979 research outputs found
Effect of a strong laser field on photoproduction by relativistic nuclei
We study the influence of a strong laser field on the Bethe-Heitler
photoproduction process by a relativistic nucleus. The laser field propagates
in the same direction as the incoming high-energy photon and it is taken into
account exactly in the calculations. Two cases are considered in detail. In the
first case, the energy of the incoming photon in the nucleus rest frame is much
larger than the electron's rest energy. The presence of the laser field may
significantly suppress the photoproduction rate at soon available values of
laser parameters. In the second case, the energy of the incoming photon in the
rest frame of the nucleus is less than and close to the electron-positron pair
production threshold. The presence of the laser field allows for the pair
production process and the obtained electron-positron rate is much larger than
in the presence of only the laser and the nuclear field. In both cases we have
observed a strong dependence of the rate on the mutual polarization of the
laser field and of the high-energy photon and the most favorable configuration
is with laser field and high-energy photon linearly polarized in the same
direction. The effects discussed are in principle measurable with presently
available proton accelerators and laser systems.Comment: 21 pages, 4 figure
Feasibility of electron cyclotron autoresonance acceleration by a short terahertz pulse
A vacuum autoresonance accelerator scheme for electrons, which employs
terahertz radiation and currently available magnetic fields, is suggested.
Based on numerical simulations, parameter values, which could make the scheme
experimentally feasible, are identified and discussed
Polarization operator approach to electron-positron pair production in combined laser and Coulomb fields
The optical theorem is applied to the process of electron-positron pair
creation in the superposition of a nuclear Coulomb and a strong laser field. We
derive new representations for the total production rate as two-fold integrals,
both for circular laser polarization and for the general case of elliptic
polarization, which has not been treated before. Our approach allows us to
obtain by analytical means the asymptotic behaviour of the pair creation rate
for various limits of interest. In particular, we consider pair production by
two-photon absorption and show that, close to the energetic threshold of this
process, the rate obeys a power law in the laser frequency with different
exponents for linear and circular laser polarization. With the help of the
upcoming x-ray laser sources our results could be tested experimentally.Comment: 10 pages, 3 figure
High-quality multi-GeV electron bunches via cyclotron autoresonance
Autoresonance laser acceleration of electrons is theoretically investigated
using circularly polarized focused Gaussian pulses. Many-particle simulations
demonstrate feasibility of creating over 10-GeV electron bunches of ultra-high
quality (relative energy spread of order 10^-4), suitable for fundamental
high-energy particle physics research. The laser peak intensities and axial
magnetic field strengths required are up to about 10^18 W/cm^2 (peak power ~10
PW) and 60 T, respectively. Gains exceeding 100 GeV are shown to be possible
when weakly focused pulses from a 200-PW laser facility are used
Analytic model of a multi-electron atom
A fully analytical approximation for the observable characteristics of many-electron atoms is developed via a complete and orthonormal hydrogen-like basis with a single-effective charge parameter for all electrons of a given atom. The basis completeness allows us to employ the secondary-quantized representation for the construction of regular perturbation theory, which includes in a natural way correlation effects, converges fast and enables an effective calculation of the subsequent corrections. The hydrogen-like basis set provides a possibility to perform all summations over intermediate states in closed form, including both the discrete and continuous spectra. This is achieved with the help of the decomposition of the multi-particle Green function in a convolution of single-electronic Coulomb Green functions. We demonstrate that our fully analytical zeroth-order approximation describes the whole spectrum of the system, provides accuracy, which is independent of the number of electrons and is important for applications where the Thomas-Fermi model is still utilized. In addition already in second-order perturbation theory our results become comparable with those via a multi-configuration Hartree-Fock approach
Parametric Mössbauer radiation source
Numerous applications of Mossbauer spectroscopy are related to a unique resolution of absorption spectra of resonant radiation in crystals, when the nucleus absorbs a photon without a recoil. However, the narrow nuclear linewidth renders efficient driving of the nuclei challenging, restricting precision spectroscopy, nuclear inelastic scattering and nuclear quantum optics. Moreover, the need for dedicated x-ray optics restricts access to only few isotopes, impeding precision spectroscopy of a wider class of systems. Here, we put forward a novel Mossbauer source, which offers resonant photon flux for a large variety of Mossbauer isotopes with strongly suppressed electronic background. It is based on relativistic electrons moving through a crystal and emitting parametric Mossbauer radiation essentially unattenuated by electronic absorption. As a result, a collimated beam of resonant photons is formed, without the need for additional monochromatization. We envision the extension of high-precision Mossbauer spectroscopy to a wide range of isotopes at accelerator facilities, also using dumped electron beams
Light diffraction by a strong standing electromagnetic wave
The nonlinear quantum interaction of a linearly polarized x-ray probe beam
with a focused intense standing laser wave is studied theoretically. Because of
the tight focusing of the standing laser pulse, diffraction effects arise for
the probe beam as opposed to the corresponding plane wave scenario. A
quantitative estimate for realistic experimental conditions of the ellipticity
and the rotation of the main polarization plane acquired by the x-ray probe
after the interaction shows that the implementation of such vacuum effects is
feasible with future X-ray Free Electron Laser light.Comment: 5 pages, 2 figures. Published versio
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