Three main paths are being developed within the ELI research program for transforming driving laser pulses into bursts of bright short wavelength radiation: high-order harmonic generation in gases, plasma X-ray sources and sources based on relativistic electron beams accelerated in laser plasma. For each of these research areas, dedicated beamlines are built to provide a unique combination of X-ray sources to the scientific community. The application of these beamlines has a well-defined balance between fundamental science and applications in different fields of science and technology. Here we summarize the current status of those user beamlines and we introduce new diagnostics devices developed within the implementation phase of the project, namely compact XUV spectrometer and beam profiler that is using only one fixed detector and an imaging Michelson interferometer with increased sensitivity for low density gas jet characterization.
We will be giving an overview on the development of the “ELI-beamline facility” being currently implemented and opened as a user facility within the Extreme Light Infrastructure (ELI) project based on the European ESFRI (European Strategy Forum on Research Infrastructures) process.
ELI-Beamlines is the high-energy, repetition-rate laser pillar of the ELI (Extreme Light Infrastructure) project. The main objective of the ELI-Beamlines facility is the delivery of ultra-intense high-energy pulses for high field experiments and the generation and applications of high-brightness X-ray sources and accelerated particles. The high power laser systems currently prepared and used for the generation of higher repetition rate sources of x-rays and particles are L1 (Allegra) a 1 kHz diode pumped laser produced sub-20fs OPCPA system and the L3 (HAPLS) a 10 Hz, 1 PW (30fs) laser using as the active medium Ti:sapphire with new gas cooled diode pumped Nd doped Glass pump laser. The lasers will be able to provide focused intensities attaining >1018-21 Wcm-2 suitable for generation of x-rays and particles (electrons and ions). We will discuss the infrastructure concerning the availability of experimental areas, including secondary sources of particles and x-rays in the wavelength range between 20 eV-100 keV and few Mev and their practical implementation at the ELI-Beamline user facility. The sources are either based on direct interaction of the laser beams with gaseous targets (high order harmonics) or will first accelerate electrons which then will interact with laser produced wigglers (Betatron radiation) or directly injected into undulators (laser driven LUX or later X-FEL). The direct interaction (collision) of laser accelerated electrons with the intense focused laser again will lead to short pulse high energy radiation via Compton or Thomson scattering for different applications opening also the route to fundamental physics investigations in high intensity interaction due to the 4 gamma 2 Lorentz boost of the intensity seen by high energy (GeV- > 106) electrons.
We present lasing in Ni-like molybdenum x-ray laser (18.9 nm) demonstrated with grazing incidence pumping and complete diagnostics of the generated EUV beam. This source of EUV radiation was the first experimental realization of transient x-ray laser at the PALS laboratory. The experiment was performed on a 10 Hz Ti:Sapphire laser system with highly efficient grazing incidence pumping by single beam with profiled laser pulse which included a long prepulse followed by a short main pump pulse. The plasma column was created by focusing of the pumping laser beam on a slab target by a spherical mirror in two different off-axis configurations. Lasing close to saturation with EUV pulses of energy around 100 nJ was demonstrated with less than 500 mJ pumping energy on target. Experimental data from far-field images were analyzed by applying the generalized Van Cittert-Zernike theorem which in general relates field correlation function at the source with intensity in the far-field and can give information about the source size.
Relativistic electron beams accelerated by laser wakefield have the ability to serve as sources of collimated,
point-like and femtosecond X-ray radiation. Experimental conditions for generation of stable quasi-monoenergetic
electron bunches using a femtosecond few-terawatt laser pulse (600 mJ, 50 fs) were investigated as they are crucial
for generation of stable betatron radiation and X-ray pulses from inverse Compton scattering. A mixture of helium
with argon, and helium with an admixture of synthetic air were tested for this purpose using different backing
pressures and the obtained results are compared. The approach to use synthetic air was previously proven to stabilize
the energy and energy spread of the generated electron beams at the given laser power. The accelerator was operated
in nonlinear regime with forced self-injection and resulted in the generation of stable relativistic electron beams with
an energy of tens of MeV and betatron X-ray radiation was generated in the keV range. A razor blade was tested to
create a steep density gradient in order to improve the stability of electron injection and to increase the total electron
bunch charge. It was proven that the stable electron and X-ray source can be built at small-scale facilities, which
readily opens possibilities for various applications due to availability of such few-terawatt laser systems in many
laboratories around the world.
In a plasma wakefield accelerator, an intense laser pulse propagates in an under-dense plasma that drives a relativistic plasma wave in which electrons can be injected and accelerated to relativistic energies within a short distance. These accelerated electrons undergo betatron oscillation and emit a collimated X-ray beam along the direction of electron velocity. This X-ray source is characterised with a source size of the order of a micrometer, a pulse duration of the order of femtosecond, and with a high spectral brightness. This novel X-ray source provides an excellent imaging tool to achieve unprecedented high-resolution image through phase contrast imaging. The phase contrast technique has the potential to reveal structures which are invisible with the conventional absorption imaging. In the X-ray phase contrast imaging, the image contrast is obtained thanks to phase shifts induced on the X-rays passing through the sample. It involves the real part of refractive index of the object. Here we present high-resolution phase contrast X-ray images of two biological samples using laser-driven Betatron X-ray source.
A PW Ti:Sapphire laser with 30-J energy and 30-fs pulse duration has been developed at GIST and applied to generate
x-rays and energetic charged particles. We present the status and plan of developing ultrashort x-ray sources and their
applications. We successfully demonstrated x-ray lasers and their applications to high-resolution imaging. In addition,
we plan to generate high flux x-ray/gamma-ray sources using the PW laser.
Using a zone plate interferometer we have demonstrated image-plane holographic microscopy employing the radiation of
a compact capillary discharge Ar laser operating at 46.9 nm for illumination. In this paper we describe a full analysis of
the spatial resolution of the system and demands on the coherence of the radiation. The analysis shows that the resolution
in the amplitude and phase images is mainly determined by the numerical aperture of the imaging element and the
wavelength of the illumination. The resolution, however, is not affected by the degree of coherence, which only reduces
the field of view. We also show rather low demands on temporal coherence due to the common-path interferometric
The results of development and applications of the secondary sources at PALS Center will be presented. Currently the
iodine system and the Ti:Sapphire system are operating at the PALS Center as driving lasers for generation of secondary
sources. The iodine system with net energy of 1kJ is used for QSS X-ray lasing schemes. The most robust and most
energetic QSS scheme with this driver is the Ne-like Zn X-ray laser, which is working here as standard user beamline for
diverse applications. Recent experiment devoted to temporal coherence measurement shows possibility to amplify short
duration X-rays. The second system with high rep rate is Ti: Sapphire laser chain with peak power 20TW. This laser
system is used for generation high order harmonics and transient collisionally excited X-ray lasers.
Extensive measurements of wavefront profile of the coherent XUV (eXtreme Ultra-Violet) HHG (High-order Harmonics Generation) beam at the wavelength of 30 nm have been performed. Unique results have been achieved using the PDI (Point Diffraction Interferometer) technique. The basic principle of the PDI is straightforward – ultrathin aluminium foil with a miniature pinhole – and it benefits from the self-referencing feature which is very important due to the measured wavelength. On the other hand, fabrication and experimental measurements are in general difficult in this spectral domain. In this paper we present basic principles, experimental setup, alignment techniques, obtained data and their analysis.
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.
We present an overview of the Ti:sapphire laser chain recently commissioned at the PALS laboratory. The laser is based on
commercial laser units and of an in-house-designed-and-built compressor. The system provides peak power of 25 TW in <40-fs
pulses and delivers up to 0.9 J on the target in the main beam, at a repetition rate of 10 Hz. The laser chain employs conventional
CPA amplification technique consisting of oscillator, stretcher, regenerative amplifier, pulse picker, and multipass amplifier,
followed by compressor. The compressor is designed to use residual zero diffraction orders to produce two additional 50-mJ beams.
One of these beams is compressed by an additional small-size compressor. All three beams can be delayed with respect to each other
in the range of about 0-20 ns. The beams are delivered by vacuum distribution system into a target room serving to development of
sources of X-rays and accelerated particles. In the near future the system will be synchronized with the PALS kJ laser and will serve
as an ultrafast diagnostic probe beam.
We present the results of an experiment concerning laser-plasma interaction in the regime relevant to shock ignition. The
interaction of high-intensity frequency tripled laser pulse with CH plasma preformed by lower intensity pre-pulse on
fundamental wavelength of the kJ-class iodine laser was investigated in the planar geometry in order to estimate the
coupling of the laser energy to the shock wave or parametric instabilities such as stimulated Raman or Brillouin
scattering, or to the fast electrons. First the complete characterization of the hydrodynamic parameters of preformed
plasma was made using crystal spectrometer to estimate the electron temperature and XUV probe to resolve the electron
density profile close to the critical density region. The other part of the experiment consisted of the shock chronometry,
calorimetry of the back-scattered light and hard X-ray spectrometry to evaluate the coupling to different processes. The
preliminary analysis of the measurements showed rather low energy transfer of the high-intensity pulse to back-scattered
light (< 5%) and no traces of any significant hot electron production were found in the X-ray spectra.
We review development in the repetition-rate target area systems and technologies within the Work Package 15 of the
HiPER Preparatory Phase project. The activities carried out in 2009-2010 have been involving analysis of solutions and
baseline design of major elements of the repetition-rated fusion chamber, analysis of prospective injector technologies,
numerical modelling of target survival during acceleration phase and during flight in the environment of fusion
chamber, analysis of options of remote handling, systems of mitigation of fusion debris, and others. The suggested
solutions assume operation at the repetition rate of 10 Hz and fusion yield between 20 and 100 MJ. Shock ignition is
assumed as the baseline ignition scenario, although some technologies are applicable in the fast ignition; a number of
the technologies identified are exploitable as well in the indirect drive. The operation of the HiPER repetition-rate
chamber will contribute to technology development for the Demonstration Reactor HiPER facility.
Inertial Confinement Fusion with Shock Ignition relies on a very strong shock created by a laser pulse at an intensity of
the order of 1016W/cm2. In this context, an experimental campaign at the Prague Asterix Laser System (PALS) has been
carried out within the frame of the HiPER project. Two beams have been used, the first to create an extended preformed
plasma (scale length of the order of hundreds of micrometers) on a planar target, the second to generate a strong shock
wave. Different diagnostics were used to study both the shock breakout at the rear surface of the target and the laserplasma
coupling and parametric instabilities. This paper is focused on back-scattering analysis to measure the backreflected
energy and to characterize parametric instabilities such as stimulated Brillouin and Raman scattering. Our
experimental data show that parametric instabilities do not play a strong role in the laser plasma coupling. Moreover,
preliminary analysis of the back reflected light from the interaction region shows that less than 5% of the total incident
laser energy was back-reflected, with only a small fraction of that light was originating from parametric instabilities.
ELI-Beamlines will be a high-energy, repetition-rate laser pillar of the ELI (Extreme Light Infrastructure) project. It will
be an international facility for both academic and applied research, slated to provide user capability since the beginning
of 2016. The main objective of the ELI-Beamlines Project is delivery of ultra-short high-energy pulses for the
generation and applications of high-brightness X-ray sources and accelerated particles. The laser system will be
delivering pulses with length ranging between 10 and 150 fs and will provide high-energy petawatt and 10-PW peak
powers. For high-field physics experiments it will be able to provide focused intensities attaining 10<sup>24</sup> Wcm<sup>-2</sup>, while this
value can be upgraded in a later phase without the need to upgrade the building infrastructure. In this paper we describe
the overall conception and layout of the designed ELI-Beamlines facility, and review some essential elements of the
This paper presents the goals and some of the results of experiments conducted within the Working Package 10 (Fusion
Experimental Programme) of the HiPER Project. These experiments concern the study of the physics connected to
"Advanced Ignition Schemes", i.e. the Fast Ignition and the Shock Ignition Approaches to Inertial Fusion. Such schemes
are aimed at achieving a higher gain, as compared to the classical approach which is used in NIF, as required for future
reactors, and making fusion possible with smaller facilities.
In particular, a series of experiments related to Fast Ignition were performed at the RAL (UK) and LULI (France)
Laboratories and were addressed to study the propagation of fast electrons (created by a short-pulse ultra-high-intensity
beam) in compressed matter, created either by cylindrical implosions or by compression of planar targets by (planar)
laser-driven shock waves. A more recent experiment was performed at PALS and investigated the laser-plasma coupling
in the 10<sup>16</sup> W/cm<sup>2</sup> intensity regime of interest for Shock Ignition.
High-harmonic-seeded x-ray laser became an important issue in x-ray laser development due to the possibility to obtain a
highly coherent and polarized soft x-ray source. We performed theoretical investigations into amplification of high
harmonic pulses in an x-ray lasing medium by using a model based on Maxwell-Bloch equations. From the theoretical
works, we analyze characteristics of energy extraction and temporal profile of output pulse. In addition, preliminary
experimental results and ongoing experiments related the harmonic-seeded x-ray lasers are reported.
We present an experimentally simple technique for the measurement of electron density gradients in dense laser plasmas (the plasma region of electron density up to 10<sup>24</sup> cm<sup>-3</sup> can be investigated with the use of available XRLs). The distortion
of the XRL wave-front caused by the gradients of the electron density is measured using Talbot pattern deformation. The plasma probed by the XRL is imaged on the CCD plane, then a 2D grating is put in front of the chip so that the Talbot plane of this grating fits on the CCD. The compromise between the spatial resolution and the sensitivity for the given wavelength of the probe must be set within the grating design. The main advantages of this method are low
requirements on spatial coherence of the probing beam as well as the simple alignment, which are the main difficulties of interferometry using radiation of XRLs.
Results of a novel X-ray laser application, aimed at understanding the microscopic effects involved in formation of laserinduced
damage in optical materials exposed to sub-ns laser pulses, will be presented. Specifically, we studied thin plane
beamsplitters that are presently the weakest element of the next generation of high-energy lasers (LMJ, NIF), with
permanent damage threshold below 20 J/cm<sup>2</sup>. Standard fused silica substrates and a model system, containing welldefined
micron grooves as seeding sites to trigger damage when irradiated by 438 nm laser pulses, were in situ probed by
a neon-like zinc X-ray laser delivering up to 10 mJ at 21.2 nm. The probing beamline employed a double Lloyd's mirror
interferometer, used in conjunction with an imaging mirror to provide magnification of ~8. In conjunction with an array
of in-situ optical diagnostics, one of the questions addressed was whether the damage (transient or permanent) on the
rear surface of the beamsplitter occurs during or after the laser pulse, i.e. whether it is due to local electrical fields or to
other processes. Another issue, examined by both the X-ray interferometric microscopy and the optical diagnostics, is
whether a local rear-surface modification is associated with non-linear effects (self-focusing, filamentation) of the laser
beam in the bulk.
For the purpose of the wavefront profile measurement of XUV beams emitting at 21.2 nm and 30 nm, we designed the
PDI (Point Diffraction Interferometer) wavefront sensor. PDI is a self-referencing monolithic device consisting of a thin
neutral filter and a very small pinhole located near the axis of the XUV beam focal spot. The small pinhole works as a
diffraction aperture generating a reference spherical wave, and working as well as a spatial filter. The material of the thin
foil is partially transparent for the XUV radiation, and it determines the visibility of the interference fringes. The
interference pattern is recorded by an XUV detector placed behind the foil. From the information encoded in the pattern
it is possible sequentially to reconstruct the beam wavefront profile. We will discuss the design and optimization of the
PDI wavefront sensor setup.