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We present an indirect method of estimating the strength of a shock wave, allowing on line monitoring of its reproducibility in each laser shot. This method is based on a shot-to-shot measurement of the X-ray emission from the ablated plasma by a high resolution, spatially resolved focusing spectrometer. An optical pump laser with energy of 1.0 J and pulse duration of ∼660 ps was used to irradiate solid targets or foils with various thicknesses containing Oxygen, Aluminum, Iron, and Tantalum. The high sensitivity and resolving power of the X-ray spectrometer allowed spectra to be obtained on each laser shot and to control fluctuations of the spectral intensity emitted by different plasmas with an accuracy of ∼2%, implying an accuracy in the derived electron plasma temperature of 5%-10% in pump-probe high energy density science experiments. At nano- and sub-nanosecond duration of laser pulse with relatively low laser intensities and ratio Z/A∼0.5, the electron temperature follows Te∼Ilas2/3. Thus, measurements of the electron plasma temperature allow indirect estimation of the laser flux on the target and control its shot-to-shot fluctuation. Knowing the laser flux intensity and its fluctuation gives us the possibility of monitoring shot-to-shot reproducibility of shock wave strength generation with high accuracy. [ABSTRACT FROM AUTHOR]

A short review of our experimental studies on generation of photon and particle beams in submicron clusters irradiated by intense, high-contrast (∼ 108-1010) femtosecond laser pulses is presented. It is shown that highlyefficient 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. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

It has been shown that a femtosecond plasma of cluster targets is an almost isotropic source of fast ions and, hence, can be used to obtain ionographic images with a wide field of view. The spatial resolution of the resulting ionographic images is no worse than 600 nm, which corresponds to a uniquely high value of about 105 of the ratio of the field of view to the resolution. The use of 100–300-keV ion fluxes ensures the sensitivity of the method to the sample thickness of no worse than 100 nm even for samples consisting of light chemical elements (C, H). The proposed method can be used to obtain images of low-contrast biological objects, thin films, membranes, and other nanostructured objects. [ABSTRACT FROM AUTHOR]

The interaction of femtosecond laser pulses with SiO2 aerogel targets has been analyzed by x-ray spectroscopic methods. The use of an aerogel target with transparent grains makes it possible to considerably reduce the requirements on laser-pulse contrasts for which heating occurs without the formation of a preplasma. A nanoplasma with a density sevenfold higher than the solid-state density has been detected. © 2004 MAIK “Nauka/Interperiodica”. [ABSTRACT FROM AUTHOR]

We report the attempt to prepare free-standing spherically bent Si crystals with radii of curvature as small as 30 cm and large uniform working areas up to several cm². We also report on the use of these crystals in the Laue geometry to record two-dimensional high spatial resolution x-ray images in the hard x-ray region (λ∼0.5 Å). We discuss how these bent crystals were made, and show how these spherically bent crystals were used in the Laue geometry to obtain hard x-ray images of test objects at the silver K-alpha wavelength at two different magnifications. The mean spatial resolution of this x-ray imaging scheme, determined from the recorded image traces, was found to be better than 10 µm over a field of view of 1.5×1.5 mm. Contributions of possible focusing mechanisms (dynamical and polychromatic) are discussed. Additional theoretical understanding of how such a scheme is working is needed. [ABSTRACT FROM AUTHOR]

Line emission spectrum of a laser plasma produced in an argon cluster jet target was measured on the n[sup 1]P[sub 1]–1[sup 1]S[sub 0](n=5–9) transitions of the helium-like Ar XVII ion for a pulse duration varying from 45 fs to 1.1 ps and a constant fluence of ∼10[sup 5]J/cm[sup 2]. The independent modeling of the relative intensities of the transitions from the n = 5, ..., 10 levels, as well as of the 2[sup 1]P[sub 1]–1[sup 2]S[sub 0] and 2[sup 3]P[sub 1]–1[sup 2]S[sub 0] lines and dielectronic satellites indicates that the electron temperature is anomalously low and that the electron density in emitting plasma increases with shortening the laser pulse. The excitation from the ground state by a small fraction of hot electrons is expected to be the main channel of populating the Ar XVII levels. © 2001 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

An intense isotropic source of multicharged carbon and oxygen ions with energy above 300 keV and particle number >108 per shot was obtained by femtosecond Ti:Sa laser irradiation of submicron clusters. The source was employed for high-contrast contact ionography images with 600 nm spatial resolution. A variation in object thickness of 100 nm was well resolved for both Zr and polymer foils. [ABSTRACT FROM AUTHOR]

High resolution X-ray imaging is crucial for many high energy density physics (HEDP) experiments. Recently developed techniques to improve resolution have, however, come at the cost of a decreased field of view. In this paper, an innovative experimental detector for X-ray imaging in the context of HEDP experiments with high spatial resolution, as well as a large field of view, is presented. The platform is based on coupling an X-ray backligther source with a Lithium Fluoride detector, characterized by its large dynamic range. A spatial resolution of 2 µm over a field of view greater than 2 mm2 is reported. The platform was benchmarked with both an X-ray free electron laser (XFEL) and an X-ray source produced by a short pulse laser. First, using a non-coherent short pulse laser-produced backlighter, reduced penumbra blurring, as a result of the large size of the X-ray source, is shown. Secondly, we demonstrate phase contrast imaging with a fully coherent monochromatic XFEL beam. Modeling of the absorption and phase contrast transmission of X-ray radiation passing through various targets is presented. [ABSTRACT FROM AUTHOR]

Nowadays charged-coupled device (CCD) detectors are widely used for the registration of multicharged ions x-ray spectra. These spectra are generated in a plasma during interaction of ultrashort, ultraintense laser pulses with solid targets. Strong parasitic radiation from the plasma affects CCD detectors and contaminates resulting spectra, so that spectral features can be completely covered by noise even during measurements with a very short accumulation time. In this work we propose a “mean to median” (M2M) algorithm for noise suppression in femtosecond laser plasma x-ray spectra. Series of spectra is necessary for the identification of corrupted data points by the developed method. The algorithm was tested with model spectra which reflect main features of experimental data. In practice we used it for extracting information about spectral lines of Ne-like Fe ions and He-like Al ions which allowed us to calculate plasma parameters. It is demonstrated that M2M method is able to clean spectra with more than 10% of corrupted pixels. Fluctuations in intensity of spectral lines induced by laser instability do not affect validity of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, we present the effects of a radiative shock (RS) on the morphology of jet-like objects subjected to hydrodynamic instabilities. To this end, we used an experimental platform developed to create RSs on high energy laser facilities such as LULI2000 and GEKKO XII. Here, we employed modulated targets to initiate Richtmyer–Meshkov and Rayleigh–Taylor instability (RTI) growth in the presence of an RS. The RS is obtained by generating a strong shock in a dense pusher that expands into a low-density xenon gas. With our design, only a limited RTI growth occurs in the absence of radiative effects. A strongly radiative shock has opposite effects on RTI growth. While its deceleration enhances the instability growth, the produced radiations tend to stabilize the interfaces. Our indirect experimental observations suggest a lower instability growth despite the interface deceleration. In addition, the jets, produced during the experiment, are relevant to astrophysical structures such as Herbig–Haro objects or other radiatively cooling jets. [ABSTRACT FROM AUTHOR]

Experimental and theoretical investigations of aluminum (Al) and gold (Au) surface modification by soft X-ray laser pulse are presented. Well-polished samples of Al and Au are irradiated by ps-duration pulse with wavelength of 13.9 nm at the energy range of 24-72 nJ. Differences in the melting and the ablation processes for those materials are observed. It is shown that at low laser pulse energy, the nanoscale ripples on the surface may be induced by melting without following ablation. In that case, the nanoscale changes in the surface are caused by splash of molten metal under gradient of fluence. At higher laser pulse energy, the ablation process occurs and craters are formed on the surface. However, the melting determines the size of the modified surface at all ranges of the laser energies. For interpretation of experimental results, the atomistic simulations of melting and ablation processes in Al and Au are provided. The calculated threshold fluencies for melting and ablation are well consistent with measured ones. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Differences between X-ray argon clusters excited at the laser-cluster and laser-droplet interactions have been analyzed. X-ray spectral methods have been proposed to determine the parameters of the appearing plasma at the early stages of its evolution. It has been shown that the spectra of hollow ions are the most informative in the first moments of the heating of a cluster, whereas the diagnostics of the late stages can be performed using the conventional lines of multicharged ions. [ABSTRACT FROM AUTHOR]

Abstract: 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 5mm pinhole-collimated thermal neutron beam with an LiF crystal and a neutron imaging plate (NIP) for 120min 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. [Copyright &y& Elsevier]

Abstract: Demonstration of neutron imaging by color center formation in LiF crystals is reported. Neutron radiography images of various objects, including thin Au wires, Cd plates, Gd plates and thin liquid tubes, have been recorded. The data show that neutron imaging with LiF has many excellent properties: high spatial resolution of 5.4μm, little granular noises, good linearity and large dynamic range. The high resolution neutron imaging with LiF will be useful for various applications such as quantitative characterizations of neutron sources and electric devices, comprising of low-Z elements such as Li-ion batteries and fuel cells. [ABSTRACT FROM AUTHOR]

The possibility of phase-contrast imaging of nanostructures has been analyzed with the use of a femtosecond-laser plasma as a spatially coherent soft x-ray source and a LiF crystal as an x-ray detector having both the submicron spatial resolution in a wide field of view and a high contrast. It is demonstrated that the spatial coherence length of radiation in the wavelength range 1–13 nm at a distance of 30 cm from the femtosecond-laser plasma source is ≃1.5 μm. The achieved spatial coherence of the source is sufficient to obtain high-quality phase-contrast x-ray images of foils with various chemical compositions and a thickness of ≃100 nm. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

X-ray spectra from Teflon targets irradiated by laser pulses with a duration of 60 fs to 1 ps have been investigated experimentally. It is shown that, when the contrast of the laser pulse is sufficiently low, the effect of self-focusing of the main laser pulse in the plasma produced by the prepulse can significantly enhance the generation efficiency of fast particles. In this case, ions with energies as high as ∼1 MeV are observed at relatively low laser intensities, q las ≈ (4–6) × 1016 W/cm2. [ABSTRACT FROM AUTHOR]

Satellite lines caused by radiative transitions from the Rydberg autoionization states of a Li-like Mg X ion in a plasma heated by radiation from a XeCl and a Nd laser are identified for the first time, and their wavelengths are measured precisely. Comparison of the experimental data with the atomic structures calculated by the method of relativistic perturbation theory shows that the accuracy of calculations of the energy of autoionization states is rather high even without the use of any semiempirical corrections and is of the order of 0.06%. The experimentally measured wavelengths can be used for a semiempirical estimate of the value of the leading order of perturbation theory among the orders that were neglected in calculations. It is shown that the simulation of the population kinetics of Rydberg autoionization states of Li-like ions in a dense plasma should take into account all possible channels of dielectronic capture, in particular, from the excited states of a He-like ion. The precision experimental wavelengths obtained for satellites of the He[sub β] and He[sub γ] lines of the Mg XI ion make possible to use these satellites as reference lines in studies of complicated spectra of multielectron ions. [ABSTRACT FROM AUTHOR]

It is shown that in a dense, not very hot, multiply charged plasma the satellite structures of resonance lines can become more intense than the resonance lines themselves. Experimental and theoretical investigations show that the conditions under which the satellite structures dominate in the emission spectrum of the plasma are quite easily realized experimentally and, furthermore, apparently they will be the most typical case in investigations of compressed plasma regions in inertial-confinement fusion experiments and in the study of plasma produced by high-contrast pico- and femtosecond laser pulses. © 1997 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The intense soft x-ray light source using the supersonic expansion of the mixed gas of He and CO2, when irradiated by a femtosecond Ti:sapphire laser pulse, is observed to enhance the radiation of soft x-rays from the CO2 clusters. Using this soft x-ray emissions, nanostructure images of 100-nm-thick Mo foils in a wide field of view (mm2 scale) with high spatial resolution (800 nm) are obtained with high dynamic range LiF crystal detectors. The local inhomogeneities of soft x-ray absorption by the nanometer-thick foils is measured with an accuracy of less than ±3%. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The response of lithium fluoride (LiF) crystal detectors to monochromatic X-rays is measured in the multi-kilo-electron-volt range. This response, as a function of the X-ray dose, is independent of photon energy with no saturation level found. The response, as a function of the incident energy flux, is found to increase for photons of lower energy due to the differing attenuation lengths of X-ray photons within the crystal. Small differences are seen between different confocal microscopes used to scan the data, suggesting the need for absolute calibration. The spatial resolution of the LiF is also measured (1.19–1.36 μm) and is found to be independent of incident photon energy. Finally, a photometric study is performed in order to assess the feasibility of using these detectors at current X-ray free electron laser and laser facilities worldwide. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The possibility of using the relative intensities of the 1 snp P-1 s S0 transitions with n = 3-6 in He-like multicharged ions to diagnose plasma in a nonstationary ionization state is considered. The calculations performed for F VIII ions show that, at electron temperatures of T = 10-100 eV, the intensity ratios are sensitive to the plasma electron density in the range of N = 10-10 cm. The universal calculated dependences can be used to diagnose various kinds of recombining or ionizing plasmas containing such ions. [ABSTRACT FROM AUTHOR]

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 M2 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, we detail the diagnostic technique used to infer the spatially resolved electron temperatures and densities in experiments dedicated to investigate the generation of magnetically collimated plasma jets. It is shown that the relative intensities of the resonance transitions in emitting He-like ions can be used to measure the temperature in such recombining plasmas. The intensities of these transitions are sensitive to the plasma density in the range of 1016-1020cm-3 and to plasma temperature ranges from 10 to 100 eV for ions with a nuclear charge Zn~10. We show how detailed calculations of the emissivity of F VIII ions allow to determine the parameters of the plasma jets that were created using ELFIE ns laser facility (Ecole Polytechnique, France). The diagnostic and analysis technique detailed here can be applied in a broader context than the one of this study, i.e., to diagnose any recombining plasma containing He-like fluorine ions. [ABSTRACT FROM AUTHOR]

The Spectr-W 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-W 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-W, 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-W database is characterized, and examples of queries and the corresponding search results are given. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The investigation of a recombining laser plasma is topical primarily because it can be used to simulate the interaction between plasma jets in astrophysical objects. It has been shown that the relative intensities of transitions of a resonance series of He-like multicharged ions can be used for the diagnostics of the recombining plasma. It has been found that the intensities of the indicated transitions for ions with the nuclear charge number Z ~ 10 are sensitive to the plasma density in the range N ~ 10-10 cm at temperatures of 10-100 eV. The calculations performed for the F VIII ion have determined the parameters of plasma jets created at the ELFIE nanosecond laser facility (Ecole Polytechnique, France) in order to simulate astrophysical phenomena. The resulting universal calculation dependences can be used to diagnose different recombining plasmas containing helium-like fluorine ions. [ABSTRACT FROM AUTHOR]

This paper describes an overview of our recent discovery – clear demonstration that LiF crystals can be efficiently used as a high-performance neutron imaging detector based on optically stimulated luminescence of color centers generated by neutron irradiation. It is shown that the neutron images we have obtained are almost free from granular noise, have a spatial resolution of ${\sim}5.4~{\rm\mu}\text{m}$ and a linear response with a dynamic range of at least $10^{3}$. The high contrast and good sensitivity of LiF crystals allow us to distinguish two holes with less than 2% transmittance difference. We propose to use such detectors in areas where high spatial resolution with high image gradation resolution is needed, including diagnostics of different plasma sources such as laser and z-pinch produced plasmas. [ABSTRACT FROM AUTHOR]

Spatial structures of ablative mass flow produced by femtosecond laser pulses are studied. In experiments with a gold film, the Ti:sapp laser pulse having a focal size of 100 microns on a target was used, while a soft X-ray probe pulse was utilized for diagnostics. The experimental data are compared with simulated mass flows obtained by two-temperature hydrodynamics and molecular dynamics methods. Simulation shows evolution of a thin surface layer pressurized after electron-ion thermalization, which leads to melting, cavitation and formation of spallation liquid layer. The calculated asymptotic surface velocity of this layer as a function of fluence is in reasonably good agreement with experimental data. [ABSTRACT FROM AUTHOR]

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 obtained utilizing X-ray radiation in the water window energy range from a laser plasma source. The used method is based on loading of the samples, the cell suspension, in a special holder where they are in close contact with a LiF crystal solid-state X-ray imaging detector. After exposure and sample removal, the images stored in LiF by the soft X-ray contact microscopy technique are read by an optical microscope in fluorescence mode. 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 peculiarities of the used X-ray radiation and of the LiF imaging detector allow obtaining images in absorption contrast revealing the internal structures of the investigated samples at high spatial resolution. Moreover, the wide dynamic range of the LiF imaging detector contributes to obtain high-quality images. 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. [ABSTRACT FROM AUTHOR]

Almost fully stripped Fe ions accelerated up to 0.9 GeV are demonstrated with a 200 TW femtosecond high-intensity laser irradiating a micron-thick Al foil with Fe impurity on the surface. An energetic low-emittance high-density beam of heavy ions with a large charge-to-mass ratio can be obtained, which is useful for many applications, such as a compact radio isotope source in combination with conventional technology. [ABSTRACT FROM AUTHOR]