S. Sebban

Demonstration of a spatial filtering amplifier for high-order harmonics.

We report what is to our knowledge the first demonstration of spatial filtering of a high-order harmonic beam into a soft-x-ray laser plasma amplifier at 32.8 nm. After amplification the seed energy is enhanced by a factor of 50, and the beam profile of the amplified beam exhibits an Airy-like shape due to the spatial filtering by the optical field ionized plasma. Moreover, the transverse coherence of the spatially filtered amplified beam is strongly enhanced, resulting in the generation of a peak coherent power of 0.9 x 10(5) to 1.8 x 10(5) W.

Three-dimensional Maxwell-Bloch calculation of the temporal profile of a seeded soft x-ray laser pulse

We present three-dimensional modeling of amplification of a high-order harmonic seed by a soft x-ray laser plasma. The time-dependent evolution of the x-ray signal is determined from a fully dynamic Maxwell-Bloch calculation. At high seed intensities, a simplified one-dimensional calculation leads to strong Rabi-like temporal oscillations of the output signal. However, such oscillations have not been observed experimentally. Our calculations demonstrate that this is due to spatial non-uniformities in the plasma gain that cause the Rabi oscillations to dampen dramatically. Large amplitude Rabi-like oscillations are expected to appear only in long and uniform plasma. Such targets require optimized guiding techniques.

Synchrotron-like radiation produced from an intense femtosecond laser system

We have produced Larmor x-ray radiation in the keV spectral range from the interaction of an intense and femtosecond laser with an helium gaz jet.

Usefulness of X-ray lasers for science and technology

Recent realization of saturated X-ray lasers (XRLs) has considerably extended the range of optical properties of soft X-ray sources toward high brightness and large coherence length. Consequently, new results may be expected from studies previously experienced with traditional sources such as synchrotron radiation. On the other hand, XRLs open new fields of research owing to their high brightness. In this paper, we present some of the first experiments utilizing XRL sources.

Modelling of an Inner-Shell Photo-Ionization X-Ray Laser Using a Recently Demonstrated Betatron Source

Recent advances in the production of ultra-short intense and collimated x-ray pulses by using fs laser-produced plasmas now allow investigating the old – but not yet demonstrated - inner-shell photo-ionization (ISPI) x-ray laser scheme. This paper will present simulations for lasing near 1.5 nm from NeI pumped by the so-called betatron source which has been developed at LOA and currently delivers in the keV range up to 109 photons per pulse in less than 50 fs.

Collisional optical-field ionization soft x-ray lasers

We report recent investigations on collisional Optical-Field Ionization soft x-ray lasers. The amplifying medium is generated by focusing a high energy circularly polarized, 35 fs 10 Hz Ti: sapphire laser system in a few mm cell filled with gas (xenon or krypton). Using xenon, a gain of 67 cm-1 on the 4d95p-4d95d transition at 41.8 nm in Pd-like xenon and a gain-length product of 15 have been inferred at saturation. This source delivers about 5 109 photons per pulse. Using krypton, a large amplification of the 3d94d-3d94p line at 32.8 nm has been observed for the first time. The influence of the pumping energy and the laser polarization on the lasing output are also presented.

Laser-Driven Plasma-Based Incoherent X-Ray Sources at PALS and ELI Beamlines

In this paper, we report on development of incoherent secondary X-ray sources at the PALS Research Center and discuss the plan for the ELI Beamlines project. One of the approaches, how to generate ultrashort pulses of incoherent X-ray radiation, is based on the interaction of femtosecond laser pulses with underdense plasma. This method, known as laser wakefield electron acceleration (LWFA ), can produce up to GeV electron beams emitting radiation in the collimated beam with a femtosecond pulse duration. This approach was theoretically and experimentally examined at the PALS Center. The parameters of the PALS Ti:Sapphire laser interaction were studied by extensive particle-in-cell (PIC) simulations with radiation postprocessors in order to evaluate the capabilities of our system in this field. The compressed air, and a mixture of helium and argon were used as accelerating medium. The accelerator was operated in the bubble regime with forced self-injection and resulted in the generation of stable relativistic electron beams with the energy up to 80 meV, hence, the betatron X-ray radiation with critical energy in the keV range was generated. The extensions of this method to the ELI Beamlines facility will enable to generate much higher X-ray energies from 10 keV up to 1 meV with 10 Hz repetition rate. Such source is suitable for various applications like phase contrast imaging or X-ray absorption experiments in a single shot.

Overview of Development of Laser Driven Secondary Sources at PALS and ELI

In this paper we report on development of the secondary X-ray sources at the PALS Centre and discuss the plan for the ELI Beamlines project. The spatial and temporal coherence of the most energetic quasi-steady state Ne-like Zn X-ray laser, which is operated at PALS Centre as standard user beamline, was examined proving that amplification of coherent EUV pulses with duration below 1 ps will be possible. Meanwhile, the first transient lasing at PALS Center was achieved using 10 Hz Ti:Sapphire laser chain with peak power of 20 TW as a driver. Finally, we discuss the recent design of laser driven secondary sources generating short coherent or incoherent EUV/X-ray pulses within the ELI Beamlines project.

Architecture and Bloch-Maxwell modelling of multi-mJ 100 fs fully-coherent soft X-ray laser based on X-ray CPA

By seeding amplifying plasmas pumped with the so-called Transient collisionnal excitation scheme, the amplified pulse seems to be limited to an energy of several 10s of μJ. Aiming to attain several mJ, we study the seeding of plasma pumped by long laser pulse. Thanks to our time-dependent Maxwell-Bloch code, we demonstrate that direct seeding with femtosecond pulse is inefficient. We also study the amplification of pulse train with the drawback of re-synchronizing the pulses. We proposed and studied the amplification of high harmonic seed stretched by a grating pair, amplified finally compressed. We consider off-axis diffraction on the gratings for maximizing their efficiency. Considering the phase deformation induced by the amplification and the spectral narrowing the final pulse is 230 fs in duration and 5 mJ.

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