The optimization and advanced study of a laser-plasma electron injector are presented based on a truncated ionization injection scheme for high quality beam production. The smilei code is used with laser envelope approximation and a low number of particles per cell to reach computation time performances enabling the production of a large number of accelerator configurations. The developed and tested workflow is a possible approach for the production of a large dataset for laser-plasma accelerator optimization. A selection of functions of merit used to grade generated electron beams is discussed. Among the significant number of configurations, two specific working points are presented in detail. All data generated are left open to the scientific community for further study and optimization.

A method for the optimisation and advanced studies of a laser-plasma electron injector is presented, based on a truncated ionisation injection scheme for high quality beam production. The SMILEI code is used with laser envelope approximation and a low number of particles per cell to reach computation time performances enabling the production of a large number of accelerator configurations. The developed and tested workflow is a possible approach for the production of large dataset for laser-plasma accelerator optimisation. A selection of functions of merit used to grade generated electron beams is discussed. Among the significant number of configurations, two specific working points are presented in details. All data generated are left open to the scientific community for further study and optimisation.

Exploring new target schemes for laser wakefield accelerators is essential to meet the challenge of increasing repetition rates while ensuring stability and quality of the produced electron beams. The prototyping of a two-chamber gas cell integrated into the beam line and operating in continuous gas flow is introduced and discussed in the frame of ionisation injection. We report the numerical fluid modeling used to assist the density profile shaping. We describe the test bench used for cell prototype assessment, in particular the plasma electron density and longitudinal distribution of species relevant for ionisation injection. The lifetime of the target key part is measured for different materials. Perspectives to high power operation are outlined.

We report on the development and implementation of a diagnostic for the temporal characterization of seeded XUV laser pulses, based on laser-dressed photoionization in the sideband regime, using a home-made velocity map-imaging spectrometer as the central element. The diagnostic was recently tested at the LASERIX facility with the seeded Ne-like titanium laser at 38 eV as the XUV source, overlapped with an infrared pulse of variable duration and intensity.

We present an experimental intensity and wavefront characterization of the infrared vortex driver as well as the extreme ultraviolet vortex obtained through high harmonic generation in an extended generation medium. In a loose focusing geometry, an intense vortex beam obtained through phase-matched absorption-limited high harmonic generation in a 15 mm long Argon filled gas-cell permits single-shot characterization of the vortex structure. Moreover, our study validates the multiplicative law of momentum conservation even for such an extended generation medium.

Optical beams carrying orbital angular momentum are a very active field of research for their prospective applications, especially at short wavelengths. We consider here such beams produced through high-harmonic generation (HHG) in a rare gas and analyze the characterization of their high-charge vortex structure by an extreme ultraviolet Hartmann wavefront sensor. We show that such HHG beams are generally composed of a set of numerous vortex modes. The sensitivity of the intensity and phase of the HHG beam to the infrared laser aberrations is investigated using a deformable mirror.

We presentGuilbaud, Olivier in this paper ongoingSanson, Fabrice studies on seededPandey, Alok plasma-based softPapagiannouli, Eirini X-ray lasers using the LASERIX facilityDemailly, Julien. After an overview of theNeveu, Olivier source setup and characteristicsLucas, Bruno, we will discuss two prospects thatBaynard, Elsa might increase the interest of thesePittman, Moana coherent soft X-ray sources. We haveRos, David successfully generated harmonic beamsHarms, Fabrice carrying Orbital Angular momentum. We brieflyDovillaire, Guillaume present this experiment andRichardson, Martin discuss the remaining challengesBalcou, Philippe for amplifying these kinds of beamsKazamias, Sophie in a plasma-based soft X-ray laser. In the second part, we present numerical results on harmonic seed amplification in conditions leading to Rabi oscillations. This regime is known to be a promising way to reach femtosecond pulses in the present plasma amplifiers. We will discuss the possibility of increasing the stability of such a regime by the introduction of a continuous refractive loss in the gain region.

We demonstrate that high harmonic generation when driven by vortex driver contaminated with various orbital angular momentum (OAM) modes, the upconverted EUV harmonic deviates from perturbative conversion law to exhibit a spectrum of OAM orders.

In this paperSanson, F., we presentPandey, A. K. the characterizationHarms, F. of high charge vortexDovillaire, G. structure of an OAM beam producedBaynard, E. through high-harmonic generationDemailly, J. in a rare gas using an XUV Hartmann wavefrontGuilbaud, O. sensor. We show that the phase-matchedLucas, B. absorption limitedNeveu, O. high-harmonicPapagionnouli, E. generation is ablePittman, M. to retain the high-chargeRos, D. vortex structureRichardson, M. of the XUV beam even inJohnson, E. a rather longLi, W. (1 cm) generationBalcou, Ph. medium. AdditionallyKazamias, S., our recent results on the influence of infrared driver wavefront quality on the characteristics of XUV vortex beam are presented.

Thin-film compression (TFC) and the focusability of high-power laser pulses after self-phase modulation in thin films at transport intensities (similar to 1 TW/cm(2)) for petawatt laser systems is demonstrated. High-energy (similar to 296 mJ) laser pulses are compressed from similar to 55 fs to similar to 31 fs. Additionally, the focusability of high-power (similar to 45-55 TW) flat-top laser pulses after spectral broadening in thin films is found to be largely maintained, showing only modest decreases in the energy contained in the central part of the focal spot. In light of these findings, TFC offers a method for moving toward single-cycle pulse durations at significantly higher energies than those found at present, and if beam instabilities can be mitigated, maybe even higher intensities. (C) 2018 Optical Society of America

We present a start to end (s2e) simulation of the Laser-plasma Wakefield Accelerator (LPWA) foreseen as the ESCULAP project. We use a photo injector to produce a 5MeV 10pC electron bunch with a duration of ∼ 1 ps RMS, it is boosted to 10MeV by a S-band cavity and then compressed to 74 fs RMS (30 fs FWHM) by a magnetic compression chicane (dogleg). After the dogleg, a quadrupole doublet and a triplet are utilized to match the Twiss parameters before injecting into the subsequent plasma wakefield. A 40 TW laser is used to excite plasma wakefield in the 10 cm plasma cell. An optimized configuration has been determined yielding at the plasma exit an electron beam at 180 MeV with energy spread of ∼ 4.2%, an angular divergence of 0.6 mrad and a duration of 4 fs.

We present numerical simulations results on the injection and acceleration of a 10 MeV, 10 pC electrons beam in a plasma wave generated in a gas cell by a 2J, 45 fs laser beam. This modeling is related to the ESCULAP project in which the electrons accelerated by the PHIL photo-injector is injected in a gas cell irradiated by the laser beam of the LASERIX system. Extensive modeling of the experiment was performed in order to determine optimal parameters of the laser plasma configurations. This was done with the newly developed numerical code WakeTraj . We propose a configuration that benefits of a highly compressed electron bunch and for which the injected electron beam can be efficiently coupled to the plasma wave and accelerated up to 140 MeV, with an energy spread lower than 5%.

We demonstrate for the first time, to the best of our knowledge, the ability of extreme ultraviolet (XUV) Hartmann wavefront sensors to characterize high charge vortex beams produced by high-order harmonic generation up to the order of 25. We also show that phase matched absorption limited high harmonic generation is able to maintain the high charge vortex structure of the XUV beam even in a rather long (1 cm) generation medium.

We present theoretical and numerical studies of longitudinal compression and transverse matching of electron bunch before injecting into the Laser-plasma Wake Field Accelerator (LWFA) foreseen at the ESCULAP project in ORSAY. Longitudinal compression is performed with a dogleg chicane, the chicane is designed based on theory of beam optics, beam dynamics in dogleg is studied with ImpactT (Martin Dohlus and Torsten Limberg, 2004) and cross checked with CSRtrack (Qiang and Steve Lidia, 2006), both 3D space charge (SC) and coherent synchrotron radiation (CSR) effects are included. Simulation results show that the energy chirp at the dogleg entrance should be smaller than the nominal optic design value, in order to compensate the negative energy chirp increase caused by longitudinal SC, while CSR can be ignored in our case. With an optimized configuration, the electron bunch (similar to 10 MeV, 10 pC) is compressed from 0.9 ps RMS to 70 fs RMS (53 fs FWHM), with a peak current of 152 A. Transverse matching is realized with a doublet and a triplet, they are matched with Madx and the electron bunch is tracked with ImpactT, simulation results show little difference with the nominal design values, that is due to the SC effect. Finally, by simply adjusting the quadrupole strength, a preliminary optimized configuration has been achieved, that matches the Courant-Snyder (C-S) parameters alpha(x) = 0.01, alpha(y) = -0.02, beta(x) = 0.014 m, beta(y) = 0.012 m at the plasma entrance. (C) 2017 Elsevier B.V. All rights reserved.

Harmonic seeded operation of a neon-like titanium plasma-based soft x-ray laser is described. The plasma amplifier is pumped with a variation of the grazing incidence technique involving a fast and localized ionization step. We discuss its effect on gain dynamics by measuring the amplifying factor as a function of the delay between pump pulse and harmonic seed. Two different regimes are pointed out, following the pumping scheme used. For one of them, a delay in the gain generation compared with the pumping laser pulse is observed.

Seeded operation of a Neon-like Titanium plasma-based soft x-ray laser is described. The plasma amplifier is pumped using a variation of the classical grazing incidence pumping technique, combining a long low energy pulse followed by a main short pulse. Because the preformed plasma is underionized, a part of the main short pulse energy is used to ionized it to the lasing stage. Consequences of this feature on seeded laser properties are discussed.

We demonstrate the use of extreme ultra-violet (EUV) laboratory lasers in probing energy transport in laser irradiated solid targets. EUV transmission through targets containing a thin layer of iron (50 nm) encased in plastic (CH) after irradiation by a short pulse (35 fs) laser focussed to irradiances 3 × 1016 Wcm−2 is measured. Heating of the iron layer gives rise to a rapid decrease in EUV opacity and an increase in the transmission of the 13.9 nm laser radiation as the iron ionizes to Fe5+ and above where the ion ionisation energy is greater than the EUV probe photon energy (89 eV). A one dimensional hydrodynamic fluid code HYADES has been used to simulate the temporal variation in EUV transmission (wavelength 13.9 nm) using IMP opacity values for the iron layer and the simulated transmissions are compared to measured transmission values. When a deliberate pre-pulse is used to preform an expanding plastic plasma, it is found that radiation is important in the heating of the iron layer while for pre-pulse free irradiation, radiation transport is not significant.

We report the first time-resolved study of the photochemistry of chlorine azide (ClN3) by femtosecond velocity-map imaging (fs-VMI). The dissociation dynamics are initiated at 4.6 eV and the photofragments are detected by multiphoton ionization using an intense laser field centered at 803 nm. A dissociation time of 262 ± 38 fs was measured from the rising time of the co-fragments N3 and Cl. The time dependency of the angular distribution of N3, which converges from β2 ~ 2 to β2 = 1.61 ± 0.07 in 170 ± 45 fs, reveals the parallel nature of the transition dipole moment.

In this paper, we have developed a frequency resolved optical gating based on a transient grating generated in Sapphire blade. The input beam is divided in three parts that are focused by a parabolic off-axis mirror (f= 50 mm) within the sapphire.

In most high power laser chains running at 1 µm since the 90’s, the amplification media is Ti:sapphire because of its wide emission spectrum. With a single Ti:sapphire regenerative amplifier the mJ can be easily reached at 800 nm but at 1053 nm the gain is very low and an additional stage of amplification is needed to reach tens of mJ [1].