Search

We present the design and implementation of a new, modular gas target suitable for high-order harmonic generation using high average power lasers. To ensure thermal stability in this high heat load environment, we implement an appropriate liquid cooling system. The system can be used in multiple-cell configurations, allowing us to control the cell length and aperture size. The cell design was optimized with heat and flow simulations for thermal characteristics, vacuum compatibility, and generation medium properties. Finally, the cell system was experimentally validated by conducting high-order harmonic generation measurements using the 100 kHz high average power HR-1 laser system at the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI ALPS) facility. Such a robust, versatile, and stackable gas cell arrangement can easily be adapted to different experimental geometries in both table-top laboratory systems and user-oriented facilities, such as ELI ALPS.

Laser wakefield acceleration (LWFA) using PW-class laser pulses generally requires cm-scale laser–plasma interaction Rayleigh length, which can be realized by focusing such pulses inside a long underdense plasma with a large f-number focusing optic. Here, we present a new PW-based LWFA instrument at the SG-II 5 PW laser facility, which employs f/23 focusing. The setup also adapted an online probing of the plasma density via Nomarski interferometry using a probe laser beam having 30 fs pulse duration. By focusing 1-PW, 30-fs laser pulses down to a focal spot of 230 µm, the peak laser intensity reached a mild-relativistic level of 2.6 × 1018 W/cm2, a level modest for standard LWFA experiments. Despite the large aspect ratio of >25:1 (transverse to longitudinal dimensions) of the laser pulse, electron beams were observed in our experiment only when the laser pulse experienced relativistic self-focusing at high gas-pressure thresholds, corresponding to plasma densities higher than 3 × 1018 cm−3.

We present the results of microscopic and macroscopic simulations on electron quantum path interferences during high harmonic generation in atomic gas medium driven by various ultrashort chirped driving laser pulses.

We present the experimental realization of spectrally tunable, ultrashort, quasi-monochromatic extreme ultraviolet (XUV) pulses generated at 100 kHz repetition rate in a user-oriented gas high harmonic generation (GHHG) beamline of the Extreme Light Infrastructure - Attosecond Light Pulse Source (ELI ALPS) facility. Versatile spectral and temporal shaping of the XUV pulses are accomplished with a double-grating, time-delay compensated monochromator accommodating the two composing stages in a novel, asymmetrical geometry. This configuration supports the achievement of high monochromatic XUV flux (2.8+/-0.9*1e10 photons/s at 39.7 eV selected with 700 meV FWHM bandwidth) combined with ultrashort pulse duration (4.0+/-0.2 fs using 12.1+/-0.6 fs driving pulses) and small spot size (sub-100 um). Focusability, spectral bandwidth, and overall photon flux of the produced radiation were investigated covering a wide range of instrumental configurations. Moreover, complete temporal (intensity and phase) characterization of the few-femtosecond monochromatic XUV pulses - a goal that is difficult to achieve by conventional reconstruction techniques - has been realized using ptychographic algorithm on experimentally recorded XUV-IR pump-probe traces. The presented results contribute to in-situ, time-resolved experiments accessing direct information on the electronic structure dynamics of novel target materials., Comment: 20 pages, 8 figures

We investigate the electron quantum path interference effects during high harmonic generation in atomic gas medium driven by ultrashort chirped laser pulses. To achieve that, we identify and vary the different experimentally relevant control parameters of such a driving laser pulse influencing the high harmonic spectra. Specifically, the impact of the pulse duration, peak intensity and instantaneous frequency is studied in a self-consistent manner based on Lewenstein formalism. Simulations involving macroscopic propagation effects are also considered. The study aims to reveal the microscopic background behind a variety of interference patterns capturing important information both about the fundamental laser field and the generation process itself. The results provide guidance towards experiments with chirp control as a tool to unravel, explain and utilize the rich and complex interplay between quantum path interferences including the tuning of the periodicity of the intensity dependent oscillation of the harmonic signal, and the curvature of spectrally resolved Maker fringes., 25 pages, 8 figures, final version, New J. Phys. 23123012 (2021)

Attoscience is the emerging field that accesses the fastest electronic processes occurring at the atomic and molecular length scales with attosecond (1 as = 1 0 − 18 s) time resolution having wide ranging physical, chemical, material science and biological applications. The quintessential and one of the most fundamental processes in this domain is the generation of phase locked XUV attosecond pulses. The theoretical approach to understand the process incorporates a fully quantum or semi classical or relativistic description of coherent charge dynamics in intense ultrashort electromagnetic fields driving a quantum system (an atom, a molecule, solid band gap materials or surface plasmas). Modelling of such physical and dynamical systems in science and also in many other branches often leads to equations represented in terms of complex multi-dimensional integrals. These integrals can often be solved using the stationary phase approximation, which leads to a series of equations identifying the points in the multi-dimensional space, having most significant contributions in their evaluation. These points are usually indicated as saddle points. The description of the dynamics of quantum mechanical or relativistic systems that results from such an approach enables near to classical physics intuitive perceptions of the processes under investigation. Thus, the saddle point methods are very powerful and valuable general theoretical tools to obtain asymptotic expressions of such solutions and help also to gain physical insights on the underlying phenomena. Such techniques developed in the past have been adapted to study the emission of as pulses by different physical systems and have been widely employed in calculating and estimating the response of matter to intense electromagnetic pulses on ultrafast time scales. Here we provide an extensive disposition of the saddle point approaches unifying their ubiquitous applications within the domain of attoscience valid for simple atomic to more complex condensed matter systems undergoing ultrafast dynamics and present current trends and advancements in the field. In this review we would delineate the methodology, present a synthesis of seminal works and describe the state of the art applications. Finally we also address ultrashort time dynamics of novel materials that have gained much attention recently, namely lower dimensional material systems and micro-plasma systems.

This work demonstrates that black phosphorene, a two dimensional allotrope of phosphorus, has the potential to be an efficient photo-thermionic emitter. To investigate and understand the novel aspects we use a combined approach in which ab initio quantum simulation tools are utilized along with semiclassical description for the emission process. First by using density functional theory based formalism, we study the band structure of phosphorene. From the locations of electronic bands, and band edges, we estimate the Fermi level and work function. This leads us to define a valid material specific parameter space and establish a formalism for estimating thermionic electron emission current from phosphorene. Finally we demonstrate how the emission current can be enhanced substantially under the effect of photon irradiation. We observe that photoemission flux to strongly dominate over its coexisting counterpart thermionic emission flux. Anisotropy in phosphorene structure plays important role in enhancing the flux. The approach which is valid over a much wider range of parameters is successfully tested against recently performed experiments in a different context. The results open up a new possibility for application of phosphorene based thermionic and photo-thermionic energy converters.

International audience; Quantum-optical spectrometry is a recently developed shot-to-shot photon correlation-based method, namely using a quantum spectrometer (QS), that has been used to reveal the quantum optical nature of intense laser–matter interactions and connect the research domains of quantum optics (QO) and strong laser-field physics (SLFP). The method provides the probability of absorbing photons from a driving laser field towards the generation of a strong laser–field interaction product, such as high-order harmonics. In this case, the harmonic spectrum is reflected in the photon number distribution of the infrared (IR) driving field after its interaction with the high harmonic generation medium. The method was implemented in non-relativistic interactions using high harmonics produced by the interaction of strong laser pulses with atoms and semiconductors. Very recently, it was used for the generation of non-classical light states in intense laser–atom interaction, building the basis for studies of quantum electrodynamics in strong laser-field physics and the development of a new class of non-classical light sources for applications in quantum technology. Here, after a brief introduction of the QS method, we will discuss how the QS can be applied in relativistic laser–plasma interactions and become the driving factor for initiating investigations on relativistic quantum electrodynamics.

We generate high-order harmonics in gaseous medium with tunable photon energy using time domain interferometry of double pulses in a non-collinear generation geometry. The method is based on the fact that the generated harmonics inherit certain spectral properties of the driving laser. The two temporally delayed ultrashort laser pulses, identical in all parameters, are produced by a custom-made split-and-delay unit utilizing wave front splitting without a significant energy loss. The arrangement is easy to implement in any attosecond pulse generation beamline, and is suitable for the production of an extreme ultraviolet source with simply and quickly variable central photon energy, useful for a broad range of applications., 6 pages, 5 figures, after peer-review

Laser induced x-ray fluorescence were observed against laser polarization ellipticity. While emission from krypton peaks at linear polarization, a signature of recollision, emission from neon shows opposite trend. We attribute it to two competing processes.

We propose a technique to control the spectral characteristics of high-harmonic sources. The method is easily implementable in any attosecond-pulse generation beamline, regardless of the driving laser, thereby satisfying different experimental needs.

We report the generation of 50 pJ attosecond pulse trains at 100-kHz using a high average-power annular laser beam, which is the highest one until now among systems of repetition rate higher than 10 kHz.

Intense ultrafast laser interaction with solid-density plasma can lead to relativistic transient electron dynamics that are favorable for the generation of high-field terahertz (THz) pulses. We investigate the temporal characteristics of such THz pulses. Single-shot electro-optic measurements enable us to record the complete temporal profiles of the THz pulses emanating from planar $\mathrm{Cu}$ and aligned $\mathrm{Cu}$-nanorod-array plasma. The temporal properties of the THz pulses exhibit several transients. Fully relativistic two-dimensional particle-in-cell simulations corroborate experimental observations and reveal that these features originate from electron microbunch emission from the target. Our results demonstrate that target nanostructuring provides a route to control such ultrafast electron dynamics and hence THz-pulse properties in the time domain.

This work theoretically investigates high-order harmonic generation in rare gas atoms driven by two temporally delayed ultrashort laser pulses. Apart from their temporal delay, the two pulses are identical. Using a single-atom model of the laser-matter interaction it is shown that the photon energy of the generated harmonics is controllable within the range of one eV -- a bandwidth comparable to the photon energy of the fundamental field -- by varying the time delay between the generating laser pulses. It is also demonstrated that high-order harmonics generated by double pulses have advantageous characteristics, which mimick certain properties of an extreme ultraviolet (XUV) monochromator. With the proposed method, a simpler setup at a much lower cost and comparatively higher spectral yield can be implemented in contrast to other approaches., Comment: 7 pages, 6 figures, after peer-review, corrected typo in author list

Electron quantum path interferences in strongly laser-driven aligned molecules and their dependence on the molecular alignment is an essential open problem in strong-field molecular physics. Here, we demonstrate an approach which provides direct access to the observation of these interference processes. The approach is based on the combination of the time-gated-ion-microscopy technique with a pump-probe arrangement used to align the molecules and generate high-order harmonics. By spatially resolving the interference pattern produced by the spatiotemporal overlap of the harmonics emitted by the short and long electron quantum paths, we have succeeded in measuring in situ their phase difference and disclose their dependence on molecular alignment. The findings constitute a vital step towards an understanding of strong-field molecular physics and the development of attosecond spectroscopy approaches without the use of auxiliary atomic references., Comment: 7 pages, 3 figures

Electrodynamical processes induced in complex systems like semiconductors by strong electromagnetic fields have traditionally been described using semiclassical approaches. Although these approaches allowed the investigation of ultrafast dynamics in solids culminating in multipetahertz electronics, they do not provide any access to the quantum-optical nature of the interaction, as they treat the driving field classically and unaffected by the interaction. Here, using a full quantum-optical approach, we demonstrate that the subcycle electronic response in a strongly driven semiconductor crystal is imprinted in the quantum state of the driving field resulting in nonclassical light states carrying the information of the interaction. This vital step towards strong-field ultrafast quantum electrodynamics unravels information inaccessible by conventional approaches and leads to the development of a new class of nonclassical light sources.

We report the application of the time gated ion microscopy technique in accessing online the position of the source of harmonics generated in atomic gas media. This is achieved by mapping the spatial extreme-ultraviolet (XUV)-intensity distribution of the harmonic source onto a spatial ion distribution, produced in a separate focal volume of the generated XUV beam through single photon ionization of atoms. It is found that the position of the harmonic source depends on the relative position of the harmonic generation gas medium and the focus of the driving infrared (IR) beam. In particular, by translating the gas medium with respect to the IR beam focus different virtual source positions are obtained online. Access to such online source positioning allows better control and provides increased possibilities in experiments where selection of electron trajectory is important. The present study gives also access to quantitative information which is connected to the divergence, the coherence properties and the photon flux of the harmonics. Finally, it constitutes a precise direct method for providing complementary experimental info to different attosecond metrology techniques., Comment: 7 pages, 3 figures

Relativistic surface high harmonics have been considered a unique source for the generation of intense isolated attosecond pulses in the extreme ultra-violet and x-ray spectral ranges. Their practical realization, however, is still a challenging task and requires identification of optimum experimental conditions and parameters. Here, we present measurements and particle-in-cell simulations to determine the optimum values for the most important parameters. In particular, we investigate the dependence of harmonics efficiency, divergence, and beam quality on the pre-plasma scale length as well as identify the optimum conditions for generation of isolated attosecond pulses by measuring the dependence of the harmonics spectrum on the carrier - envelope phase of the driving infrared field. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

The interpretation of experimental data from novel mid-infrared few-cycle laser sources requires an understanding of ionization mechanisms and knowledge about related ion yields. Experimental studies have indicated sequential double ionization as the dominant process above 1014 W cm−2. These results contradict a recent prediction that in this spectral region, non-sequential processes dominate the double ionization of xenon up to intensities of about 1015 W cm−2. In either case, the ratio of doubly to singly charged xenon yield reported in previous studies has been limited to a few percent, indicating a regime well below the onset of saturation of the double ionization process. We present an experimental study of double ionization of xenon and krypton atoms exposed to intense near four-cycle pulses at 3.2 μm. Our experiments rely on the ion microscopy technique, which facilitates the detection of ions originating from a restricted region within the interaction volume, thereby reducing the impact of focal averaging. Our measurements suggest that at intensities of close to 1.2 × 1014 W cm−2, double ionization of xenon and krypton is already significantly saturated. In particular, we find a doubly to singly charged yield ratio of about 75 percent for xenon and 25 percent for krypton. We compare our results with the predictions of different models accounting for the effects of volume averaging and focal geometry. We find that in the deeply saturated regime of our experiment, the Perelomov–Popov–Terentyev theory significantly underestimates the observed double ionization yield.

The dynamics and the decay processes of inner-shell excited atoms are of great interest in physics, chemistry, biology, and technology. The highly excited state decays very quickly through different channels, both radiative and non-radiative. It is therefore a long-standing goal to study such dynamics directly in the time domain. Using few-cycle infrared laser pulses, we investigated the excitation and ionization of inner-shell electrons through laser-induced electron re-collision with the original parent ions and measured the dependence of the emitted x-ray spectra on the intensity and ellipticity of the driving laser. These directly re-colliding electrons can be used as the initiating pump step in pump/probe experiments for studying core-hole dynamics at their natural temporal scale. In our experiment we found that the dependence of the x-ray emission spectrum on the laser intensity and polarization state varies distinctly for the two kinds of atomic systems. Relying on our data and numerical simulations, we explain this behavior by the presence of different excitation mechanisms that are contributing in different ratios to the respective overall x-ray emission yields. Direct re-collision excitation competes with indirect collisions with neighboring atoms by electrons having "drifted away" from the original parent ion. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

We generate attosecond pulse train (APT) in argon driven by the high repetition rate (HR) laser of the extreme light infrastructure-attosecond light pulse source (ELI-ALPS), providing 100 kHz, 80 W, 1030 nm, 40 fs pulses from a fiber chirped-pulse amplification (fiber-CPA) laser system. Under the current operating conditions of the high harmonic generation beamline (HR-GHHG), we observed the average pulse duration to be 395 as measured using the technique of reconstruction of attosecond beating by interference of two-photon transitions. The beamline uses an annular-shape laser beam so that the main part of the driving laser co-propagating with the APT can be eliminated by reflection on a holey mirror. An additional 100 nm aluminum foil is used to filter out the remaining laser and the low order harmonics, allowing 2 pJ APT with a bandwidth from 25 eV to 50 eV to be transported to the target position where the APT interacts with matter. The implementation of the HR-GHHG beamline in ELI-ALPS delivering attosecond pulse trains at 100 kHz paves the way for time-resolved experiments in the infrastructure, especially those that involve rare events and coincidence analysis, both of which need high statistics.

High-field THz pulse generation by the interaction of high intensity femtosecond laser with aligned nanorods target have been investigated experimentally and theoretically which shows 13.8 times enhancement in THz pulse energy in ≤ 20 THz.

Here we numerically study the optimal switching of relativistic high harmonic generation mechanisms and show that careful experiments can be designed by choosing appropriate parameter space where one can generate intense attosecond pulses from laser-plasmas.

In laboratory experiments, strong magnetic fields at the boundary of a plasma can be generated by means of laser-wakefield acceleration, enabling the study of magnetization processes in scaled versions of astrophysical plasmas. The onset and evolution of magnetic fields in laboratory and astrophysical plasmas is determined by several mechanisms1, including instabilities2,3, dynamo effects4,5 and ultrahigh-energy particle flows through gas, plasma6,7 and interstellar media8,9. These processes are relevant over a wide range of conditions, from cosmic ray acceleration and gamma ray bursts to nuclear fusion in stars. The disparate temporal and spatial scales where each process operates can be reconciled by scaling parameters that enable one to emulate astrophysical conditions in the laboratory. Here we unveil a new mechanism by which the flow of ultra-energetic particles in a laser-wakefield accelerator strongly magnetizes the boundary between plasma and non-ionized gas. We demonstrate, from time-resolved large-scale magnetic-field measurements and full-scale particle-in-cell simulations, the generation of strong magnetic fields up to 10–100 tesla (corresponding to nT in astrophysical conditions). These results open new paths for the exploration and modelling of ultrahigh-energy particle-driven magnetic-field generation in the laboratory.

International audience; Spatial properties of high-order harmonic beams produced by high-intensity laser-matter interactions carry rich information on the physics of the generation process, and their detailed understanding is essential for applications of these light beams. We present a thorough study of these properties in the case of harmonic generation from plasma mirrors, up to the relativistic interaction regime. $In\ situ$ ptychographic measurements of the amplitude and phase spatial profiles of the different harmonic orders in the target plane are presented, as a function of the key interaction parameters. These measurements are used to validate analytical models of the harmonic spatial phase in different generation regimes, and to benchmark ultrahigh-order Maxwell solvers of particle-in-cell simulation codes.

Globally, large international research infrastructures have over many decades promoted excellence in science and technology. Aligned with the international practice, the Europe Strategy Forum for Research Infrastructures (ESFRI) has developed and keeps updating a roadmap for research infrastructures. The Extreme Light Infrastructure (ELI) is one of the two large scale Laser Research Infrastructures (RI) proposed in the ESFRI Roadmap published in 2006. ELI aims to provide access to some of the most intense world-wide lasers for the international scientific user community, as well as secondary radiation and particle sources driven by them, offering to the users new interdisciplinary research opportunities. ELI is currently implemented as a distributed infrastructure in three pillars: ELI-Beamlines (ELI-BL) in Dolni Břežany, Czech Republic, ELI-Attosecond Light Pulse Source (ELI-ALPS) in Szeged, Hungary and ELI-Nuclear Physics (ELI-NP) in Magurele, Romania. This chapter is devoted to introduce the Hungarian pillar, ELI-ALPS, which will be operational in Szeged in 2018, with the primary mission to provide to the users the highest laboratory spatiotemporal resolution and a secondary mission to contribute to the technological development towards 200 petawatt (PW) lasers for high-field science, which is the ultimate goal of the ELI project. The chapter includes descriptions of the primary and secondary sources, while emphasis is given to selected examples of the scientific case of ELI-ALPS, presenting unique access offered by the technologies to be hosted in the infrastructure.

International audience; Real-time observation of ultrafast dynamics in the microcosm is a fundamental approach for understanding the internal evolution of physical, chemical and biological systems. Tools for tracing such dynamics are flashes of light with duration comparable to or shorter than the characteristic evolution times of the system under investigation. While femtosecond (fs) pulses are successfully used to investigate vibrational dynamics in molecular systems, real time observation of electron motion in all states of matter requires temporal resolution in the attosecond (1 attosecond (asec) = 10(-18) s) time scale. During the last decades, continuous efforts in ultra-short pulse engineering led to the development of table-top sources which can produce asec pulses. These pulses have been synthesized by using broadband coherent radiation in the extreme ultraviolet (XUV) spectral region generated by the interaction of matter with intense fs pulses. Here, we will review asec pulses generated by the interaction of gas phase media and solid surfaces with intense fs IR laser fields. After a brief overview of the fundamental process underlying the XUV emission form these media, we will review the current technology, specifications and the ongoing developments of such asec sources.

Ion acceleration from intense (Iλ2 > 1018 Wcm−2 μm2) laser-plasma interaction is experimentally studied within a wide range of He gas densities. Focusing an ultrashort pulse (duration "Equation missing" ion plasma period) on a newly designed submillimetric gas jet system, enabled us to inhibit total evacuation of electrons from the central propagation channel reducing the radial ion acceleration associated with ponderomotive Coulomb explosion, a mechanism predominant in the long pulse scenario. New ion acceleration mechanism have been unveiled in this regime leading to non-Maxwellian quasi monoenergetic features in the ion energy spectra. The emitted nonthermal ion bunches show a new scaling of the ion peak energy with plasma density. The scaling identified in this new regime differs from previously reported studies.

International audience; ELI-ALPS, one of the three pillars of the Extreme Light Infrastructure (ELI) project, will be in a unique position to offer dedicated experimental platforms for ultrashort time-resolved investigations of strongly excited dynamical systems. The state-of-the-art surface plasma attosource (SPA) beamlines at ELI-ALPS are being designed and developed to enable new directions in plasma-based attoscience research. The SPA beamlines will be driven by ultrashort, high peak power, high repetition rate lasers based on the latest technology and are aimed to develop previously unavailable attoscience experimental platforms employing surface high-harmonic generation process. This endeavor involves research and development challenges and careful considerations. Here we discuss the physics of plasma attosources and their characteristics under such extreme conditions and the beamline functionalities that would facilitate these objectives. Finally, we delineate the initial research possibilities with these sophisticated instruments. (C) 2018 Optical Society of America

Accelerating particles to relativistic energies over very short distances using lasers has been a long standing goal in physics. Among the various schemes proposed for electrons, vacuum laser acceleration has attracted considerable interest and has been extensively studied theoretically because of its appealing simplicity: electrons interact with an intense laser field in vacuum and can be continuously accelerated, provided they remain at a given phase of the field until they escape the laser beam. But demonstrating this effect experimentally has proved extremely challenging, as it imposes stringent requirements on the conditions of injection of electrons in the laser field. Here, we solve this long-standing experimental problem for the first time by using a plasma mirror to inject electrons in an ultraintense laser field, and obtain clear evidence of vacuum laser acceleration. With the advent of PetaWatt class lasers, this scheme could provide a competitive source of very high charge (nC) and ultrashort relativistic electron beams., accepted to Nature Physics (as of Nov. 2015)

We explain how structuring femtosecond laser pulses in space and time leads to new effects in ultrahigh intensity laser plasma interactions, with three examples: ultrafast wavefront rotation, transient plasma gratings, and light springs.

International audience; The extreme intensities now delivered by femtosecond lasers make it possible to drive and control relativistic motion of charged particles with light1, opening a path to compact particle accelerators2, 3 and coherent X-ray sources4, 5. Accurately characterizing the dynamics of ultrahigh-intensity laser–plasma interactions as well as the resulting light and particle emissions is an essential step towards such achievements. This remains a considerable challenge, as the relevant scales typically range from picoseconds to attoseconds in time, and from micrometres to nanometres in space. In these experiments, owing to the extreme prevalent physical conditions, measurements can be performed only at macroscopic distances from the targets, yielding only partial information at these microscopic scales. This letter presents a major advance by applying the concepts of ptychography6, 7 to such measurements, and thus retrieving microscopic information hardly accessible until now. This paves the way to a general approach for the metrology of extreme laser–plasma interactions on very small spatial and temporal scales

We review the main research directions ongoing in the development of extreme ultraviolet sources based on high-harmonic generation for the synthesization and application of trains and isolated attosecond pulses to time-resolved spectroscopy. A few experimental and theoretical works will be discussed in connection to well-established attosecond techniques. In this context, we present the unique possibilities offered for time-resolved investigations on the attosecond timescale by the new Extreme Light Infrastructure Attosecond Light Pulse Source, which is currently under construction. (C) 2015 Published by Elsevier B.V.

We offer a new method to study the transport of fast electrons in dense, hot media. The technique relies on temporal profiling of the laser induced magnetic fields and offers a unique capability to map the hot electron currents and their neutralization (or lack of it) by the return currents in the plasma. We report direct quantitative measurements of strong electric inhibition in insulators and turbulence induced anomalous stopping of hot electrons in conductors.

We examine enhanced hard x-ray emission (20 - 200 keV) from plasmas produced on nanoparticles coated optically polished copper surface under different prepulse conditions. We observe that enhancement reduces with increasing prepulse intensity. The dynamics of the process is seen to be in the ps regime. We attribute this to preplasma formation on nanoparticles and subsequent modification/destruction of the nanostructure layer before the arrival of the main pulse. It is suggested that high-contrast ultrashort pulses are essential for nanoparticles to function as yield enhancers.

Journal of physics / B 50(13), 132002 - (2017). doi:10.1088/1361-6455/aa6ee8, This review presents the technological infrastructure that will be available at the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI-ALPS) international facility. ELI-ALPS will offer to the international scientific community ultrashort pulses in the femtosecond and attosecond domain for time-resolved investigations with unprecedented levels of high quality characteristics. The laser sources and the attosecond beamlines available at the facility will make attosecond technology accessible for scientists lacking access to these novel tools. Time-resolved investigation of systems of increasing complexity is envisaged using the end stations that will be provided at the facility., Published by IOP Publ., Bristol

International audience; A general approach for optically controlled spatial structuring of overdense plasmas generated at the surface of initially plain solid targets is presented. We demonstrate it experimentally by creating sinusoidal plasma gratings of adjustable spatial periodicity and depth, and study the interaction of these transient structures with an ultraintense laser pulse to establish their usability at relativistically high intensities. We then show how these gratings can be used as a “spatial ruler” to determine the source size of the high-order harmonic beams produced at the surface of an overdense plasma. These results open new directions both for the metrology of laser-plasma interactions and the emerging field of ultrahigh intensity plasmonics.

In this letter, we propose two techniques capable of spatio-temporally characterizing high-power femtosecond laser chains. We demonstrate a new implementation of SEA TADPOLE. To avoid the problems induced by the the significant spatial jittering of the focal spot on high-power laser chains, our setup is adapted to collimated beams. In addition, a fibered light source is also used to correct the phase fluctuations. This experimental setup allows identifying any spatiotemporal distortions such as the pulse front tilt for instance. In this paper, to the best of our knowledge, we present the very first spatio-temporal characterization done on a TW laser. However, a SEA TADPOLE measurement is not immediate since it requires scanning the beam over the two transverse dimensions which prevent us from studying the shot-to-shot laser fluctuations. This is why, we developed MUFFIN, a single-shot technique capable of spatio-temporally characterizing a laser pulse along its two transverse dimensions. First experimental results obtained with this technique are presented here.

The advent of ultrahigh-power femtosecond lasers creates a need for optical components suitable to handle ultrahigh light intensities. Due to the unavoidable laser-induced ionization of matter, these components will have to be based on a plasma medium. An archetype of such optical elements is a plasma mirror, created when an intense femtosecond laser pulse impinges on a solid target. It consists of a dense plasma, formed by the laser field itself, which specularly reflects the main part of the pulse. Plasma mirrors have major potential applications as active optical elements to manipulate the temporal and spatial properties of intense laser beams, in particular for the generation of intense attosecond pulses of light. We investigate the basic physics involved in the deformation of a plasma mirror resulting from the light pressure exerted by the ultraintense laser during reflection, by deriving a simple model of this fundamental process, which we validate both numerically and experimentally. The understanding of this deformation is essential for all future applications of plasma mirrors, especially for the generation of collimated attosecond beams. We show how its effect on the attosecond beam divergence can be mitigated by using the laser phase, thus providing crucial control for future applications in attosecond science., Comment: 18 pages, 7 figures