Jean-Philippe Goddet

Demonstration of relativistic electron beam focusing by a laser-plasma lens

Laser-plasma technology promises a drastic reduction of the size of high-energy electron accelerators. It could make free-electron lasers available to a broad scientific community and push further the limits of electron accelerators for high-energy physics. Furthermore, the unique femtosecond nature of the source makes it a promising tool for the study of ultrafast phenomena. However, applications are hindered by the lack of suitable lens to transport this kind of high-current electron beams mainly due to their divergence. Here we show that this issue can be solved by using a laser-plasma lens in which the field gradients are five order of magnitude larger than in conventional optics. We demonstrate a reduction of the divergence by nearly a factor of three, which should allow for an efficient coupling of the beam with a conventional beam transport line.

Aberration-free laser beam in the soft x-ray range.

By seeding an optical-field-ionized population-inverted plasma amplifier with the 25th harmonic of an IR laser, we have achieved what we believe to be the first aberration-free laser beam in the soft x-ray spectral range. This laser emits within a cone of 1.34 mrad(1/e(2)) at a repetition rate of 10 Hz at a central wavelength of 32.8 nm. The beam exhibits a circular profile and wavefront distortions as low as lambda/17. A theoretical analysis of these results shows that this high beam quality is due to spatial filtering of the seed beam by the plasma amplifier aperture.

Aberration-free high-harmonic source generated with a two-colour field

Imaging experiments of ultrafast phenomena of matter at nanometre-scale require intense, short pulse duration and diffraction-limited soft–X-ray beams, nowadays almost only provided by free-electron lasers. Here, we focused on a table-top soft–X-ray source, which fulfils these fundamental criteria and in addition presents high temporal coherence, the high harmonics generated with a two-colour field (ω+2ω). These harmonics revealed to be free from aberration just by slightly spatially filtering the laser used for generation (ω). Indeed, the measured wavefront distortions, equal to λ/17 RMS at 44 nm, correspond to a diffraction-limited beam. This behaviour is explained by an additional spatial nonlinear filtering effect of the driving laser wavefront, induced here in our particular but simple geometrical configuration of generation by the 2ω component.

High-order harmonic wave fronts generated with controlled astigmatic infrared laser

We report an experimental study on the control of the high-order harmonic wave front through the adjustment of the wave front of the fundamental infrared laser. We have applied different levels of astigmatism to the IR beam via the use of a deformable mirror placed before the lens, and demonstrated that there exists a correlation between the IR and the high harmonic wave fronts.

Electron Transport on COXINEL Beam Line

COXINEL experiment aims at demonstrating free electron laser (FEL) amplification with a laser plasma accelerator (LPA). For COXINEL, a dedicated 8 m transport line has been designed and prepared at SOLEIL. We present here LPA beam transport results around 180 MeV through this line. Different electron beam optics were applied.

A compact ultra-intense plasma-based EUV laser with circular polarization capability

We demonstrated an original technique which allowed us to achieve ultrashort pulse duration EUV lasing by increasing the plasma density. As demonstrated using a lower density amplifier, the emission can be made fully circularly polarized.

Advances in laser driven soft x-ray lasers at LOA

We report spatial and spectral characterization an optical-field-ionized high-order harmonic-seeded soft-x-ray laser. We show that it can be controlled between a regular Gaussian shape and a Bessel profile exhibiting several rings via the IR laser pump intensity. The temporal coherence and spectral linewidth of both the seeded and unseeded soft-x-ray lasers were experimentally measured using a varying path difference interferometer. It showed that the high-order harmonic is subject to a strong spectral narrowing during its propagation in the plasma amplifier without rebroadening at saturation. Also, we present a new method to generate ultra-short x-ray laser pulses by using the laser-driven betatron source to photo-pump inner-shell transitions.

Temporal coherence and spectral width of seeded and ASE XUV lasers

We review recent experimental work devoted to the characterization of the spectral profile and linewidth of two types of XUV lasers seeded by high-order harmonic radiation. The spectral properties were deduced from the measurement of the temporal coherence of the XUV laser pulse, using a variable pathlength interferometer. In this paper an optical-field ionization XUV laser developed at LOA laboratory (France), emitting at 32 nm, and a grazing incidence, and a transient XUV laser developed at Colorado State University (US), emitting at 18.9-nm, both operated in the injection-seeded mode, were investigated. We show that in both cases the measured temporal coherence length is slightly larger than when the lasers are operated in the amplified spontaneous emission (ASE) mode. The corresponding bandwidth is observed to be larger for the transient pumping system, which should more easily scale to sub-picosecond pulse durations.

Caractérisation spatio-temporelle d'un laser XUV injecté

Caracterisation spatio-temporelle d’un laser XUV injecte J.-P. Goddet1, S. Sebban1, O. Guilbaud2, G. Maynard3, B. Cros3, J. Gautier1, Ph. Zeitoun1, C. Valentin1, F. Tissandier1, T. Marchenko1, G. Lambert1, D. Benredjem2, A. Boudaa3, A. Klisnick2, D. Ros2, S. Kazamias2, K. Cassou2,3, J. Habib2, G. Jamelot2, J.-C. Lagron2, D. Joyeux4, S. De Rossi4, D. Phalippou4, F. Delmotte4, M.F. Ravet4, A. Calisti5, T. Mocek6, M. Kozlova6 et K. Jakubczak6

Temporal Coherence and Spectral Linewidth of a Seeded Soft X-Ray Laser Pulse

We present in this paper the first measurement of the spectral profile of a seeded soft x-ray laser. Using a varying path diference interferometer the temporal coherence of a seeded OFI x-ray laser has been experimentally determined, leading to a coherence length of 5ps of the order of the gain lifetime. The measured bandwidth is of order 3.4 mA which is in good agreement with the prediction of a theoretical model presented here.