3,293 research outputs found
Photon emission by ultra-relativistic positrons in crystalline undulators: the high-energy regime
This paper discusses the undulator radiation emitted by high-energy positrons
during planar channeling in periodically bent crystals. We demonstrate that the
construction of the undulator for positrons with energies of 10 GeV and above
is only possible if one takes into account the radiative energy losses. The
frequency of the undulator radiation depends on the energy of the particle.
Thus the decrease of the particle's energy during the passage of the crystal
should result in the destruction of the undulator radiation regime. However, we
demonstrate that it is possible to avoid the destructive influence of the
radiative losses on the frequency of the undulator radiation by the appropriate
variation of the shape of the crystal channels. We also discuss a method by
which, to our mind, it would be possible to prepare the crystal with the
desired properties of its channels.Comment: submitted for the proceedings of the International Workshop on
``Electron-Photon Interaction in Dense Media'' in Nor-Hamberd, Armenia, 2001;
10 pages, 9 figures, LaTe
Spontaneous and stimulated undulator radiation by an ultra-relativistic positron channeling in a periodically bent crystal
We discuss the radiation generated by positrons channeling in a crystalline
undulator. The undulator is produced by periodically bending a single crystal
with an amplitude much larger than the interplanar spacing. Different
approaches for bending the crystal are described and the restrictions on the
parameters of the bending are discussed. We also present numeric calculations
of the spontaneous emitted radiation and estimate the conditions for stimulated
emission. Our investigations show that the proposed mechanism could be an
interesting source for high energy photons and is worth to be studied
experimentally.Comment: long version of our contribution to the 22nd International Free
Electron Laser Conference, Durham, NC, USA, 13-18 August 2000, Reprinted from
Nuclear Instruments and Methods A, Volume 474, 1--3, in press, with
permission from Elsevier Science. http://www.elsevier.com/locate/nim
Channeling of Charged Particles Through Periodically Bent Crystals: on the Possibility of a Gamma Laser
We discuss radiation generated by positrons channeling in a crystalline
undulator. The undulator is produced by periodically bending a single crystal
with an amplitude much larger than the interplanar spacing. Different
approaches for bending the crystal are described and the restrictions on the
parameters of the bending are established. We present the results of numeric
calculations of the spectral distributions of the spontaneous emitted radiation
and estimate the conditions for stimulated emission. Our investigations show
that the proposed mechanism provides an efficient source for high energy
photons, which is worth to be studied experimentally.Comment: contributed to the conference ``Fundamental and Applied Aspects of
Modern Physics'' in Luederitz, Namibia, 200
Total energy losses due to the radiation in an acoustically based undulator: the undulator and the channeling radiation included
This paper is devoted to the investigation of the radiation energy losses of
an ultra-relativistic charged particle channeling along a crystal plane which
is periodically bent by a transverse acoustic wave. In such a system there are
two essential mechanisms leading to the photon emission. The first one is the
ordinary channeling radiation. This radiation is generated as a result of the
transverse oscillatory motion of the particle in the channel. The second one is
the acoustically induced radiation. This radiation is emitted because of the
periodic bending of the particle's trajectory created by the acoustic wave. The
general formalism described in our work is applicable for the calculation of
the total radiative losses accounting for the contributions of both radiation
mechanisms. We analyze the relative importance of the two mechanisms at various
amplitudes and lengths of the acoustic wave and the energy of the projectile
particle. We establish the ranges of projectile particle energies, in which
total energy loss is small for the LiH, C, Si, Ge, Fe and W crystals. This
result is important for the determination of the projectile particle energy
region, in which acoustically induced radiation of the undulator type and also
the stimulated photon emission can be effectively generated. The latter effects
have been described in our previous works
Electron-based crystalline undulator
We discuss the features of a crystalline undulator of the novel type based on
the effect of a planar channeling of ultra-relativistic electrons in a
periodically bent crystals. It is demonstrated that an electron-based undulator
is feasible in the tens of GeV range of the beam energies, which is noticeably
higher than the energy interval allowed in a positron-based undulator.
Numerical analysis of the main parameters of the undulator as well as the
characteristics of the emitted undulator radiation is carried out for 20 and 50
GeV electrons channeling in diamond and silicon crystals along the (111)
crystallographic planes.Comment: 16 pages, 8 figures, Latex, IOP styl
Coherent radiation of an ultra-relativistic charged particle channeled in a periodically bent crystal
We suggest a new type of the undulator radiation which is generated by an
ultra-relativistic particle channeled along a periodically bent
crystallographic plane or axis. The electromagnetic radiation arises mainly due
to the bending of the particle's trajectory, which follows the shape of the
channel. The parameters of this undulator, which totally define the spectrum
and the angular distribution of the radiation (both spontaneous and
stimulated), depend on the type of the crystal and the crystallographic plane
(axis), on the type of a projectile and its energy, and on the shape of the
bent channel, and, thus, can be varied significantly by varying these
characteristics.
As an example, we consider the acoustically induced radiation (AIR) which is
generated by ultra-relativistic particles channeled in a crystal which is bent
by a transverse acoustic wave. The AIR mechanism allows to make the undulator
with the main parameters varying in wide ranges, which are inaccessible in the
undulators based on the motion of particles in the periodic magnetic fields and
also in the field of the laser radiation. The intensity of AIR can be easily
made larger than the intensity of the radiation in a linear crystal and can be
varied in a wide range by varying the frequency and the amplitude of the
acoustic wave in the crystal. A possibility to generate stimulated emission of
high-energy photons (in keV - MeV region) is also discussed.Comment: published in J. Phys. G: Nucl. Part. Phys. 24 (1998) L45-L53,
http://www.iop.or
Three-photon detachment of electrons from the fluorine negative ion
Absolute three-photon detachment cross sections are calculated for the
fluorine negative ion within the lowest-order perturbation theory. The Dyson
equation of the atomic many-body theory is used to obtain the ground-state 2p
wavefunction with correct asymptotic behaviour, corresponding to the true
(experimental) binding energy. We show that in accordance with the adiabatic
theory (Gribakin and Kuchiev 1997 {Phys. Rev. A} {\bf 55} 3760) this is crucial
for obtaining absolute values of the multiphoton cross sections. Comparisons
with other calculations and experimental data are presented.Comment: 10 pages, two figures, Latex, IOP styl
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