Christophe Szwaj

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Relativistic electron bunches circulating in accelerators are subjected to a dynamical instability leading to microstructures at millimeter to centimeter scale. Although this is a well-known fact, direct experimental observations of the structures, or the field that they emit, remained up to now an open problem. Here, we report the direct, shot-by-shot,(More)
Experimental evidence of convective and absolute instabilities in a nonlinear optical system is given. In optics, the presence of spatial nonuniformities brings in additional complexity. Hence, signatures characterizing these two regimes are derived based on analytical and numerical investigations. The corresponding noise-sustained and dynamical patterns(More)
Optical fibres are favourable tabletop laboratories to investigate both coherent and incoherent nonlinear waves. In particular, exact solutions of the one-dimensional nonlinear Schrödinger equation such as fundamental solitons or solitons on finite background can be generated by launching periodic, specifically designed coherent waves in optical fibres. It(More)
We present the first high resolution (10(-3) cm(-1)) interferometric measurements in the 200-750 GHz range using coherent synchrotron radiation, achieved with a low momentum compaction factor. The effect of microbunching on spectra is shown, depending on the bunch current. A high signal-to-noise ratio is reached thanks to an artifact correction system based(More)
Emission of light by a single electron moving on a curved trajectory (synchrotron radiation) is one of the most well-known fundamental radiation phenomena. However experimental situations are more complex as they involve many electrons, each being exposed to the radiation of its neighbors. This interaction has dramatic consequences, one of the most(More)
We evidence numerically and experimentally that advection can induce spectrotemporal defects in a system presenting a localized structure. Those defects in the spectrum are associated with the breakings induced by the drift of the localized solution. The results are based on simulations and experiments performed on the super-ACO free-electron laser.(More)
We investigate a fundamental limitation occurring in vacuum ultraviolet and extreme ultraviolet seeded free electron lasers (FELs). For a given electron beam and undulator configuration, an increase of the FEL output energy at saturation can be obtained via an increase of the seed pulse duration. We put in evidence a complex spatiotemporal deformation of(More)
Single-shot recording of terahertz electric signals has recently become possible at high repetition rates, by using the photonic time-stretch electro-optic sampling (EOS) technique. However the moderate sensitivity of time-stretch EOS is still a strong limit for a range of applications. Here we present a variant enabling to increase the sensitivity of(More)
In recent synchrotron radiation facilities, the use of short (picosecond) electron bunches is a powerful method for producing giant pulses of terahertz coherent synchrotron radiation. Here we report on the first direct observation of these pulse shapes with a few picoseconds resolution, and of their dynamics over a long time. We thus confirm in a very(More)
In spatiotemporal systems with advection, suppression of noise-sustained structures involves questions that are outside of the framework of deterministic dynamical systems control (such as Ott-Grebogi-Yorke-type methods). Here we propose and test an alternate strategy where a nonlocal additive feedback is applied, with the objective to create a new(More)
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