404 research outputs found
Parametric frequency mixing in the magneto-elastically driven FMR-oscillator
We demonstrate the nonlinear frequency conversion of ferromagnetic resonance
(FMR) frequency by optically excited elastic waves in a thin metallic film on
dielectric substrates. Time-resolved probing of the magnetization directly
witnesses magneto-elastically driven second harmonic generation, sum- and
difference frequency mixing from two distinct frequencies, as well as
parametric downconversion of each individual drive frequency. Starting from the
Landau-Lifshitz-Gilbert equations, we derive an analytical equation of an
elastically driven nonlinear parametric oscillator and show that frequency
mixing is dominated by the parametric modulation of FMR frequency
Structural and Magnetic Characterization of Large Area, Free-Standing Thin Films of Magnetic Ion Intercalated Dichalcogenides Mn0.25TaS2 and Fe0.25TaS2
Free-standing thin films of magnetic ion intercalated transition metal
dichalcogenides are produced using ultramicrotoming techniques. Films of
thicknesses ranging from 30nm to 250nm were achieved and characterized using
transmission electron diffraction and X-ray magnetic circular dichroism.
Diffraction measurements visualize the long range crystallographic ordering of
the intercalated ions, while the dichroism measurements directly assess the
orbital contributions to the total magnetic moment. We thus verify the
unquenched orbital moment in Fe0.25TaS2 and measure the fully quenched orbital
contribution in Mn0.25TaS2. Such films can be used in a wide variety of
ultrafast X-ray and electron techniques that benefit from transmission
geometries, and allow measurements of ultrafast structural, electronic, and
magnetization dynamics in space and time
Dilated intercellular spaces: A morphological feature of acid reflux-- damaged human esophageal epithelium
AbstractBACKGROUND & AIMS: Dilated intercellular spaces are a sign of epithelial damage in acid-perfused rabbit esophagus, a change best identified by transmission electron microscopy. The aim of this study was to determine if this change is also a feature of acid damage to human esophageal epithelium. METHODS: Endoscopic esophageal biopsy specimens from patients with (n = 11) and without (n = 13) recurrent heartburn were examined using transmission electron microscopy. Of 11 patients with heartburn, 6 had erosive esophagitis and 5 had normal- appearing mucosa on endoscopy; 13 controls had no symptoms or signs of esophageal disease. Using a computer, intercellular space diameter was measured from transmission electron microscopy photomicrographs of the specimen from each patient. RESULTS: Intercellular space diameter was significantly greater in specimens from patients with heartburn than those from controls; this was true irrespective of whether the patient had erosive or nonerosive disease. Space diameters of > or=2.4 microns were present in 8 of 11 patients with heartburn and in no controls. CONCLUSIONS: Dilated intercellular spaces are a feature of reflux damage to human esophageal epithelium. As a morphological marker of increased paracellular permeability, its presence in patients without endoscopic abnormalities may help explain their development of heartburn. (Gastroenterology 1996 Nov;111(5):1200-5
Quasi-phase-matched generation of coherent extreme-ultraviolet light
Includes bibliographical references (page 54).High-harmonic generation is a well-known method of producing coherent extreme-ultraviolet (EUV) light, with photon energies up to about 0.5 keV. This is achieved by focusing a femtosecond laser into a gas, and high harmonics of the fundamental laser frequency are radiated in the forward direction. However, although this process can generate high-energy photons, efficient high-harmonic generation has been demonstrated only for photon energies of the order 50-100 eV. Ionization of the gas prevents the laser and the EUV light from propagating at the same speed, which severely limits the conversion efficiency. Here we report a technique to overcome this problem, and demonstrate quasi-phase-matched frequency conversion of laser light into EUV. Using a modulated hollow-core waveguide to periodically vary the intensity of the laser light driving the conversion, we efficiently generate EUV light even in the presence of substantial ionization. The use of a modulated fibre shifts the energy spectrum of the high-harmonic light to significantly higher photon energies than would otherwise be possible. We expect that this technique could form the basis of coherent EUV sources for advanced lithography and high-resolution imaging applications. In future work, it might also be possible to generate isolated attosecond pulses
Evidence for a three-nucleon-force effect in proton-deuteron elastic scattering
Developments in spin-polarized internal targets for storage rings have
permitted measurements of 197 MeV polarized protons scattering from vector
polarized deuterons. This work presents measurements of the polarization
observables A_y, iT_11, and C_y,y in proton-deuteron elastic scattering. When
compared to calculations with and without three-nucleon forces, the
measurements indicate that three-nucleon forces make a significant contribution
to the observables. This work indicates that three-body forces derived from
static nuclear properties appear to be crucial to the description of dynamical
properties.Comment: 8 pages 2 figures Latex, submitted to Phys. Rev. Letter
XUV digital in-line holography using high-order harmonics
A step towards a successful implementation of timeresolved digital in-line
holography with extreme ultraviolet radiation is presented. Ultrashort XUV
pulses are produced as high-order harmonics of a femtosecond laser and a
Schwarzschild objective is used to focus harmonic radiation at 38 nm and to
produce a strongly divergent reference beam for holographic recording.
Experimental holograms of thin wires are recorded and the objects
reconstructed. Descriptions of the simulation and reconstruction theory and
algorithms are also given. Spatial resolution of few hundreds of nm is
potentially achievable, and micrometer resolution range is demonstrated.Comment: 8 pages, 8 figure
Driving Magnetization Dynamics in an On-Demand Magnonic Crystal via the Magnetoelastic Interactions
Using spatial light interference of ultrafast laser pulses, we generate a lateral modulation in the magnetization profile of an otherwise uniformly magnetized film, whose magnetic excitation spectrum is monitored via the coherent and resonant interaction with elastic waves. We find an unusual dependence of the magnetoelastic coupling as the externally applied magnetic field is angle- and field-tuned relative to the wave vector of the magnetization modulation, which can be explained by the emergence of spatially inhomogeneous spin-wave modes. In this regard, the spatial light interference methodology can be seen as a user-configurable, temporally windowed, on-demand magnonic crystal, potentially of arbitrary two-dimensional shape, which allows control and selectivity of the spatial distribution of spin waves. Calculations of spin waves using a variety of methods, demonstrated here using the plane-wave method and micromagnetic simulation, can identify the spatial distribution and associated energy scales of each excitation, which opens the door to a number of excitation methodologies beyond our chosen elastic wave excitation
Impact of Environmental Regulations on Trade in the Main EU Countries: Conflict or Synergy?
Transient Grating Spectroscopy in Magnetic Thin Films:Simultaneous Detection of Elastic and Magnetic Dynamics
Surface magnetoelastic waves are coupled elastic and magnetic excitations that propagate along the surface of a magnetic material. Ultrafast optical techniques allow for a non-contact excitation and detection scheme while providing the ability to measure both elastic and magnetic components individually. Here we describe a simple setup suitable for excitation and time resolved measurements of high frequency magnetoelastic waves, which is based on the transient grating technique. The elastic dynamics are measured by diffracting a probe laser pulse from the long-wavelength spatially periodic structural deformation. Simultaneously, a magnetooptical measurement, either Faraday or Kerr effect, is sensitive to the out-of-plane magnetization component. The correspondence in the response of the two channels probes the resonant interaction between the two degrees of freedom and reveals their intimate coupling. Unraveling the observed dynamics requires a detailed understanding of the spatio-temporal evolution of temperature, magnetization and thermo-elastic strain in the ferromagnet. Numerical solution of thermal diffusion in two dimensions provides the basis on which to understand the sensitivity in the magnetooptic detection
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