470 research outputs found
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
Delayed Self-Synchronization in Homoclinic Chaos
The chaotic spike train of a homoclinic dynamical system is self-synchronized
by re-inserting a small fraction of the delayed output. Due to the sensitive
nature of the homoclinic chaos to external perturbations, stabilization of very
long periodic orbits is possible. On these orbits, the dynamics appears chaotic
over a finite time, but then it repeats with a recurrence time that is slightly
longer than the delay time. The effect, called delayed self-synchronization
(DSS), displays analogies with neurodynamic events which occur in the build-up
of long term memories.Comment: Submitted to Phys. Rev. Lett., 13 pages, 7 figure
A propensity criterion for networking in an array of coupled chaotic systems
We examine the mutual synchronization of a one dimensional chain of chaotic
identical objects in the presence of a stimulus applied to the first site. We
first describe the characteristics of the local elements, and then the process
whereby a global nontrivial behaviour emerges. A propensity criterion for
networking is introduced, consisting in the coexistence within the attractor of
a localized chaotic region, which displays high sensitivity to external
stimuli,and an island of stability, which provides a reliable coupling signal
to the neighbors in the chain. Based on this criterion we compare homoclinic
chaos, recently explored in lasers and conjectured to be typical of a single
neuron, with Lorenz chaos.Comment: 4 pages, 3 figure
Observation and Control of Laser-Enabled Auger Decay
Single photon laser enabled Auger decay (spLEAD) has been redicted
theoretically [Phys. Rev. Lett. 111, 083004 (2013)] and here we report its
first experimental observation in neon. Using coherent, bichromatic
free-electron laser pulses, we have detected the process and coherently
controlled the angular distribution of the emitted electrons by varying the
phase difference between the two laser fields. Since spLEAD is highly sensitive
to electron correlation, this is a promising method for probing both
correlation and ultrafast hole migration in more complex systems.Comment: 5 pages, 3 figure
Two-colour generation in a chirped seeded Free-Electron Laser
We present the experimental demonstration of a method for generating two
spectrally and temporally separated pulses by an externally seeded, single-pass
free-electron laser operating in the extreme-ultraviolet spectral range. Our
results, collected on the FERMI@Elettra facility and confirmed by numerical
simulations, demonstrate the possibility of controlling both the spectral and
temporal features of the generated pulses. A free-electron laser operated in
this mode becomes a suitable light source for jitter-free, two-colour
pump-probe experiments
Time scale synchronization of chaotic oscillators
This paper presents the result of the investigation of chaotic oscillator
synchronization. A new approach for detecting of synchronized behaviour of
chaotic oscillators has been proposed. This approach is based on the analysis
of different time scales in the time series generated by the coupled chaotic
oscillators. This approach has been applied for the coupled Rossler and Lorenz
systems.Comment: 19 pages, 12 figure
Synchronization of chaotic oscillator time scales
This paper deals with the chaotic oscillator synchronization. A new approach
to detect the synchronized behaviour of chaotic oscillators has been proposed.
This approach is based on the analysis of different time scales in the time
series generated by the coupled chaotic oscillators. It has been shown that
complete synchronization, phase synchronization, lag synchronization and
generalized synchronization are the particular cases of the synchronized
behavior called as "time--scale synchronization". The quantitative measure of
chaotic oscillator synchronous behavior has been proposed. This approach has
been applied for the coupled Rossler systems.Comment: 29 pages, 11 figures, published in JETP. 100, 4 (2005) 784-79
Experimental evidence of intrabeam scattering in a free-electron laser driver
Abstract
The effect of multiple small-angle Coulomb scattering, or intrabeam scattering (IBS) is routinely observed in electron storage rings over the typical damping time scale of milliseconds. So far, IBS has not been observed in single pass electron accelerators because charge density orders of magnitude higher than in storage rings would be needed. We show that such density is now available at high brightness electron linacs for free-electron lasers (FELs). We report measurements of the beam energy spread in the FERMI linac in the presence of the microbunching instability, which are consistent with a revisited IBS model for single pass systems. We also show that neglecting the hereby demonstrated effect of IBS in the parameter range typical of seeded VUV and soft x-ray FELs, results in too conservative a facility design, or failure to realise the accessible potential performance. As an example, an optimization of the FERMI parameters driven by an experimentally benchmarked model, opens the door to the extension of stable single spectral line emission to the water window (2.3–4.4 nm), with far-reaching implications for experiments in a variety of disciplines, ranging from physics and chemistry to biology and material sciences, and including nonlinear x-ray optics based on the four-wave-mixing approach.</jats:p
Autonomous Bursting in a Homoclinic System
A continuous train of irregularly spaced spikes, peculiar of homoclinic
chaos, transforms into clusters of regularly spaced spikes, with quiescent
periods in between (bursting regime), by feeding back a low frequency portion
of the dynamical output. Such autonomous bursting results to be extremely
robust against noise; we provide experimental evidence of it in a CO2 laser
with feedback. The phenomen here presented display qualitative analogies with
bursting phenomena in neurons.Comment: Submitted to Phys. Rev. Lett., 14 pages, 5 figure
Imperfect Homoclinic Bifurcations
Experimental observations of an almost symmetric electronic circuit show
complicated sequences of bifurcations. These results are discussed in the light
of a theory of imperfect global bifurcations. It is shown that much of the
dynamics observed in the circuit can be understood by reference to imperfect
homoclinic bifurcations without constructing an explicit mathematical model of
the system.Comment: 8 pages, 11 figures, submitted to PR
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