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Articles 1 - 30 of 59
Full-Text Articles in Physics
Light Induced Structures In Liquid Crystalline Side-Chain Polymers With Azobenzene Functional Groups, O. Yaroschuk, Tatiana Sergan, J. Lindau, S. Lee, J. Kelly, Liang-Chy Chien
Light Induced Structures In Liquid Crystalline Side-Chain Polymers With Azobenzene Functional Groups, O. Yaroschuk, Tatiana Sergan, J. Lindau, S. Lee, J. Kelly, Liang-Chy Chien
Liang-Chy Chien
We applied ellipsometry to study the distribution of azobenzene fragments in the films of two types of comblike polymers with azobenzene moieties in the side chains before and after ultraviolet ~UV! light irradiation. The polymer with an alkyl chain at the end of the azobenzene fragment forms structures with preferred homeotropic alignment of the fragments. Irradiation of this polymer with nonpolarized UV light at normal incidence induces a homeotropic alignment of azobenzene fragments. Oblique irradiation induces tilted structures. Polarized UV light irradiation at normal beam incidence induces biaxial structures with a fanlike distribution of azobenzene fragments and preferably out-of-plane alignment. …
Short Pitch Cholesteric Electro-Optical Device Stabilized By Nonuniform Polymer Network, Sang Kim, Liang-Chy Chien
Short Pitch Cholesteric Electro-Optical Device Stabilized By Nonuniform Polymer Network, Sang Kim, Liang-Chy Chien
Liang-Chy Chien
We have developed a method for stabilization of the uniform lying helix (ULH) texture of short pitch cholesterics in an electro-optical device, based on the flexoelectro-optic effect in such a texture. By using a small concentration of photoreactive liquid crystal monomer (less than 5 wt. %) and selecting the illumination conditions, we were able to create a nonuniform polymeric network in the liquid crystal bulk (localized essentially at both substrate surfaces) which stabilized efficiently the amplitude and the phase modulation modes of the device. Most importantly, the effect of the residual birefringence of the polymeric network in the field-unwound state …
Structure And Morphology Of Polymer-Stabilized Cholesteric Diffraction Gratings, Shin-Woong Kang, Samuel Sprunt, Liang-Chy Chien
Structure And Morphology Of Polymer-Stabilized Cholesteric Diffraction Gratings, Shin-Woong Kang, Samuel Sprunt, Liang-Chy Chien
Liang-Chy Chien
We report a study of polymer network morphology in planar diffraction gratings formed from polymer-stabilized cholesteric liquid crystals. Photopolymerizing a mesogenic monomer yields a regular sawtooth morphology, composed of polymer sheets running at an acute angle between thick, uniformly aligned bundles which reside on the opposing substrates. To explain this morphology and evidence of two grating vectors in the diffraction pattern, we propose a model for the liquid-crystal director where out-of-phase twists at the surfaces gear into an interior twist, which has half the period of the surface twist, via splay distortions running between the substrates. The morphology also changes …
Control Of Reflectivity And Bistability In Displays Using Cholesteric Liquid-Crystals, Deng-Ke Yang, John West, Liang-Chy Chien, J. Doane
Control Of Reflectivity And Bistability In Displays Using Cholesteric Liquid-Crystals, Deng-Ke Yang, John West, Liang-Chy Chien, J. Doane
Liang-Chy Chien
It is demonstrated that the reflective properties and bistability of cholesteric liquid crystals can be controlled by proper surface treatment and dispersed polymers. Dispersing a polymer in the liquid crystal or using a cell with an inhomogeneous surface anchoring creates permanent defects which result in long-term bistability, high contrast at large viewing angles, and gray scale. The wide-angle, reflective feature makes cholesteric materials suitable for displays without backlights and bistability provides flicker-free operation.
Field-Induced And Polymer-Stabilized Two-Dimensional Cholesteric Liquid Crystal Gratings, Shin-Woong Kang, Liang-Chy Chien
Field-Induced And Polymer-Stabilized Two-Dimensional Cholesteric Liquid Crystal Gratings, Shin-Woong Kang, Liang-Chy Chien
Liang-Chy Chien
The authors experimentally demonstrate an electrically switchable gratings based on polymer-stabilized, field-induced two-dimensional square-lattice pattern of a cholesteric liquid crystal. A dependence of the two-dimensional diffraction patterns with the magnitude of applied voltage is observed for before and after the polymer stabilization. The diffraction efficiency reaches 84% calculated for the zero order light intensity at the applied voltage of 0.23 V/mu m for a 10 mu m thick sample.
Dynamical Studies Of Gratings Formed In Polymer-Dispersed Liquid Crystal Films, Andy Fuh, T. Ko, M. Tsai, C. Huang, Liang-Chy Chien
Dynamical Studies Of Gratings Formed In Polymer-Dispersed Liquid Crystal Films, Andy Fuh, T. Ko, M. Tsai, C. Huang, Liang-Chy Chien
Liang-Chy Chien
The use of polymer-dispersed liquid crystal films to fabricate gratings was demonstrated. The written gratings are permanent, but are electrically switchable. In this article, we report the results obtained from the dynamical studies of gratings formed in polymer-dispersed liquid crystal films having various liquid crystal-polymer mixing ratios. The results showed that during the initial phases of formation, a thermal grating effect dominated. Later, it was offset or quenched by the photopolymerization effect which eventually dominated and determined the characteristics of the final grating.
Photoinduced Three-Dimensional Orientational Order In Side Chain Liquid Crystalline Azopolymers, O. Yaroshchuk, K. Kiselev, Yu. Zakrevskyy, T. Bidna, J. Kelly, Liang-Chy Chien, J. Lindau
Photoinduced Three-Dimensional Orientational Order In Side Chain Liquid Crystalline Azopolymers, O. Yaroshchuk, K. Kiselev, Yu. Zakrevskyy, T. Bidna, J. Kelly, Liang-Chy Chien, J. Lindau
Liang-Chy Chien
We apply experimental technique based on the combination of methods dealing with principal refractive indices and absorption coefficients to study the photoinduced three-dimensional (3D) orientational order in the films of liquid crystalline (LC) azopolymers. The technique is used to identify 3D orientational configurations of trans azobenzene chromophores and to characterize the degree of ordering in terms of order parameters. We study two types of LC azopolymers which form structures with preferred in-plane and out-of-plane alignment of azochromophores, respectively. Using irradiation with the polarized light of two different wavelengths, we find that the kinetics of photoinduced anisotropy can be dominated by …
Nematic Director Orientation In A Liquid-Crystal-Dispersed Polymer - A Deuterium Nmr Approach, Ralf Stannarius, G. Crawford, Liang-Chy Chien, J. Doane
Nematic Director Orientation In A Liquid-Crystal-Dispersed Polymer - A Deuterium Nmr Approach, Ralf Stannarius, G. Crawford, Liang-Chy Chien, J. Doane
Liang-Chy Chien
The nuclear-magnetic-resonance (NMR) technique is employed to liquid-crystal-dispersed-polymer (LCDP) systems. Deuterium NMR is used to determine director distributions in LCDP cells in the presence of a magnetic field. The samples consist of a nematic liquid crystal mixed with small percentages of a monomer that is polymerized under different conditions after dissolving it in the liquid crystal. NMR spectra of the deuterated liquid-crystal molecules give information on orientation and order in such systems. The orientation of the polymer skeleton formed during the polymerization is found to be stable. It determines the orientation of the nematic director even in the presence of …
Piezoelectric Effects In Cholesteric Elastomer Gels, C. C. Chang, Liang-Chy Chien, R. Meyer
Piezoelectric Effects In Cholesteric Elastomer Gels, C. C. Chang, Liang-Chy Chien, R. Meyer
Liang-Chy Chien
We report a piezolectric effect in cholesteric liquid crystalline elastomer gels. When we apply a shear stress to a cholesteric elastomer gel in the direction perpendicular to its helical axis, a polarization can be induced in the direction perpendicular to both the stress and the helix. This experimental observation agrees with the theory proposed by Pelcovits and Meyer [J. Phys. II France 5, 877 (1995)].
Formation And Localization Of Internal Polymer Columnar Structures In Liquid Crystal Cells, Qingbing Wang, Liang-Chy Chien, Satyendra Kumar
Formation And Localization Of Internal Polymer Columnar Structures In Liquid Crystal Cells, Qingbing Wang, Liang-Chy Chien, Satyendra Kumar
Liang-Chy Chien
Internal polymer columnar structures in liquid crystal (LC) cells have been produced using the method of thermally-induced phase separation of LC/prepolymer solution and solidified by photopolymerization. These polymer columns adhere to both substrates and enhance control of the LC cell spacing and mechanical stability. The existence and profile of the polymer columns were investigated by optical and scanning electron microscopy techniques. Supertwisted nematic LC cells with polymer columnar structures have been constructed using this method and their electro-optical characteristics measured.
Double Twist In Helical Polymer "Soft" Crystals, Christopher Li, Stephen Cheng, Jason Ge, Feng Bai, John Zhang, Ian Mann, Frank Harris, Liang-Chy Chien, Donghang Yan, Tianbai He, Bernard Lotz
Double Twist In Helical Polymer "Soft" Crystals, Christopher Li, Stephen Cheng, Jason Ge, Feng Bai, John Zhang, Ian Mann, Frank Harris, Liang-Chy Chien, Donghang Yan, Tianbai He, Bernard Lotz
Liang-Chy Chien
In natural and synthetic materials having non-racemic chiral centers, chirality and structural ordering each play a distinct role in the formation of ordered states. Configurational chirality can be extended to morphological chirality when the phase, structures possess low liquid crystalline order. In the crystalline states the crystallization process suppresses the chiral helical morphology due to strong ordering interactions, In this Letter, we report the first observation of helical single lamellar crystals of synthetic non-racemic chiral polymers. Experimental evidence shows that the molecular chains twist along both the long and short axes of the helical lamellar crystals, which is the first …
Liquid-Crystal Photoalignment Using Low-Molecular-Weight Photo-Cross-Linkable Composites, O. Yaroshchuk, L Cada, M. Sonpatki, Liang-Chy Chien
Liquid-Crystal Photoalignment Using Low-Molecular-Weight Photo-Cross-Linkable Composites, O. Yaroshchuk, L Cada, M. Sonpatki, Liang-Chy Chien
Liang-Chy Chien
A liquid-crystal (LC) photoalignment method, based on the use of low-molecular-weight photo-cross-linkable (LMWPC) composites is proposed. The basic idea of this method is that cross linking or both cross linking and polymerization of LMWPC composites are realized immediately on the substrate simultaneously with the photoalignment or as a stage of the backing process. Providing the advantages of a conventional photoalignment method, the use of LMWPC composites simplifies the synthesis and alignment procedure, makes possible wide range control of pretilt angles, and enhances the thermal stability of the LC alignment. The abilities of this method are demonstrated using a series of …
Cholesteric Liquid-Crystal Polymer Dispersion For Haze-Free Light Shutters, Deng-Ke Yang, Liang-Chy Chien, J. Donae
Cholesteric Liquid-Crystal Polymer Dispersion For Haze-Free Light Shutters, Deng-Ke Yang, Liang-Chy Chien, J. Donae
Liang-Chy Chien
A new dispersion involving a polymer in low concentration with a cholesteric liquid crystal is reported. Two types of light modulators from these materials are described as a normal mode shutter which is opaque (light scattering) in the field-OFF state and transparent in the field-ON state and a reverse-mode shutter with the opposite field conditions. The transparent state of both cells is haze-free for all viewing angles making the material attractive for window applications and direct view displays.
Effect Of A Polymer Network On The Alignment And The Rotational Viscosity Of A Nematic Liquid-Crystal, Antal Jákli, D. Kim, Liang-Chy Chien, A. Saupe
Effect Of A Polymer Network On The Alignment And The Rotational Viscosity Of A Nematic Liquid-Crystal, Antal Jákli, D. Kim, Liang-Chy Chien, A. Saupe
Liang-Chy Chien
Polymer dispersions were made by photoinduced polymerization of 4,4'-bisacryloyl-biphenyl in liquid crystal 4-4'-cyano pentyl biphenyl as nematic solvent. Samples were prepared with 0.5, 1, and 1.5 wt % monomer. The polymerization was done in the isotropic phase. The rotational viscosities of the two lower concentration samples increased only moderately after UV curing (3 mW/cm2, 25 min). The 1.5 wt % sample gave under the same condition a nematic with a fairly rigid anisotropic network that did not realign in magnetic field up to 20 kG. We estimate that the mesh size of the network was in the order of 1 …
Steady-State Aerosol Distributions In The Extra-Tropical, Lower Stratosphere And The Processes That Maintain Them, J. Wilson, Shan-Hu Lee, J. Reeves, C. Brock, H. Jonsson, B. Lafleur, M. Loewenstein, J. Podolske, E. Atlas, K. Boering, G. Toon, D. Fahey, T. Bui, G. Diskin, F. Moore
Steady-State Aerosol Distributions In The Extra-Tropical, Lower Stratosphere And The Processes That Maintain Them, J. Wilson, Shan-Hu Lee, J. Reeves, C. Brock, H. Jonsson, B. Lafleur, M. Loewenstein, J. Podolske, E. Atlas, K. Boering, G. Toon, D. Fahey, T. Bui, G. Diskin, F. Moore
Shan-Hu Lee
Measurements of aerosol, N2O and OCS made in the Northern Hemisphere below 21 km altitude following the eruption of Pinatubo are presented and analyzed. After September 1999, the oxidation of OCS and sedimentation of particles in the extra-tropical overworld north of 45 N are found to maintain the aerosol in a steady state. This analysis empirically links precursor gas to aerosol abundance throughout this region. These processes are tracked with age-of-air which offers advantages over tracking as a function of latitude and altitude. In the extra-tropical, lowermost stratosphere, normalized volume distributions appear constant in time after the fall of 1999. …
Laboratory Studies Of H2so4/H2o Binary Homogeneous Nucleation From The So2+Oh Reaction: Evaluation Of The Experimental Setup And Preliminary Results, L. Young, D. Benson, F. Kameel, J. Pierce, H. Junninen, M. Kulmala, Shan-Hu Lee
Laboratory Studies Of H2so4/H2o Binary Homogeneous Nucleation From The So2+Oh Reaction: Evaluation Of The Experimental Setup And Preliminary Results, L. Young, D. Benson, F. Kameel, J. Pierce, H. Junninen, M. Kulmala, Shan-Hu Lee
Shan-Hu Lee
Binary homogeneous nucleation (BHN) of sulphuric acid and water (H2SO4/H2O) is one of the most important atmospheric nucleation processes, but laboratory observations of this nucleation process are very limited and there are also large discrepancies between different laboratory studies. The difficulties associated with these experiments include wall loss of H2SO4 and uncertainties in estimation of H2SO4 concentration ([H2SO4]) involved in nucleation. We have developed a new laboratory nucleation setup to study H2SO4/H2O BHN kinetics and provide relatively constrained [H2SO4] needed for nucleation. H2SO4 is produced from the SO2+OH→HSO3 reaction and OH radicals are produced from water vapor UV absorption. The …
Ternary Homogeneous Nucleation Of H2so4, Nh3, And H2o Under Conditions Relevant To The Lower Troposphere, D. Benson, J. Yu, A. Markovich, Shan-Hu Lee
Ternary Homogeneous Nucleation Of H2so4, Nh3, And H2o Under Conditions Relevant To The Lower Troposphere, D. Benson, J. Yu, A. Markovich, Shan-Hu Lee
Shan-Hu Lee
Ternary homogeneous nucleation (THN) of H2SO4, NH3 and H2O has been used to explain new particle formation in various atmospheric regions, yet laboratory measurements of THN have failed to reproduce atmospheric observations. Here, we report first laboratory observations of THN made under conditions relevant to the lower troposphere ([H2SO4] of 106–107 cm−3, [NH3] of 0.08–20 ppbv, and a temperature of 288 K). Our observations show that NH3 can enhance atmospheric H2SO4aerosol nucleation and the enhancement factor (EF) in nucleation rate (J) due to NH3 (the ratio of Jmeasured with vs. without NH3) increases linearly with increasing [NH3] and increases with …
The Effects Of Airmass History On New Particle Formation In The Free Troposphere: Case Studies, D. Benson, Li-Hao Young, Shan-Hu Lee, T. Campos, D. Rogers, J. Jensen
The Effects Of Airmass History On New Particle Formation In The Free Troposphere: Case Studies, D. Benson, Li-Hao Young, Shan-Hu Lee, T. Campos, D. Rogers, J. Jensen
Shan-Hu Lee
Recent aircraft studies showed that new particle formation (NPF) is very active in the free troposphere. And, these observations lead to a new question: when does NPF not occur? Here, we provide case studies to show how different meteorological parameters affect NPF in the upper troposphere, using the aerosol size distributions measured at latitudes from 18° N–52° N and altitudes up to 14 km during the NSF/NCAR GV Progressive Science Missions. About 95% of the total samples showed the NPF feature with median number concentrations of particles with diameters from 4 to 9 nm (N4–9), 288±199 cm−3, and the total …
Uncertainty Associated With Modeling The Global Ionosphere, Janelle Jenniges, Ariel Acebal, Larry Gardner, Robert Schunk, Lie Zhu
Uncertainty Associated With Modeling The Global Ionosphere, Janelle Jenniges, Ariel Acebal, Larry Gardner, Robert Schunk, Lie Zhu
Janelle V Jenniges
A study has been conducted of the effect that different physical assumptions have on global models of the electron density distribution. The study was conducted with the Ionosphere Forecast Model (IFM) and the Ionosphere Plasmasphere Model (IPM) developed by Utah State University. Both physics-based, time-dependent, global models use the same empirical models for the neutral atmosphere (MSIS) and neutral wind (Horizontal Wind Model, HWM), but the altitude range, thermal structure, number of ion species, and magnetic 2ield are different. The IFM covers the altitude range from 90-1400 km, calculates the densities for four ions (NO+, O2+, N2+, O+), has a …
Electron Energy Dependent Charging Effects Of Multilayered Dielectric Materials, Gregory Wilson, Jr Dennison, Amberly Evans, Justin Dekany
Electron Energy Dependent Charging Effects Of Multilayered Dielectric Materials, Gregory Wilson, Jr Dennison, Amberly Evans, Justin Dekany
Gregory Wilson
Measurements of the charge distribution in electron-bombarded, thin-film, multilayer dielectric samples showed that charging of multilayered materials evolves with time and is highly dependent on incident energy; this is driven by electron penetration depth, electron emission and material conductivity. Based on the net surface potential’s dependence on beam current, electron range, electron emission and conductivity, measurements of the surface potential, displacement current and beam energy allow the charge distribution to be inferred. To take these measurements, a thin-film disordered SiO2 structure with a conductive middle layer was charged using 200 eV and 5 keV electron beams with regular 15 s …
Electron Induced Charging And Arcing Of Multilayered Dielectric Materials, Jr Dennison, Gregory Wilson, Amberly Evans, Justin Dekany
Electron Induced Charging And Arcing Of Multilayered Dielectric Materials, Jr Dennison, Gregory Wilson, Amberly Evans, Justin Dekany
Gregory Wilson
Measurements of the charge distribution in electron-bombarded, thin-film, multilayered dielectric samples showed that charging of multilayered materials evolves with time and is highly dependent on incident energy; this is driven by electron penetration depth, electron emission and material conductivity. Based on the net surface potential’s dependence on beam current, electron range, electron emission and conductivity, measurements of the surface potential, displacement current and beam energy allow the charge distribution to be inferred. To take these measurements, a thin-film disordered SiO2 structure with a conductive middle layer was charged using 200 eV and 5 keV electron beams with regular 15 s …
Approximation Of Range In Materials As A Function Of Incident Electron Energy, Gregory Wilson, Jr Dennison
Approximation Of Range In Materials As A Function Of Incident Electron Energy, Gregory Wilson, Jr Dennison
Gregory Wilson
A simple composite analytic expression has been developed to approximate the electron range in materials. The expression is applicable over more than six orders of magnitude in energy (<10 eV to >10 MeV) and range (10-9 m to 10-2 m), with uncertainty of ≤20% for most conducting, semiconducting and insulating materials. This is accomplished by fitting data from two standard NIST databases [ESTAR for the higher energy range and the electron IMFP (inelastic mean free path) for the lower energies]. In turn, these data have been fit with well-established semi-empirical models for range and IMFP that are related to standard materials properties …
Power And Charge Deposition In Multilayer Dielectrics From Monoenergetic Electron Bombardment, Gregory Wilson, Amberly Evans, Justin Dekany, Jr Dennison
Power And Charge Deposition In Multilayer Dielectrics From Monoenergetic Electron Bombardment, Gregory Wilson, Amberly Evans, Justin Dekany, Jr Dennison
Gregory Wilson
Power and charge deposition in multilayer dielectrics from electron bombardment is dependent upon the flux and electron range of the electron beam, where the range,--a lso known as the penetration depth—is dependent upon the incident beam energy. Using the Continuous Slow Down Approximation (CSDA), a composite analytical formula has been developed to relate the electron range to the dose rate and subsequently to the deposited power in each subsequent layer. Based on the constituent layer geometry and material , the deposited charge can also be inferred. To validate these models two separate experiments were conducted, one based on the net …
Temperature Dependence Of Sio2 Electron-Induced Cathodoluminescence, Amberly Evans, Gregory Wilson, Jr Dennison
Temperature Dependence Of Sio2 Electron-Induced Cathodoluminescence, Amberly Evans, Gregory Wilson, Jr Dennison
Gregory Wilson
No abstract provided.
Low Temperature Cathodoluminescence Of Space Observatory Materials, Amberly Evans, Gregory Wilson, Justin Dekany, Alec Sim, Jr Dennison
Low Temperature Cathodoluminescence Of Space Observatory Materials, Amberly Evans, Gregory Wilson, Justin Dekany, Alec Sim, Jr Dennison
Gregory Wilson
In recent charging studies, a discernable glow was detected emanating from sample surfaces undergoing electron beam bombardment that resulted from a luminescent effect termed cathodoluminescence. This suggests that some of the materials used as optical elements, structural components, and thermal control surfaces in the construction of space-based observatories might luminesce when exposed to sufficiently energetic charged particle fluxes from the space plasma environment. If these visible, infrared and ultraviolet emissions are intense enough, they can potentially produce optical contamination detrimental to the performance of the observatory optical elements and sensors, and act to limit their sensitivity and performance windows. As …
Extending The Band Model Of Disordered Sio2 Through Cathodoluminescence Studies, Amberly Evans, Gregory Wilson, Jr Dennison, Justin Dekany
Extending The Band Model Of Disordered Sio2 Through Cathodoluminescence Studies, Amberly Evans, Gregory Wilson, Jr Dennison, Justin Dekany
Gregory Wilson
Optical coatings of disordered thin film SiO2/SiOx dielectric samples on reflective metal substrates exhibited electron-induced luminescence (cathodoluminescence) under electron beam irradiation in an ultrahigh vacuum chamber at the USU facilities,. These experiments provided measurements of the absolute radiance and emission spectra as functions of incident electron energy, flux and power over a range of sample temperatures (300 K to 40 K). Early results from these experiments have led to a preliminary model of the band structure of highly disordered trapped states within the band gap of SiO2. We now extend this model to further describe the excitation of electrons from …
Charging Effects Of Multilayered Dielectric Spacecraft Materials: Surface Voltage, Discharge And Arcing, Gregory Wilson, Amberly Evans, Justin Dekany, Jr Dennison
Charging Effects Of Multilayered Dielectric Spacecraft Materials: Surface Voltage, Discharge And Arcing, Gregory Wilson, Amberly Evans, Justin Dekany, Jr Dennison
Gregory Wilson
Charging of thin-film, multilayer dielectric materials subject to electron bombardment was found to evolve with time. The charging behavior was also highly dependent on the incident energy of the monoenergetic electron beams; this is driven by energy dependant processes including the electron penetration depth, electron emission, and material conductivity. The electron penetration depth is the average range to which incident electrons at a given incident energy penetrate into the material, thus defining the mean depth of an embedded charge layer. The secondary electron yield is the ratio of electrons emitted from the surface to the number of incident electrons; this …
Novel Nanostructured Rare-Earth-Free Magnetic Materials With High Energy Products, Bhaskar Das
Novel Nanostructured Rare-Earth-Free Magnetic Materials With High Energy Products, Bhaskar Das
B. Das
Novel nanostructured Zr2Co11-based magnetic materials are fabricated in a single step process using cluster-deposition method. The composition, atomic ordering, and spin structure are precisely controlled to achieve a substantial magnetic remanence and coercivity, as well as the highest energy product for non-rare-earth and Pt-free permanent-magnet alloys.
Interaction Of Ultrashort-Laser Pulses With Induced Undercritical Plasmas In Fused Silica, Jeremy Gulley, Sebastian Winkler, William Dennis, Carl Liebig, Razvan Stoian
Interaction Of Ultrashort-Laser Pulses With Induced Undercritical Plasmas In Fused Silica, Jeremy Gulley, Sebastian Winkler, William Dennis, Carl Liebig, Razvan Stoian
Jeremy R. Gulley
Ultrafast light-material interactions near the damage threshold are often studied using postmortem analysis of damaged dielectric materials. Corresponding simulations of ultrashort pulse propagation through the material are frequently used to gain additional insight into the processes leading to such damage. However, comparison between such experimental and numerical results is often qualitative, and pulses near to but not exceeding the damage threshold leave no permanent changes in the material for postmortem analysis. In this article, a series of experiments is presented that measures the near- and far-field properties of a 140-fs laser pulse after propagation through a fused silica sample in …
Nanomagnetic Skyrmions, Ralph Skomski, Zhen Li, Rui Zhang, Roger Kirby, Axel Enders, Daniel Schmidt, T. Hofmann, Eva Schubert, David Sellmyer
Nanomagnetic Skyrmions, Ralph Skomski, Zhen Li, Rui Zhang, Roger Kirby, Axel Enders, Daniel Schmidt, T. Hofmann, Eva Schubert, David Sellmyer
Axel Enders
Magnetic skyrmions and other topologically protected nanostructures are investigated. Since skyrmions are mathematical rather than physical objects, they describe a wide variety of physical systems, from simple magnetic domain walls to complicated quantum phases with long-range many-body entanglement. Important distinctions concern the skyrmions’ relativistic character, their quantum-mechanical or classical nature, and the one- or many-body character of the wave functions. As specific examples we consider magnetic nanospirals, where the topology of a vortex-like spin state is protected by magnetostatic interactions, and edge currents in dilute magnetic semiconductors and metallic nanodots. Our analysis militates against giant orbital moments created by a …