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We present a review on the use of X-ray detectors based on lithium fluoride crystals both for the determination of the parameters of the X-ray sources and for the recording of radiographic images obtained with them. The results are presented for experiments on a radiographic analysis of biological objects and inorganic structures based on an image obtained from the thermal radiation of a high-temperature laser-plasma source, coherent X-ray radiation of a plasma laser, and a free-electron laser, as well as the generation of higher harmonics of the optical laser radiation.

Both K-shell x-ray emission spectroscopy and fluorescence spectroscopy are well-accepted diagnostics for experimental studies of warm dense matter and hot dense matter (HDM). Until now, however, this diagnosis has been used for the study of dense matter with temperatures lower than 100 eV or with temperatures above 1 keV. In this work, we have demonstrated the possibility of using K-shell emission spectroscopy for an intermediate temperature range of 100s eV to study dense plasma. Here, we discuss an analysis of the HDM emission spectra of a solid-state copper with temperatures up to a few hundreds of electronvolts heated by laser-accelerated charged particles.

Density effects have great importance for studying the state of matter at high energy densities both for astrophysical and laboratory objects. At the moment, the question remains as to which model should be used for the description of the effect of ionization potential depression (IPD) in plasma with densities up to solid-state ones. Recent X-ray free-electron laser based researches claimed the adequacy of an early IPD model of Ecker and Kroll over the well-accepted model of Stewart and Pyatt, provided that these two models give significantly different predictions. Subsequent researches performed with optical lasers have received the opposite result. This work is intended to resolve the existing contradiction in conclusions of mentioned experiments. For the first time, the IPD effect for Si XIII ions of plasma generated by an ultrarelativistic optical laser pulse was described and quantified. We demonstrate the "disappearance" of electronic states up to the state with a principal quantum number of n = 4 (inclusively); the plasma density was varied from the critical to the near-solid one. A radiation-collision code PrismSPECT was used to distinguish different IPD models.

The interaction of femtosecond ultra-intense laser pulses with clusters increases absorption of the incident laser light compared with the interaction with solid targets and leads to enhanced generation of different quantum beams with unique parameters. Future investigations of such interaction urgently need detailed modeling and optimization of cluster parameters, for instance, in order to obtain the clusters with desired size, or some specific spatial configuration of the target etc. A numerical model of gas-cluster targets production by the nozzle flows of gases and binary mixtures is presented. Some previous results of the model utilization are summarized, and some new results are given. Techniques of experimental verification of the numerical results are discussed.

Acceleration of particles from the interaction of ultraintense laser pulses up to $5\ifmmode\times\else\texttimes\fi{}{10}^{21}\text{ }\text{ }\mathrm{W}\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$ with thin foils is investigated experimentally. The electron beam parameters varied with decreasing spot size, not just laser intensity, resulting in reduced temperatures and divergence. In particular, the temperature saturated due to insufficient acceleration length in the tightly focused spot. These dependencies affected the sheath-accelerated protons, which showed poorer spot-size scaling than widely used scaling laws. It is therefore shown that maximizing laser intensity by using very small foci has reducing returns for some applications.

The use of laboratory experiments as plasma creating sources is a valuable tool for understanding astrophysical observations. Recently plasma created through irradiation by lasers with relativistic intensities has been used to study effects of hot electrons and X-ray pumping on X-ray formation of multiply charged ions spectra. This paper discusses the formation of K-shell Fe spectra recorded from a plasma irradiated by 35 fs pulses with intensities of 1021 W/cm2. Modeling of the spectra suggests three different regions of plasma radiation including a cold ~10 eV region, a mild ~700 eV region, and a hot ~3500 eV region. The influence of hot electrons and X-ray pumping is discussed and a comparison with K-shell Fe spectra from a 1 MA X-pinch experiment is included to highlight the differences due to the shorter time frame of the laser–plasma interaction experiment.

A superbright X-ray source with a radiation temperature of ~1.2 keV making it possible to create a solid-state plasma whose kinetics is determined by the radiative processes has been implemented under the impact of a 170-TW pulse of the PEARL femtosecond laser facility on an aluminum target with submicron thickness. The diagnostics of the created plasma is performed by X-ray spectral methods using spectral transitions in hollow multicharged ions.

Direct metrology of coherent short-wavelength beamlines is important for obtaining operational beam characteristics at the experimental site. However, since beam-time limitation imposes fast metrology procedures, a multi-parametric metrology from as low as a single shot is desirable. Here a two-dimensional (2D) procedure based on high-resolution Fresnel diffraction analysis is discussed and applied, which allowed an efficient and detailed beamline characterization at the SACLA XFEL. So far, the potential of Fresnel diffraction for beamline metrology has not been fully exploited because its high-frequency fringes could be only partly resolved with ordinary pixel-limited detectors. Using the high-spatial-frequency imaging capability of an irradiated LiF crystal, 2D information of the coherence degree, beam divergence and beam quality factor M 2 were retrieved from simple diffraction patterns. The developed beam metrology was validated with a laboratory reference laser, and then successfully applied at a beamline facility, in agreement with the source specifications.

A combination of a petawatt laser and nuclear physics techniques can crucially facilitate the measurement of exotic nuclei properties. With numerical simulations and laser-driven experiments we show prospects for the Laser-driven Exotic Nuclei extraction–acceleration method proposed in [M. Nishiuchi et al., Phys, Plasmas 22, 033107 (2015)]: a femtosecond petawatt laser, irradiating a target bombarded by an external ion beam, extracts from the target and accelerates to few GeV highly charged short-lived heavy exotic nuclei created in the target via nuclear reactions.

The Spectr-W3 database was developed in 2001–2013 and is available online (http://spectrw3. snz.ru). The database contains information on various spectroscopic constants of atoms and ions such as the wavelengths and probabilities of radiative transitions, energy levels of atoms and ions, ionization potentials, autoionization rates, and the parameters of analytical approximation of cross sections and rates of collisional transitions in atoms and ions. Spectr-W3 presently contains around 450 thousand records and is the world’s largest factual database on spectral properties of multicharged ions. A new stage of development of Spectr-W3, which involves adding a new section titled “Emission Spectrograms” to the database, commenced in 2014. In contrast to the already existing sections that contain tabulated data, this new section provides graphical data (with necessary explanatory notes) on the spectrograms of emission of atoms and ions excited in various plasma sources. The structure of sections of the Spectr-W3 database is characterized, and examples of queries and the corresponding search results are given.

High power laser systems are an attractive driver for compact energetic ion sources. We demonstrate repetitive acceleration at 0.1 Hz of proton beams up to 40 MeV from a reeled tape target irradiated by ultra-high intensities up to 5 × 1021 Wcm − 2 and laser energies ≈ 15 J using the J-KAREN-P laser system. We investigate the stability of the source and its behaviour with laser spot focal size. We compare the scaling of proton energy with laser energy to a recently developed analytical model, and also demonstrate that it is possible to reach energies up to 50 MeV on a single shot with a lower laser energy ≈ 10 J by using a thinner target, motivating development of high repetition targetry suitable for thinner targets.

The two-temperature, 2D hydrodynamic code Hydro–ELectro–IOnization–2–Dimensional (HELIO2D), which takes into account self-consistently the laser energy absorption in a target, ionization, heating, and expansion of the created plasma is elaborated. The wide-range two-temperature equation of state is developed and used to model the metal target dynamics from room temperature to the conditions of weakly coupled plasma. The simulation results are compared and demonstrated a good agreement with experimental data on the Mg target being heated by laser pulses of the nanosecond high-energy laser for heavy ion experiments (NHELIX) at Gesellschaft fur Schwerionenforschung. The importance of using realistic models of matter properties is demonstrated.

By analyzing profiles of experimental x-ray spectral lines of Si XIV and Al XIII, we found that both Langmuir and ion acoustic waves developed in plasmas produced via irradiation of thin Si foils by relativistic laser pulses (intensities ~10sup21/supW/cmsup2/sup). We prove that these waves are due to the parametric decay instability (PDI). This is the first time that the PDI-induced ion acoustic turbulence was discovered by the x-ray spectroscopy in laser-produced plasmas. These conclusions are also supported by PIC simulations. Our results can be used for laboratory modeling of physical processes in astrophysical objects and a better understanding of intense laser-plasma interactions.

We present the progress on the upgrade status of the J-KAREN-P , which is a Ti: Sapphire laser aiming at the intensity of 1022 W/cm2 at the repetition rate of 0.1 Hz. The upgrade includes two pilot experiments in order to show the laser performance on target. The first experiment is to generate high-energy ions from thin-foil target. The second experiment is the high-order harmonic at a relativistic intensity. Currently, laser acceleration of protons is being tested and we have obtained 32 MeV protons from a 5-µm stainless steel target irradiated by a 14-J, 30-fs laser pulse. In addition, a joint program toward compact X-ray free-electron laser based on laser electron acceleration is presented briefly and the corresponding J-KAREN-P work is presented.

Summary In this paper, the use of lithium fluoride (LiF) as imaging radiation detector to analyse living cells by single-shot soft X-ray contact microscopy is presented. High resolved X-ray images on LiF of cyanobacterium Leptolyngbya VRUC135, two unicellular microalgae of the genus Chlamydomonas and mouse macrophage cells (line RAW 264.7) have been obtainedutilizingX-rayradiationinthewaterwindowenergy rangefromalaserplasmasource.Theusedmethodisbasedon loading of the samples, the cell suspension, in a special holder wheretheyareinclosecontactwithaLiFcrystalsolid-stateXrayimagingdetector.Afterexposureandsampleremoval,the imagesstoredinLiFbythesoftX-raycontactmicroscopytechniquearereadbyanopticalmicroscopeinfluorescencemode. The clear image of the mucilaginous sheath the structure of the filamentous Leptolyngbya and the visible nucleolus in the macrophage cells image, are noteworthiness results. The peculiaritiesoftheusedX-rayradiationandoftheLiFimaging detectorallowobtainingimagesinabsorptioncontrastrevealing the internal structures of the investigated samples at high spatialresolution.Moreover,thewidedynamicrangeoftheLiF imagingdetectorcontributestoobtainhigh-qualityimages.In particular, we demonstrate that this peculiar characteristic of LiF detector allows enhancing the contrast and reveal details even when they were obscured by a nonuniform stray light.

Ultrashort laser pulse is a unique nanometallurgical tool which operates at extreme conditions: ultimate strength of material, the smallest spatiotemporal scales, and nonequlibrium crystallization. Approaches to ultimate strength and to highly nonequlibrium crystallization are tightly coupled with the smallness of spatiotemporal scales. Usage of the tool opens new opportunities to create materials with enhanced surface hardness, anticorrosion properties, and diverted optical constants. To use these advantages we have first of all to develop clear and reliable physical model. The paper presents new results concerning interactions of optical or X-ray lasers with metals. It is shown that ultrashort laser pulse melts surface layer, sends shock into bulk, and foams molten metal. Dense dislocation bilayer is created thanks to fast recrystallization (the first sublayer) and plastic transformations behind strong shock (the second sublayer). Plastic shock generated at moderate laser intensities attenuates sharply during its propagation into metal. During this attenuation, a plastic shock regenerates into a powerful elastic shock. This process defines boundary between the second dislocation sublayer and undamaged solid. Mechanical breaking of foam after its strong stretching and fly away of a part of melt together with fast freezing are responsible for appearance of chaotic frozen nanostructures at an irradiated surface.

A high repetition rate scintillator-based transverse beam profile diagnostic for laser-plasma accelerated proton beams has been designed and commissioned. The proton beam profiler uses differential filtering to provide coarse energy resolution and a flexible design to allow optimisation for expected beam energy range and trade-off between spatial and energy resolution depending on the application. A plastic scintillator detector, imaged with a standard 12-bit scientific camera, allows data to be taken at a high repetition rate. An algorithm encompassing the scintillator non-linearity is described to estimate the proton spectrum at different spatial locations.

We present an overview of our systematic studies of the surface modifications resulting from the interactions of both single and multiple picosecond soft x-ray laser (SXRL) pulses with materials, such as gold (Au), copper (Cu), aluminum (Al), and lithium fluoride (LiF). We show experimentally the possibility of the precise nanometer size structures (~10–40 nm) formation on their surfaces by ultra-low (~10–30 mJ/cm2 ) fluencies of single picosecond SXRL pulse. Comparison experimental results with the atomistic model of ablation, which was developed for the single SXRL shot interaction with dielectrics and metals, is provided. Theoretical description of surface nanostructures is considered and is shown that such structures are formed after laser illumination in a process of mechanical spallation of ultrathin surface layer of molten metal. Spallation is accompanied by a strong foaming of melt, breaking of foam, and freezing of foam remnants. Those remnants form chaotic nanostructures, which are observed in experiments. Our measurements show that electron temperature of matter under irradiation of SXRL was lower than 1 eV. The model calculation also predicts that the ablation induced by the SXRL can create the significant low electron temperature. Our results demonstrate that tensile stress created in LiF and metals by short SXRL pulse can produce spallative ablation of target even for drastically small fluencies, which open new opportunities for material nano processing.

The shape of the X-ray pulse generated by picosecond laser plasma is experimentally studied. The unusual phenomenon was experimentally observed for the first time for targets made of moderate-heavy chemical elements, namely, the pulse of hard X-ray radiation generated by laser plasma at the laser radiation flux of ~1018 W cm-2 had a longer duration than the pulse of softer X-ray radiation. A simple kinetic model is suggested for explaining this fact. We have suggested a method for controlling the temporal shape of X-ray pulse emitted by laser plasma by varying the contrast of laser pulse.

It is proposed to use a high rate of collisional ionization in a superdense laser plasma to generate incoherent femtosecond X-ray pulses. The calculations indicate that the use of picosecond laser pulses with a contrast of about 1010 will allow the generation of an X-ray pulse with a duration of about 10 fs. The adequacy of the proposed model of the excitation of linear X-ray radiation from the plasma has been tested in the experiments with a picosecond laser of a moderately high contrast.

It was shown (Faenov et al., 2015b) that the energy of femtosecond laser pulses with relativistic intensity approaching to ~1021 W/cm2 is efficiently converted to X-ray radiation and produces exotic states in solid density plasma periphery. We propose and show by one-dimensional two-temperature hydrodynamic modeling, that applying two such unique ultra-bright X-ray sources with intensities above 1017 W/cm2 – allow to generate shock waves with strength of up to some hundreds Mbar, which could give new opportunities for studies of matter in extreme conditions.

N. J. Hartley, N. Ozaki, T. Matsuoka, B. Albertazzi, A. Faenov, Y. Fujimoto, H. Habara, M. Harmand, Y. Inubushi, T. Katayama, M. Koenig, A. Krygier, P. Mabey, Y. Matsumura, S. Matsuyama, E. E. McBride, K. Miyanishi, G. Morard, T. Okuchi, T. Pikuz, O. Sakata, Y. Sano, T. Sato, T. Sekine, Y. Seto, K. Takahashi, K. A. Tanaka, Y. Tange, T. Togashi, Y. Umeda, T. Vinci, M. Yabashi, T. Yabuuchi, K. Yamauchi, and R. Kodama , "Ultrafast observation of lattice dynamics in laser-irradiated gold foils", Appl. Phys. Lett. 110, 071905 (2017) https://doi.org/10.1063/1.4976541., We have observed the lattice expansion before the onset of compression in an optical-laser-driven target, using diffraction of femtosecond X-ray beams generated by the SPring-8 Angstrom Compact Free-electron Laser. The change in diffraction angle provides a direct measure of the lattice spacing, allowing the density to be calculated with a precision of ±1%. From the known equation of state relations, this allows an estimation of the temperature responsible for the expansion as

A new diagnosis method for high energy ions utilizing a single CR-39 detector mounted on plastic plates is demonstrated to identify the presence of the high energy component beyond the CR-39's detection threshold limit. On irradiation of the CR-39 detector unit with a 25 MeV per nucleon He ion beam from conventional rf-accelerators, a large number of etch pits having elliptical openings are observed on the rear surface of the CR-39. Detailed investigations reveal that these etch pits are created by heavy ions inelastically backscattered from the plastic plates. This ion detection method is applied to laser-driven ion acceleration experiments using cluster-gas targets, and ion signals with energies up to 50 MeV per nucleon are identified.

A short review of our experimental studies on generation of photon and particle beams in submicron clusters irradiated by intense, high-contrast (similar to 10(8-)10(10)) femtosecond laser pulses is presented. It is shown that highly-efficient laser-cluster interaction allows creating bright sources of X-ray, high-energy electron and ion beams. The examples of applications of femtosecond-laser-produced cluster plasmas (FLPCP) for X-ray and ion beams radiography are presented.

X-ray spectroscopic diagnostics of laser-cluster interaction at the stage of nonadiabatic scattering of clusters and formation of a spatially uniform plasma channel has been performed. The experimental investigations have been carried out on a Ti:Sa laser setup with a pulse duration of about 65 fs and an energy up to 600 mJ. It has been shown that, within 10 ps from the beginning of a laser femtosecond pulse, the laser-cluster interaction forms a uniform plasma channel with a length of 0.4 to 1 mm with the parameters N e ∼ 1019−1020 cm−3 and T e ∼ 100 eV.

It is shown that various spectroscopic methods based on measurements of X-ray spectra radiated from cluster targets can be used for estimation of the destruction degree of clusters by laser prepulses. These methods allow insight to be gained regarding the important issue of preservation of the dense cluster core at the moment of the arrival of the main laser pulse. In addition, they can be used for quantitative estimation of the size of the undestroyed parts of the clusters and also for measuring the temperature and density of the preplasmas produced by the laser prepulses.

Experiments with an ultrahigh-contrast femtosecond laser have yielded a new type of X-ray emission spectra with a complex structure consisting of resonance lines against the quasicontinuous background. Some recent work has shown that such spectra can only be accounted for by considering the radiation emitted by multiply charged hollow (empty K shell) ions in an ultradense plasma. This review discusses the observation of the spectra of hollow ions in an ultradense laser plasma and considers the types of such ions and how they are excited. Considerable opportunities of hollow ion spectra-based diagnostic techniques are emphasized.

The effects of self-absorption of X-ray spectral lines have been experimentally observed in the plasma of cluster targets. It has been shown that, since a cluster target is condensed in the femtosecond time scale and gaseous in the picosecond time scale, self-absorption effects can observed for X-ray spectral lines that are predominantly emitted during the action of a laser pre-pulse. The self-absorption effects are manifested as spectral lines with asymmetric profiles where the long-wavelength wing is suppressed compared to the short-wavelength wing. The observation of asymmetric contours is important for the diagnostics of the laser-cluster interaction because it enables the conclusion of whether the laser pre-pulse completely destroys the cluster and makes it possible to quantitatively estimate the size of the central region of the cluster, which has a solid-state density to the moment of the arrival of the main laser pulse.

Neutron imaging by color center formation in LiF crystals was applied to a sensitivity indicator (SI) as a standard samples for neutron radiography. The SI was exposed to a 5 mm pinhole-collimated thermal neutron beam with an LiF crystal and a neutron imaging plate (NIP) for 120 min in the JRR-3M thermal neutron radiography facility. The image in the LiF crystal was read out using a laser confocal microscope. All gaps were clearly observed in images for both the LiF crystal and the NIP. The experimental results showed that LiF crystals have excellent characteristics as neutron imaging detectors in areas such as high spatial resolution.

The interaction of radiation of a picosecond X-ray laser (wavelength λ = 13.9 nm) with targets made of a thick gold film has been studied theoretically and experimentally. It has been shown experimentally that the action of individual X-ray laser pulses with a fluence of F ≈ 21 mJ/cm2 initiates the nanostructuring of the gold surface. Explicitly taking into account the electron subsystem, we have proposed an atomistic model of ablation that makes it possible to adequately describe the experimental results. The atomistic simulation involves the ion-ion potential depending on the electron temperature T e . The use of such a potential makes it possible to take into account an increase in the pressure in the system with increasing T e and to reveal two laser ablation mechanisms.

A study is made of the ultra-short laser pulse irradiation of Ar cluster targets. Experiments have been performed with large cluster sizes and using very high laser contrasts, which have allowed clear and unambiguous observation of exotic inner-shell transitions in near-neutral Ar ions. The interaction of the main laser pulse with the unperturbed target is a necessary requirement for observing these lines. Our measurements are supported by kinetics calculations in which a very detailed atomic model is used. The calculations predict all of the spectral features found experimentally, and support the notion that the X-ray emission arises from many ion stages of the Ar plasma, from near-neutral through He-like ions, and from a range of plasma temperatures and densities.

Ultrashort X-ray laser pulse acts onto electron subsystem of dielectrics such as LiF and transfers matter into a two-temperature state with hot electrons excited by the pulse from valence to conduction band. Because of the small heat conduction, the hydrodynamic motion proceeds in adiabatic regime keeping the radiation attenuation depth Datt as the only scale of the spatial heat distribution. Hydrodynamic motion qualitatively changes with absorbed energy increase. At low fluences F ∼ 10mJ/cm 2 a spallative removal of LiF remaining in solid state takes place. This is a reason for the low ablation threshold. The paper presents new experimental findings supporting this conclusion. For the first time these findings are obtained using ultrashort extreme vacuum ultraviolet-free electron laser (EUV-FEL). In the case of high fluence, also achieved in our experiments at EUV-FEL, material removal happens as result of outflow of matter transferred into the gaseous state. This explains the slow growth of the amount of ablated mass with significant fluence increase.

Laser-matter interaction is defined by an electronic band structure of condensed matter and frequency ωL of electromagnetic radiation. In the range of moderate fluences, the energy absorbed by electrons from radiation finally thermalizes in the ion thermal energy. The thermalization processes are different for optical as compared with X-ray quanta and for metals relative to semiconductors and dielectrics, since the light absorption and electron-electron, electron-ion dynamics are sensitive to the electron population in a conduction band and the width of a forbidden gap. Although the thermalization processes are different, the final state is simply a heated matter. Laser heating creates powerful stresses in a target if duration of a laser pulse τL is short in acoustic time scale. Nucleation and material removal take place under such stresses. Such way of removal is called here the spallative ablation. Thus the spallative ablation is an ablation mechanism universally important for qualitatively different materials and quanta. c

X-ray diagnostics of the interaction of femtosecond laser pulses with intensities of 1016–1018 W/cm2 with CO2 clusters and frozen nanosize water particles is carried out. The stage of cluster expansion and the formation of a plasma channel, which governs the parameters of the formed X-ray radiation source and accelerated ion flows, is studied. The measurements are based on recording spatially resolved X-ray spectra of H- and He-like oxygen ions. Utilization of Rydberg transitions for spectra diagnostics makes it possible to determine plasma parameters on a time scale of t ∼ 10 ps after the beginning of a femtosecond pulse. The role of the rear edge of the laser pulse in sustaining the plasma temperature at a level of ∼100 eV in the stage of a nonadiabatic cluster expansion is shown. The analysis of the profiles and relative intensities of spectral lines allows one to determine the temperature and density of plasma electrons and distinguish the populations of “thermal” ions and ions that are accelerated up to energies of a few tens of kiloelectronvolts. It is shown that the use of solid clusters made of frozen nanoscale water droplets as targets leads to a substantial increase in the number of fast He-like ions. In this case, however, the efficiency of acceleration of H-like ions does not increase, because the time of their ionization in plasma exceeds the time of cluster expansion.