151 research outputs found
Scanning Electron Microscopy Observation of the Voltage Contrast Image of the Ferroelectric Domain Structure in the LiNbO3 Crystal
This paper reports a scanning electron microscopy study of the formation of the voltage contrast image of the ferroelectric domain structure in the LiNbO3 crystal. We investigated the formation of the pyroelectric voltage contrast image of the regular domain structure. For our experiment, we used ZY cut of a LiNbO3 crystal which had a regular domain structure with a domain width of -55 μm. The regular domain structure in the LiNbO3 crystal was formed by the method of thermo-electrical treatment after growth. The pyroelectric voltage contrast image of the regular domain structure in the scanning electron microscope was formed by applying the pyroelectric effect along polar axis Z. The difference in the voltage contrast in the neighboring domains connect with opposite directions of polar axis Z in the neighboring domains. It is shown that the voltage contrast of the ferroelectric domain structures is defined by the physical properties and orientation of the ferroelectric crystals
Correlated two-photon emission by transitions of Dirac-Volkov states in intense laser fields: QED predictions
In an intense laser field, an electron may decay by emitting a pair of
photons. The two photons emitted during the process, which can be interpreted
as a laser-dressed double Compton scattering, remain entangled in a
quantifiable way: namely, the so-called concurrence of the photon polarizations
gives a gauge-invariant measure of the correlation of the hard gamma rays. We
calculate the differential rate and concurrence for a backscattering setup of
the electron and photon beam, employing Volkov states and propagators for the
electron lines, thus accounting nonperturbatively for the electron-laser
interaction. The nonperturbative results are shown to differ significantly
compared to those obtained from the usual double Compton scattering.Comment: 32 pages, 12 figure
Muon pair creation from positronium in a circularly polarized laser field
We study elementary particle reactions that result from the interaction of an
atomic system with a very intense laser wave of circular polarization. As a
specific example, we calculate the rate for the laser-driven reaction , where the electron and positron originate from a positronium
atom or, alternatively, from a nonrelativistic plasma. We distinguish
accordingly between the coherent and incoherent channels of the process. Apart
from numerical calculations, we derive by analytical means compact formulas for
the corresponding reaction rates. The rate for the coherent channel in a laser
field of circular polarization is shown to be damped because of the destructive
interference of the partial waves that constitute the positronium ground-state
wave packet. Conditions for the observation of the process via the dominant
incoherent channel in a circularly polarized field are pointed out
Scanning Electron Microscopy Observation of the Interaction Between the Surface Acoustic Waves and Regular Domain Structures in the LiNbO3 Crystals
This paper reports a scanning electron microscope study of the interaction between the surface acoustic waves and regular domain structures in LiNbO3 crystals. The regular domain structures in LiNbO3 crystals were formed by the method of the thermo-electric treatment after growth. We investigated two modes of interaction: the surface-acoustic-waves propagate along and across the regular domain structures. It is shown that the regular domain structures in the first case can be used as an acoustical wave-guide, because the power-flow vector of the surface acoustic waves has the direction along the domain structure. Also we observed that the surface acoustic wave inverts the voltage contrast of the image in the scanning electron microscope by π during the process of the propagation across the domain walls
Surface acoustic wave propagation in graphene film
Surface acoustic wave (SAW) propagation in a graphene film on the surface of piezoelectric crystals was studied at the BESSY II synchrotron radiation source. Talbot effect enabled the visualization of the SAW propagation on the crystal surface with the graphene film in a real time mode, and high-resolution x-ray diffraction permitted the determination of the SAW amplitude in the graphene/piezoelectric crystal system. The influence of the SAW on the electrical properties of the graphene film was examined. It was shown that the changing of the SAW amplitude enables controlling the magnitude and direction of current in graphene film on the surface of piezoelectric crystals
Breit-Wheeler Process in Intense Short Laser Pulses
Energy-angular distributions of electron-positron pair creation in collisions
of a laser beam and a nonlaser photon are calculated using the -matrix
formalism. The laser field is modeled as a finite pulse, similar to the
formulation introduced in our recent paper in the context of Compton scattering
[Phys. Rev. A {\bf 85}, 062102 (2012)]. The nonperturbative regime of pair
creation is considered here. The energy spectra of created particles are
compared with the corresponding spectra obtained using the modulated plane wave
approximation for the driving laser field. A very good agreement in these two
cases is observed, provided that the laser pulse is sufficiently long. For
short pulse durations, this agreement breaks down. The sensitivity of pair
production to the polarization of a driving pulse is also investigated. We show
that in the nonperturbative regime, the pair creation yields depend on the
polarization of the pulse, reaching their maximal values for the linear
polarization. Therefore, we focus on this case. Specifically, we analyze the
dependence of pair creation on the relative configuration of linear
polarizations of the laser pulse and the nonlaser photon. Lastly, we
investigate the carrier-envelope phase effect on angular distributions of
created particles, suggesting the possibility of phase control in relation to
the pair creation processes.Comment: 13 pages, 8 figure
Caustic structures in the spectrum of x-ray Compton scattering off electrons driven by a short intense laser pulse
We study the Compton scattering of x-rays off electrons that are driven by a
relativistically intense short optical laser pulse. The frequency spectrum of
the laser-assisted Compton radiation shows a broad plateau in the vicinity of
the laser-free Compton line due to a nonlinear mixing between x-ray and laser
photons. Special emphasis is placed on how the shape of the short assisting
laser pulse affects the spectrum of the scattered x-rays. In particular, we
observe sharp peak structures in the plateau region, whose number and locations
are highly sensitive to the laser pulse shape. These structures are interpreted
as spectral caustics by using a semiclassical analysis of the laser-assisted
QED matrix element
ФОРМИРОВАНИЕ СЕГНЕТОЭЛЕКТРИЧЕСКИХ ДОМЕННЫХ СТРУКТУР В КРИСТАЛЛАХ LiTaO3 МЕТОДОМ ПРЯМОЙ ЭЛЕКТРОННО–ЛУЧЕВОЙ ПЕРЕПОЛЯРИЗАЦИИ
The process of repolarization of a LiTaO3 crystal by e−beam lithography was studied. The process of fabrication of ferroelectric domains with domain width of 1 μm was demonstrated. It was shown that in the 127° Y¢-cut of a ferroelectric LiTaO3 crystal the ferroelectric domains is formed at the angle of 37° the crystal surface and growth along polar axis Z from negative surface to positive surface Z.Исследован процесс переполяризации сегнетоэлектрического кристалла LiTaO3 методом прямой электронно-лучевой литографии. Продемонстрирована возможность формирования доменной структуры с шириной доменнов ~1 мкм. Показано, что в 127° Y'-срезе кристалла LiTaO3 сегнетоэлектрические домены формируются под углом 37° к поверхности кристалла и растут от отрицательной поверхности к положительной вдоль полярной оси Z
- …