469 research outputs found
Fel Oscillators with Tapered Undulators: Inclusion of Harmonic Generation and Pulse Propagation
We review the theory of FEL oscillators operating with tapered undulators. We
consider the case of a uniform tapering and introduce a parameter which
characterizes the effect of the tapering on the gain and on the saturation
intensity. We analyze the effect of the tapering on the FEL dynamics by
including the pulse propagation effects too. We analyze the importance of
tapering as a tool to model the optical pulse shapes and to control the higher
harmonic intensities
On Free-Electron Laser Growing Modes and their Bandwidth
Free-electron lasers play an increasing role in science, from generating
unique femtosecond X- ray pulses for single short recording of the protein
structures to amplifying feeble interactions in advanced cooling systems for
high-energy hadron colliders. While modern Free-electron laser codes can
describe their amplification mechanism, a deep analytical understanding of the
mechanism is of extreme importance for a number of applications. Mode
competition, their growth rates and amplification bandwidth are among the most
important parameters of a free-electron laser. A dispersion relation, which
defines these important characteristics, can be solved analytically only for a
very few simple cases. In this letter we show that for a typical bell-shape
energy distribution in electron beam there is no more that one growing mode. We
also derive an analytical expression which determines the bandwidth of the
free-electron laser.Comment: 4 pages, submitted to PR
Manifestation of quantum chaos on scattering techniques: application to low-energy and photo-electron diffraction intensities
Intensities of LEED and PED are analyzed from a statistical point of view.
The probability distribution is compared with a Porter-Thomas law,
characteristic of a chaotic quantum system. The agreement obtained is
understood in terms of analogies between simple models and Berry's conjecture
for a typical wavefunction of a chaotic system. The consequences of this
behaviour on surface structural analysis are qualitatively discussed by looking
at the behaviour of standard correlation factors.Comment: 5 pages, 4 postscript figures, Latex, APS,
http://www.icmm.csic.es/Pandres/pedro.ht
Optical Klystron Enhancement to SASE X-ray FELs
The optical klystron enhancement to self-amplified spontaneous emission
(SASE) free electron lasers (FELs) is studied in theory and in simulations. In
contrast to a seeded FEL, the optical klystron gain in a SASE FEL is not
sensitive to any phase mismatch between the radiation and the microbunched
electron beam. The FEL performance with the addition of four optical klystrons
located at the undulator long breaks in the Linac Coherent Light Source (LCLS)
shows significant improvement if the uncorrelated energy spread at the
undulator entrance can be controlled to a very small level. In addition, FEL
saturation at shorter x-ray wavelengths (around 1.0 \AA) within the LCLS
undulator length becomes possible. We also discuss the application of the
optical klystron in a compact x-ray FEL design that employs relatively low
electron beam energy together with a short-period undulator.Comment: 17 pages, 8 figures, submitted to Phys. Rev. ST Accel. Beam
Cooperative effects in nuclear excitation with coherent x-ray light
The interaction between super-intense coherent x-ray light and nuclei is
studied theoretically. One of the main difficulties with driving nuclear
transitions arises from the very narrow nuclear excited state widths which
limit the coupling between laser and nuclei. In the context of direct
laser-nucleus interaction, we consider the nuclear width broadening that occurs
when in solid targets, the excitation caused by a single photon is shared by a
large number of nuclei, forming a collective excited state. Our results show
that for certain isotopes, cooperative effects may lead to an enhancement of
the nuclear excited state population by almost two orders of magnitude.
Additionally, an update of previous estimates for nuclear excited state
population and signal photons taking into account the experimental advances of
the x-ray coherent light sources is given. The presented values are an
improvement by orders of magnitude and are encouraging for the future prospects
of nuclear quantum optics.Comment: 22 pages, 4 figures, 5 tables; updated to the published version, one
additional results tabl
Calculation of the Coherent Synchrotron Radiation Impedance from a Wiggler
Most studies of Coherent Synchrotron Radiation (CSR) have only considered the
radiation from independent dipole magnets. However, in the damping rings of
future linear colliders, a large fraction of the radiation power will be
emitted in damping wigglers. In this paper, the longitudinal wakefield and
impedance due to CSR in a wiggler are derived in the limit of a large wiggler
parameter . After an appropriate scaling, the results can be expressed in
terms of universal functions, which are independent of . Analytical
asymptotic results are obtained for the wakefield in the limit of large and
small distances, and for the impedance in the limit of small and high
frequencies.Comment: 10 pages, 8 figure
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