155 research outputs found
A Method for Ultrashort Electron Pulse Shape-Measurement Using Coherent Synchrotron Radiation
In this paper we discuss a method for nondestructive measurements of the
longitudinal profile of sub-picosecond electron bunches for X-Ray Free Electron
Lasers (XFELs). The method is based on the detection of the Coherent
Synchrotron Radiation (CSR) spectrum produced by a bunch passing a dipole
magnet system. This work also contains a systematic treatment of synchrotron
radiation theory which lies at the basis of CSR. Standard theory of synchrotron
radiation uses several approximations whose applicability limits are often
forgotten: here we present a systematic discussion about these assumptions.
Properties of coherent synchrotron radiation from an electron moving along an
arc of a circle are then derived and discussed. We describe also an effective
and practical diagnostic technique based on the utilization of an
electromagnetic undulator to record the energy of the coherent radiation pulse
into the central cone. This measurement must be repeated many times with
different undulator resonant frequencies in order to reconstruct the modulus of
the bunch form-factor. The retrieval of the bunch profile function from these
data is performed by means of deconvolution techniques: for the present work we
take advantage of a constrained deconvolution method. We illustrate with
numerical examples the potential of the proposed method for electron beam
diagnostics at the TESLA Test Facility (TTF) accelerator. Here we choose, for
emphasis, experiments aimed at the measure of the strongly non-Gaussian
electron bunch profile in the TTF femtosecond-mode operation. We demonstrate
that a tandem combination of a picosecond streak camera and a CSR spectrometer
can be used to extract shape information from electron bunches with a narrow
leading peak and a long tail.Comment: 60 pages, 39 figure
Transverse self-fields within an electron bunch moving in an arc of a circle
As a consequence of motions driven by external forces, self-fields (which are
different from the static case) originate within an electron bunch. In the case
of magnetic external forces acting on an ultrarelativistic beam, the
longitudinal self-interactions are responsible for CSR (Coherent Synchrotron
Radiation)-related phenomena, which have been studied extensively. On the other
hand, transverse self-interactions are present too. At the time being, existing
theoretical analysis of transverse self-forces deal with the case of a bunch
moving along a circular orbit only, without considering the situation of a
bending magnet with a finite length. In this paper we propose an
electrodynamical analysis of transverse self-fields which originate, at the
position of a test particle, from an ultrarelativistic electron bunch moving in
an arc of a circle. The problem will be first addressed within a two-particle
system. We then extend our consideration to a line bunch with a stepped density
distribution, a situation which can be easily generalized to the case of an
arbitrary density distribution. Our approach turns out to be also useful in
order to get a better insight in the physics involved in the case of simple
circular motion and in order to address the well known issue of the partial
compensation of transverse self-force.Comment: 23 pages, 14 figure
Design and throughput simulations of a hard x-ray split and delay line for the MID station at the European XFEL
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in AIP Conference Proceedings 1741, 030010 (2016) and may be found at https://doi.org/10.1063/1.4952833.A hard X-ray Split and Delay Line (SDL) under development for the Materials Imaging and Dynamics (MID) station at the European X-Ray Free-Electron Laser (XFEL.EU) is presented. This device will provide pairs of X-ray pulses with a variable time delay ranging from â10 ps to 800 ps in a photon energy range from 5 to 10 keV. Throughput simulations in the SASE case indicate a total transmission of 1.1% or 3.5% depending on the operation mode. In the self-seeded case of XFEL.EU operation simulations indicate that the transmission can be improved to more than 11%.BMBF, 05K13KT4, Verbundprojekt FSP 302 - Freie-Elektronen-Laser: Nanoskopische Systeme. Teilprojekt 1: Split-and-Delay Instrument fĂŒr die European XFEL Beamline Materials Imaging and Dynamic
On the feasibility of a nuclear exciton laser
Nuclear excitons known from M\"ossbauer spectroscopy describe coherent
excitations of a large number of nuclei -- analogous to Dicke states (or Dicke
super-radiance) in quantum optics. In this paper, we study the possibility of
constructing a laser based on these coherent excitations. In contrast to the
free electron laser (in its usual design), such a device would be based on
stimulated emission and thus might offer certain advantages, e.g., regarding
energy-momentum accuracy. Unfortunately, inserting realistic parameters, the
window of operability is probably not open (yet) to present-day technology --
but our design should be feasible in the UV regime, for example.Comment: 7 pages RevTeX, 4 figure
VUV and X-ray coherent light with tunable polarization from single-pass free-electron lasers
Tunable polarization over a wide spectral range is a required feature of
light sources employed to investigate the properties of local symmetry in both
condensed and low-density matter. Among new-generation sources, free-electron
lasers possess a unique combination of very attractive features, as they allow
to generate powerful and coherent ultra-short optical pulses in the VUV and
X-ray spectral range. However, the question remains open about the possibility
to freely vary the light polarization of a free-electron laser, when the latter
is operated in the so-called nonlinear harmonic-generation regime. In such
configuration, one collects the harmonics of the free-electron laser
fundamental emission, gaining access to the shortest possible wavelengths the
device can generate. In this letter we provide the first experimental
characterization of the polarization of the harmonic light produced by a
free-electron laser and we demonstrate a method to obtain tunable polarization
in the VUV and X-ray spectral range. Experimental results are successfully
compared to those obtained using a theoretical model based on the paraxial
solution of Maxwell's equations. Our findings can be expected to have a deep
impact on the design and realization of experiments requiring full control of
light polarization to explore the symmetry properties of matter samples
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
Volt-per-Ă ngstrom terahertz fields from X-ray free-electron lasers
The electron linear accelerators driving modern X-ray free-electron lasers can emit intense, tunable, quasi-monochromatic terahertz (THz) transients with peak electric fields of V Ă
â»Âč and peak magnetic fields in excess of 10 T when a purpose-built, compact, superconducting THz undulator is implemented. New research avenues such as X-ray movies of THz-driven mode-selective chemistry come into reach by making dual use of the ultra-short GeV electron bunches, possible by a rather minor extension of the infrastructure
Single-shot transverse coherence in seeded and unseeded free-electron lasers: A comparison
The advent of x-ray free-electron lasers (FELs) drastically enhanced the capabilities of several analytical techniques, for which the degree of transverse (spatial) coherence of the source is essential. FELs can be operated in self-amplified spontaneous emission (SASE) or seeded configurations, which rely on a qualitatively different initialization of the amplification process leading to light emission. The degree of transverse coherence of SASE and seeded FELs has been characterized in the past, both experimentally and theoretically. However, a direct experimental comparison between the two regimes in similar operating conditions is missing, as well as an accurate study of the sensitivity of transverse coherence to key working parameters. In this paper, we carry out such a comparison, focusing in particular on the evolution of coherence during the light amplification process
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