a compact setup.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Observation of interface dependent spin polarized photocurrents in InAs/GaSb superlattice

In this letter, we investigated the spin polarized photocurrents excited by mid-infrared radiation and near-infrared radiation, respectively, in InAs/GaSb type II superlattices with different kinds of interfaces. By periodically varying the polarization state of the radiation, we analyzed Rashba-type and Dresselhaus-type spin polarized photocurrents, which present different features depending on the interface types and excitation conditions. Under mid-infrared excitation, the ratio of Rashba-type and Dresselhaus-type spin polarized photocurrents of the superlattice with InSb-like interface is obviously larger than that of the superlattice with GaAs-like interface, the ratio of the superlattice with alternate interface is in the middle. Whereas under near-infrared excitation, the ratios of the three superlattices are nearly the same. Further researches reveal the synactic effects of interface dependent strain and asymmetric interface potential on the spin splitting. Besides, the polarized Raman spectroscopies of these structures were also analyzed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Cold-air outbreaks in the continental US: Connections with stratospheric variations

Mid-latitude Northern Hemisphere extreme cold events continue to occur despite overall winter warming trends. These events have been linked to weakened stratospheric polar vortex (SPV) states. In this study, we analyze both the upper and lower polar stratosphere for links to extreme winter cold and snow in the continental US, finding two SPV variations of interest. The first features an upper-level vortex displaced toward western Canada and linked to northwestern US severe winter weather. The second features a weakened upper-level vortex displaced toward the North Atlantic and linked to central-eastern US severe winter weather. Both variations feature lower-level stretched vortices and stratospheric wave reflection. Since 2015, a northwestward shift in severe winter weather across the US is concurrent with an increase in the frequency of the westward-focused variation relative to the eastward-focused variation and a shift to more negative phases of the El Niño–Southern Oscillation.

Science & Technology - Other Topics↗
DOE OSTI2014

Magnetization stability analysis of the Stoner-Wohlfarth model under a spin-polarized current with a tilted polarization

The stationary-state solutions of magnetization dynamics under a spin-polarized current that was polarized in an arbitrary direction were investigated by solving the Landau-Lifshitz-Gilbert-Slonczewski equation for a single-domain magnet. Taking into consideration the uniaxial magnetic anisotropy, the equilibrium directions of the magnetization vectors were analytically obtained by solving an algebraic cubic equation. It was found that one to three pairs of magnetization equilibrium states existed, depending on the current intensity and the direction of the spin polarization. By numerically analyzing the stabilities of these equilibrium states, the threshold switching current for the reversing the magnetic vector was obtained under different current polarization configurations, which may be useful for use in future spintronics devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Edge states and phase diagram for graphene under polarized light

In this paper, we investigate the topological phase transitions in graphene under the modulation of circularly polarized light, by analyzing the changes of edge states and its topological structures. A full phase diagram, with several different topological phases, is presented in the parameter space spanned by the driving frequency and light strength. We find that the high-Chern number behavior is very common in the driven system. While the one-photon resonance can create the chiral edge states in the π-gap, the two-photon resonance will induce the counter-propagating edge modes in the zero-energy gap. When the driving light strength is strong, the number and even the chirality of the edge states may change in the π-gap. The robustness of the edge states to disorder potential is also examined. We close by discussing the feasibility of experimental proposals.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Floquet engineering of tilted and gapped Dirac bandstructure in 1T$$^\prime$$-MoS$$_2$$

Abstract We have developed a rigorous theoretical formalism for Floquet engineering, investigating, and subsequently tailoring most crucial electronic properties of 1T $$^\prime$$ ′ -MoS $$_2$$ 2 by applying an external high-frequency dressing field within the off-resonance regime. It was recently demonstrated that monolayer semiconducting 1T $$^\prime$$ ′ -MoS $$_2$$ 2 exhibits tunable and gapped spin- and valley-polarized tilted Dirac bands. The electron-photon dressed states depend strongly on the polarization of the applied irradiation and reflect a full complexity of the low-energy Hamiltonian for non-irradiated material. We have calculated and analyzed the properties of the electron dressed states corresponding to linear and circular polarization of a dressing field by focusing on their symmetry, anisotropy, tilting, direct and indirect band gaps. Circularly polarized dressing field is known for transition into a new electronic state with broken time-reversal symmetry and a non-zero Chern number, and therefore, the combination of these topologically non-trivial phases and transitions between them could reveal some truly unique and previously unknown phenomena and applications. We have also computed and discussed the density of states for various types of 1T $$^\prime$$ ′ -MoS $$_2$$ 2 materials and its modification in the presence of a dressing field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Strain effects on stability of topological ferroelectric polar configurations in (PbTiO3) n /(SrTiO3) n superlattices

The (PbTiO3)n/(SrTiO3)n (PTO/STO) superlattice system has been shown to exhibit interesting topological phases (e.g., vortices and skyrmions) in addition to normal ferroelectric domain states. Existing studies are mostly focused on the dependence of topological polar distributions and properties of PTO/STO superlattice on its periodicity. Here, we study the strain effect on the topological phase transitions and ferroelectric domain structures employing phase-field simulations. We summarized in an isotropic strain (in-plane misfit strain along the x direction is equal to that along the y direction) periodicity phase diagram displaying the stability regions of different polar topological states, including normal ferroelectric twins, vortices, skyrmions, and mixtures of vortices and twins. We also analyzed the polarization configurations under anisotropic in-plane strains (in-plane misfit strain along the x direction is not equal to that along the y direction) and demonstrated that the strain anisotropy can be used to tune the directions of vortex arrays along either the [100] pc or [010] pc directions or labyrinth vortex arrays. This work offers guidance to manipulating polar structures in the PTO/STO superlattices via strain engineering.

Physics↗
DOE OSTI2015

Electronic and optical properties of novel carbazole-based donor-acceptor compounds for applications in blue-emitting organic light-emitting diodes

We report that organic light-emitting diodes (OLEDs) have received a significant attention over the past decade due to their energy-saving potential. We have recently synthesized two novel carbazole-based donor-acceptor compounds and analyzed their optical properties to determine their suitability for use as blue emitters in OLEDs. These compounds show remarkable photo-stability and high quantum yields in the blue region of the spectrum. In addition, they have highly solvatochromic emission. In non-polar solvents, bright, blue-shifted (λmax ≈ 398 nm), and highly structured emission is seen. With increasing solvent dielectric constant, the emission becomes weaker, red-shifted (λmax ≈ 507 nm), and broad. We aim to determine the underlying cause of these changes. Electronic structure calculations indicate the presence of multiple excited states with comparable oscillator strength. These states are of interest because there are several with charge-transfer (CT) character, and others centered on the donor moiety. We theorize that CT states play a role in the observed changes in emission lineshape and may promote charge mobility for electrofluorescence in OLEDs. In the future, we plan to use Stark spectroscopy to analyze the polarity of excited states and transient absorption spectroscopy to observe the dynamics in the excited state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Effect of surface ionic screening on the polarization reversal scenario in ferroelectric thin films: Crossover from ferroionic to antiferroionic states

Nonlinear electrostatic interaction between the surface ions of electrochemical nature and ferroelectric dipoles gives rise to the coupled ferroionic states in nanoscale ferroelectrics. Here, we investigated the role of the surface ions formation energy value on the polarization states and polarization reversal mechanisms, domain structure and corresponding phase diagrams of ferroelectric thin films. Using 3D finite elements modeling we analyze the distribution and hysteresis loops of ferroelectric polarization and ionic charge, and dynamics of the domain states. These calculations performed over large parameter space delineate the regions of single- and poly- domain ferroelectric, ferroionic, antiferroionic and non-ferroelectric states as a function of surface ions formation energy, film thickness, applied voltage and temperature. We further map the analytical theory for 1D system onto effective Landau-Ginzburg free energy and establish the correspondence between the 3D numerical and 1D analytical results. In conclusion, this approach allows performing the overview of the ferroionic system phase diagrams and exploring the specifics of switching and domain evolution phenomena.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Z DECAYS TO TOP QUARKS

Z decays to top quark pairs—if kinematically possible—will provide an accurate measurement of the top quark mass in e + e - collisions. We study various distributions of leptons and jets in the final state for semileptonic quark decays. Fragmentation and polarization effects are analyzed. In addition to large longitudinal and transverse polarizations, a small normal t-quark polarization is built up by γ,Z interference and perturbative QCD corrections. We comment also briefly on polarization effects in the $t\bar{b}$ decays of W bosons that are hadronically produced.

Kuehn, J.↗
DOE OSTI2019

Coupled structural distortions, domains, and control of phase competition in polar SmBaMn 2 O 6

Materials with coupled or competing order parameters display highly tunable ground states, where subtle perturbations reveal distinct electronic and magnetic phases. These states generally are underpinned by complex crystal structures, but the role of structural complexity in these phases often is unclear. Here we use group-theoretic methods and first-principles calculations to analyze a set of coupled structural distortions that underlie the polar charge and orbitally ordered antiferromagnetic ground state of A -site ordered SmBaMn 2 O 6 . We show that these distortions play a key role in establishing the ground state and stabilizing a network of domain wall vortices. Furthermore, we show that the crystal structure provides a knob to control competing electronic and magnetic phases at structural domain walls and in epitaxially strained thin films. These results provide new understanding of the complex physics realized across multiple length scales in SmBaMn 2 O 6 and demonstrate a framework for systematic exploration of correlated and structurally complex materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Competition between Abelian and Zeeman magnetic field effects in a two dimensional ultracold gas of fermions

The ground state of ultracold fermions in the presence of effects of orbital and Zeeman magnetic fields is analyzed. Five different states are found: unpolarized superconducting state, partially and fully polarized normal states and phase separated regions, partially or fully polarized. The system, in the presence of orbital synthetic magnetic field effects, shows non-monotonous changes of the phase boundaries when electron concentration is varied. We observe not only reentrant phenomena, but also density dependent oscillations of different areas of the phase diagram. Moreover the chemical potential shows oscillatory behavior and discontinuities with respect to changes in the number of fermions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Disk-loss and disk-renewal phases in classical Be stars. II. Contrasting with stable and variable disks

Recent observational and theoretical studies of classical Be stars have established the utility of polarization color diagrams (PCDs) in helping to constrain the time-dependent mass decretion rates of these systems. We expand on our pilot observational study of this phenomenon, and report the detailed analysis of a long-term (1989-2004) spectropolarimetric survey of nine additional classical Be stars, including systems exhibiting evidence of partial disk-loss/disk-growth episodes as well as systems exhibiting long-term stable disks. After carefully characterizing and removing the interstellar polarization along the line of sight to each of these targets, we analyze their intrinsic polarization behavior. We find that many steady-state Be disks pause at the top of the PCD, as predicted by theory. We also observe sharp declines in the Balmer jump polarization for later spectral type, near edge-on steady-state disks, again as recently predicted by theory, likely caused when the base density of the disk is very high, and the outer region of the edge-on disk starts to self absorb a significant number of Balmer jump photons. The intrinsic V-band polarization and polarization position angle of γ Cas exhibits variations that seem to phase with the orbital period of a known one-armed density structure in this disk, similar to the theoretical predictions of Halonen and Jones. We also observe stochastic jumps in the intrinsic polarization across the Balmer jump of several known Be+sdO systems, and speculate that the thermal inflation of part of the outer region of these disks could be responsible for producing this observational phenomenon. Finally, we estimate the base densities of this sample of stars to be between ≈8 × 10{sup –11} and ≈4 × 10{sup –12} g cm{sup –3} during quasi steady state periods given there maximum observed polarization.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Tuning the polar states of ferroelectric films via surface charges and flexoelectricity

In this work, using the self-consistent Landau-Ginzburg-Devonshire approach we simulate and analyze the spontaneous formation of the domain structure in thin ferroelectric films covered with the surface screening charge represented by the Bardeen-type surface states. Hence we consider the competition between the screening and the domain formation as alternative ways to reduce the electrostatic energy and reveal unusual peculiarities of distributions of polarization, electric and elastic fields conditioned by the surface screening length and the flexocoupling strength. We have established that the critical thickness of the film and its transition temperature to a paraelectric phase strongly depend on the Bardeen screening length, while the flexocoupling affects the polarization rotation and closure domain structure. Furthermore the flexocoupling induces ribbon-like nano-scale domains in the film depth far from the top open surface, which might be related to the enigmatic polar nanoregions in relaxor ferroelectrics. Thus the joint action of the surface screening (originating from e.g. the adsorption of ambient ions or surface states) and flexocoupling may remarkably modify polar and electromechanical properties of thin ferroelectric films.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Polarization effects associated with thermal processing of HY-80 structural steel using high-power laser diode array

Localized heating of roughened steel surfaces using disperse laser light emitted from high power laser diode arrays was experimentally demonstrated and compared with theoretical predictions. The Fresnel equations were used to analyze the optical absorptivity in terms of the angle of incidence and polarization state to understand the laser-induced temperature rise of HY-80 steel plates under 383-612 W laser irradiation. Laser-induced, transient temperature distributions were directly measured using bulk thermocouple probes and thermal imaging. Finite element analysis yielded quantitative assessment of energy deposition and heat transport in HY-80 steel using absorptivity as a tuning parameter. The extracted absorptivity values ranged from 0.62 to 0.75 for S-polarized and 0.63 to 0.85 for P-polarized light, in agreement with partially oxidized iron surfaces. Microstructural analysis using electron backscatter diffraction revealed a heat affected zone for the highest temperature conditions (612 W, P-polarized) as evidence of rapid quenching and an austenite to martensite transformation. In conclusion, the efficient use of diode arrays for laser-assisted advanced manufacturing technologies such as hybrid friction stir welding is discussed.

36 MATERIALS SCIENCE↗