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The photonic time-stretch technique allows electric field pulse shapes to be recorded with picosecond resolution, at megahertz acquisition rates. Using this strategy, we could directly record spatial patterns that spontaneously appear in relativistic electron bunches, and follow their dynamical evolution over time. We present recent results obtained using two strategies. At SOLEIL, we present the shapes of the THz pulses which are emitted by the structures, and detected far from the emission point, at the end of a beamline. At ANKA, we present how it has been possible to monitor directly the electron bunch near-field. These new types of single-shot recordings allow direct and stringent tests to be performed on electron bunch dynamical models in synchrotron radiation facilities.

Photonic time-stretch enables to record electric field pulse shapes with picosecond resolution, at megahertz acquisition rates. Using this strategy, we could record the complex spatiotemporal evolution of relativistic electron bunches circulating in storage ring accelerators. We tested two complementary approaches. At SOLEIL, we monitored the THz pulses of coherent synchrotron that are emitted by the electrons. At ANKA, we monitored directly the electron bunch near-field.

We consider the problem of shot-by-shot acquisition of pulse shapes at high repetition rate in accelerator-basedsystems. More speci cally, we examine the two-step strategy consisting in (i) encoding the pulse information ontoa laser pulse, and (ii) use the so-called time-stretch strategy to \slow-down" the information before recording.We thus show that the repetition rate of already existing electro-optic sampling setups can be straightforwardlyincreased up to the 100 10 6 pulses/s range, and make a demonstration for the detection of coherent THz pulses.The strategy is however not limited to electro-optic sampling of THz pulses or electron bunches. It can be appliedto other types of wavelengths, provided the desired information (as e.g., FEL pulses or electron bunches shapes)can be imprinted onto a laser pulse.Keywords: Coherent Synchrotron Radiation, Electro-optic sampling, Photonic time-stretch, Terahertz optics 1. INTRODUCTION In accelerator-based coherent sources, there is a growing need for pulse shape characterization at high repetitionrates. High repetition rates is encountered in existing Free-Electron Lasers (FEL), when the emission is composedof bursts of pulses at multi-MHz repetition rates.

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 spectacular being the spontaneous formation of spatial structures inside electrons bunches. This fundamental effect is actively studied as it represents one of the most fundamental limitations in electron accelerators, and at the same time a source of intense terahertz radiation (Coherent Synchrotron Radiation, or CSR). Here we demonstrate the possibility to directly observe the electron bunch microstructures with subpicosecond resolution, in a storage ring accelerator. The principle is to monitor the terahertz pulses emitted by the structures, using a strategy from photonics, time-stretch, consisting in slowing-down the phenomena before recording. This opens the way to unpreceeded possibilities for analyzing and mastering new generation high power coherent synchrotron sources., Comment: 7 pages, 6 figures

The LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) in France aims at investigating the generation of short, intense, and coherent pulses in the soft x-ray region (with two particular targeted wavelengths of 20 and 13 nm). It consists in a single Free Electron Laser (FEL) line with cryo-ready in-vacuum undulators using a Conventional Linear Accelerator (CLA) using the superconducting technology of 400 MeV or a Laser Wake Field Accelerator (LWFA) ranging from 0.4 to 1 GeV with multi-TW or PW lasers. The FEL line can be operated in the seeded (High order Harmonic in Gas seeding) and Echo Enable Harmonic Generation configurations, which performances will be compared. Two pilot user experiments for time-resolved studies of isolated species and magnetization dynamics will take benefit of LUNEX5 FEL radiation.

One of the main advantages of Nd-YAG lasers compared to CO2 lasers consists of easy beam handling using optical silica fibers. However, up to now Nd-YAG applications for material processing were limited due to a rather low available mean output power (less than about 500 W). A Eureka project (termed "EU-226") which consequently aimed at developing the so called "High Power Solid State Laser (HPSSL)" capable of 1 to 3 kW, involved absorptivity studies results of which are given in this contribution. Metallic surfaces exhibit a higher absorptivity at 1.06 µm (Nd-YAG) than at 10.6 µm which improves the energy transfer with a Nd-YAG laser and decreases the thermal runaway. This was acertained by measurements of absorptivity as a function of temperature and by thermal cycle calculations. This permits laser surface hardening of steels without any coating or gas shielding, which prevents in particular pollution. Various materials, I. e. pure nickel, Inconel 718 and AISI 1045 steel, were studied, featuring in particular the influence of surface roughness, oxidation and initial absorptivity on laser-material interaction.