203 research outputs found
Formation of Luminescence Centers in Oxygen-Deficient Cerium Oxide Nanocrystals
In this work the peculiarities of oxygen vacancies formation in cerium oxide nanoparticles for different
external influences have been investigated by spectroscopic methods.
The features of oxygen vacancies and therefore non-stoichiometric cerium oxide formation in CeO2
nanocrystals depending on the atmosphere of high temperature treatment were investigated. Stimulation
of oxygen vacancies formation in reducing and neutral atmospheres was revealed. Occurrence of two different
luminescence centers (viz. the charge-transfer complexes formed by Ce4+ and O2- ions, and Ce3+ ions
stabilized by vacancies) after cerium oxide nanoparticles annealing in a neutral atmosphere has been observed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3544
Acceleration of electrons in a self-modulated laser wakefield
Acceleration of electrons in a self-modulated laser-wakefield is investigated. The generated electron beam is oberved to have a multi-component beam profile and its energy distribution undergoes discrete transitions as the conditions are varied. These features can be explained by simple simulations of electron propagation in a 3-D plasma wave. Ā© 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87719/2/333_1.pd
Electron acceleration by self-modulated laser wakefield in a relativistically self-guided channel
The relativistic self-focusing of an intense laser pulse (I ā¼ 4Ć1018āW/cm2,Iā¼4Ć1018W/cm2, Ī» = 1āĪ¼m,Ī»=1Ī¼m, Ļ = 400āfsĻ=400fs) in a gas jet 750 Ī¼m in length was observed using sidescattering imaging. A self-modulated laser wakefield was generated to accelerate self-trapped electrons. The energy distribution and transverse emittance of the electron beam changed due to the onset of the relativistic self-guiding. Ā© 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87563/2/408_1.pd
Relativistic spherical plasma waves
Tightly focused laser pulses as they diverge or converge in underdense plasma
can generate wake waves, having local structures that are spherical waves. Here
we report on theoretical study of relativistic spherical wake waves and their
properties, including wave breaking. These waves may be suitable as particle
injectors or as flying mirrors that both reflect and focus radiation, enabling
unique X-ray sources and nonlinear QED phenomena.Comment: 6 pages; 4 figure
High Flux Femtosecond X-ray Emission from the Electron-Hose Instability in Laser Wakefield Accelerators
Bright and ultrashort duration X-ray pulses can be produced by through
betatron oscillations of electrons during Laser Wakefield Acceleration (LWFA).
Our experimental measurements using the \textsc{Hercules} laser system
demonstrate a dramatic increase in X-ray flux for interaction distances beyond
the depletion/dephasing lengths, where the initial electron bunch injected into
the first wake bucket catches up with the laser pulse front and the laser pulse
depletes. A transition from an LWFA regime to a beam-driven plasma wakefield
acceleration (PWFA) regime consequently occurs. The drive electron bunch is
susceptible to the electron-hose instability and rapidly develops large
amplitude oscillations in its tail, which leads to greatly enhanced X-ray
radiation emission. We measure the X-ray flux as a function of acceleration
length using a variable length gas cell. 3D particle-in-cell (PIC) simulations
using a Monte Carlo synchrotron X-ray emission algorithm elucidate the
time-dependent variations in the radiation emission processes.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev. Accel.
Beam
Nonlinear optics in relativistic plasmas
We discuss various nonlinear optical processes that occur as an intense laser propagates through a relativistic plasma. These include the experimental observations of electron acceleration driven by laser-wakefield generation, relativistic self-focusing, waveguide formation and laser self-channeling. Ā© 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87450/2/103_1.pd
Mechanism and Control of HighāIntensityāLaserāDriven Proton Acceleration
We discuss the optimization and control of laserādriven proton beams. Specifically, we report on the dependence of highāintensity laser accelerated proton beams on the material properties of various thināfilm targets. Evidence of starālike filaments and beam hollowing (predicted from the electrothermal instability theory) is observed on Radiochromic Film (RCF) and CRā39 nuclear track detectors. The proton beam spatial profile is found to depend on initial target conductivity and target thickness. For resistive target materials, these structured profiles are explained by the inhibition of current, due to the lack of a return current. The conductors, however, can support large propagating currents due to the substantial cold return current which is composed of free charge carriers in the conduction band to neutralize the plasma from the interaction. The empirical plot shows relationship between the maximum proton energy and the target thickness also supports the return current and target normal sheath acceleration (TNSA) theory. We have also observed filamentary structures in the proton beam like those expected from the Weibel instability in the electron beam. Along with the ion acceleration, a clear electron beam is detected by the RCF along the tangent to the target, which is also the surface direction of target plate. Ā© 2004 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87542/2/595_1.pd
High harmonic generation in relativistic laserāplasma interaction
High harmonics generated due to the scattering of relativistic electrons from high intensity laser light is studied. The experiments are carried out with an Nd:Glass laser system with a peak intensity of 2Ć1018āWācmā22Ć1018Wcmā2 in underdense plasma. It is shown that, at high intensities, when the normalized electric field approaches unity, in addition to the conventional atomic harmonics from bound electrons there is significant contribution to the harmonic spectrum from free electrons. The characteristic signatures of this are found to be the emission of even order harmonics, linear dependence on the electron density, significant amount of harmonics even with circular polarization and a much smaller spatial region over which these harmonics are produced as compared to the atomic case. Imaging of the harmonic beam shows that it is emitted in a narrow cone with a divergence of 2 to 3 degrees. Ā© 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70961/2/PHPAEN-9-5-2393-1.pd
Control of Bright Picosecond X-Ray Emission from Intense Subpicosecond Laser-Plasma Interactions
Using temporally and spectrally resolved diagnostics, we show that the pulse duration of laser-produced soft x rays emitted from solid targets can be controlled, permitting a reduction to as short as a few picoseconds. To enable this control, only a single parameter must be adjusted, namely, the intensity of the high-contrast ultrashort laser pulse (400 fs). These results are found to be in qualitative agreement with a simple model of radiation from a collisionally dominated atomic system
Temporal characterization of a self-modulated laser wakefield
The temporal envelope of plasma density oscillations in the wake of an intense (I ā¼ 4Ć1018āW/cm2,Iā¼4Ć1018W/cm2, Ī» = 1āĪ¼mĪ»=1Ī¼m) laser pulse (400 fs) is measured using forward Thomson scattering from a copropagating, frequency doubled probe pulse. The wakefield oscillations in a fully ionized helium plasma (ne = 3Ć1019ācmā3)(ne=3Ć1019cmā3) are observed to reach maximum amplitude (Ī“ne/ne ā¼ 0.1)(Ī“ne/neā¼0.1) 300 fs after the pump pulse. The wakefield growth (4āpsā1)(4psā1) and decay (1.9āpsā1)(1.9psā1) rates are consistent with the forward Raman scattering instability and beam loading, respectively. Ā© 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87567/2/651_1.pd
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