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It is shown that the production of X-ray emission spectra in the interaction of high-intensity laser radiation with cluster tar- gets may be affected by the bichromatic oscillating electric field arising from the generation of the second harmonic of laser radia- tion. A technique is proposed for diagnosing harmonic generation in laser – cluster interactions using the spectral line profiles of multi- ply charged helium ions. The efficiency of second harmonic genera- tion at a laser intensity of 3 × 1018 W cm–2 is shown to amount to about 2 %.

Study of warm dense matter remains a very important task for understanding of many unique phenomena observing as in astrophysical research as in inertial fusion and fast ignition. In this work, we studied the parameters of plasma created by 1.7 ps laser pulses of relativistic intensity of 7 × 1018W/cm2in a specially designed Al–Cu wire-shape target, in comparison with a flat Cu and Al foil targets. We observed the strong emission of neutral or virtually neutral CuKαline from both Cu foil and Cu wire part of targets, which indicates the creation of a dense state exposed to the intense flow of hot electrons. Parameters of the plasma were evaluated by comparison of experimental spectra with the results of modeling by collisional-radiative kinetic code PrismSpec under the plasma zone approach. The using of Al foil in front of Cu wire part of target allowed avoiding the direct heating of Cu-wire and acquiring spectra of Cu K-shell emission evidently belonging to emission of warm dense matter (WDM) state. The upper estimate for the electron temperature in WDM region was found to be below 80 eV.

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.

International audience; During the last ten years, the ability of high power lasers to generate high energy density shocks has made them a reliable tool to study extreme states of matter. These states of matter are relevant in many important physics areas such as astrophysics, planetology and ICF physics. Here, we present some representative studies performed by using a driven laser shock: melting of iron at pressures relevant for geophysics, developments of new techniques to measure the density of highly compressed matter and a study of a radiative shock.

X-ray spectral lines of multicharged ions in a solid target interacting with picosecond laser pulses of moderate intensity (~3 × 1017 W cm−2) were measured on the 'Neodim' laser facility. Strong modulations in x-ray Lyα line profiles of hydrogen-like fluorine ions were observed, evidencing the presence of intense plasma oscillations with an amplitude of the electric field larger than 108 V cm−1 and a frequency of about 1015 s−1.

X-ray reflectivity curves at 20 keV photon energy of alpha-quartz spherically curved crystals have been measured using a micrometric synchrotron beam at the ESRF BM5. Six thin quartz crystals samples with curvature radii of 150 and 250 mm have been studied. Experimental results are compared with diffraction profile calculations using a lamellar model and a good agreement is found.

We report the observation of the sub-milliradiant divergence operation of a capillary discharge soft-X-ray laser, that indicates that X-ray radiation has been amplified in a refraction-guiding plasma active medium. The lasing is produced on the 46.9 nm transition of the Ne-like Ar. The 0.7 mrad divergence, axially peaked-profile beam is obtained in the single-pass amplification regime. The comparison of the recorded laser beam profiles with the results of our computer simulations shows that the capillary discharge z-pinch forms an active plasma wave guide, which has the electron density profile with depression on its axis. The waveguiding of X-ray radiation and its amplification is demonstrated over a 30 cm long plasma column, where the laser operates in a saturated regime with energy of ~ 50 μJ.

Stable color center production in lithium fluoride crystals has been applied to single-shot high-spatial-resolution imaging of a 2 ns long, 46.9 nm capillary discharge soft-X-ray laser pulse. Images of the unfocused beam and of the beam focused by a multi-layer mirror were recorded. The LiF crystal sensitivity was sufficient to impress high-contrast photo-luminescent patterns with single-pulse irradiation on an area up to 40 mm2. Interference fringes due to the soft-X-ray laser coherence were observed. The results demonstrate the potential of LiF crystals and films as a sub-micrometer resolution two-dimensional imaging tool for single-shot soft-X-ray laser applications.

We have observed spectra of highly charged zinc ions from a variety of laser-produced plasmas. High-precision measurements of transition wavelengths have been made in the range 6.7–8.6 A, with accuracies of ≈1 mA. Line identifications for high-n transitions (n ≤ 7) in the N-, O-, and F-like spectra of Zn XXIV, XXIII, XXII, respectively, are made by comparison with steady-state collisional–radiative models.

We report about nonlinear growth of x-ray emission intensity emitted from plasma generated by femtosecond petawatt laser pulses irradiating stainless steel foils. X-ray emission intensity increases as ~ I 4.5 with laser intensity I on a target. High spectrally resolved x-ray emission from front and rear surfaces of 5 μm thickness stainless steel targets were obtained at the wavelength range 1.7–2.1 A, for the first time in experiments at femtosecond petawatt laser facility J-KAREN-P. Total intensity of front x-ray spectra three times dominates to rear side spectra for maximum laser intensity I ≈ 3.2×1021 W/cm2. Growth of x-ray emission is mostly determined by contribution of bremsstrahlung radiation that allowed estimating bulk electron plasma temperature for various magnitude of laser intensity on target.

Spectra in the 7.50-8.70???range from highly charged copper ions are analysed, and line identifications are made for the Na-, Ne-, F- and O-like charge states. The spectra are recorded with a spherically bent crystal spectrometer using either a mica or quartz crystal for moderate (?/?? = 3000) and high (?/?? = 8000) energy resolution, respectively. The plasmas from which the spectra are emitted are formed with either a Nd:glass (15?ns pulse) or a XeCl (12?ns pulse) laser. Systematic variations in the observed spectra with pulse energy are studied. Using different laser energies, and defocusing of the laser to reduce the intensity, we create plasmas with different ionization state distributions, which allows us to deconvolve blended lines from different copper ions. Line identifications are made based on relativistic atomic structure calculations that account for configuration interaction in level energies and transition rates. We use full kinetics simulations of ion emissivities, not just calculations of theoretical transition energies, to identify the strong and weak lines in crowded spectral regions. We identify 2p-n? transitions for Ne-like Cu19+ for 4?n?8 and 2s-np transitions for 4?n?6. We offer the first identification of high-n (n?8) Na-like satellites to Ne-like Rydberg resonance lines. The first and second ionization energies for Cu19+ are found, at 1689.02 and 1709.16?eV, respectively, based on our observations.

The wavelengths of the 1snp 1P10-1s2 1S0 transitions in the He-like Mg XI (n = 4-9) and F VIII (n = 4-8) have been measured in laser-produced plasmas. The accuracy of the present measurements (0.4-1.6 mA) is a large improvement over previous results. The Rydberg series is used to determine the ground-state ionization energy of F VIII and Mg XI: Eion (F VIII) = 953.96±0.11 eV, Eion (Mg XI) = 1761.88±0.15 eV. These experimental results are compared with theoretical data calculated by the 1/Z-expansion method and the HFR and MCDF approaches. Fairly good agreement between theory and experiment is observed with a precision up to 5×10-5. Radiative corrections to the 1s2 1S0 state are analysed and compared with experiments. It is found that QED corrections to the ground-state ionization energy are significant at the present level of experimental accuracy.

Intra-Stark spectroscopy (ISS) is the spectroscopy within the quasistatic Stark profile of a spectral line. The present paper advances the ISS-based study of the relativistic laser–plasma interaction from our previous paper (Oks et al 2017 Opt. Express 25 1958). By improving the experimental conditions and the diagnostics, it provides an in-depth spectroscopic study of the simultaneous production of the Langmuir waves and of the ion acoustic turbulence at the surface of the relativistic critical density. It demonstrates a reliable reproducibility of the Langmuir-wave-induced dips at the same locations in the experimental profiles of Si XIV Ly-beta line, as well as of the deduced parameters (fields) of the Langmuir waves and ion acoustic turbulence in several individual 1 ps laser pulses and of the peak irradiances of 1–3 × 1020 W cm−2. Besides, this study employs for the first time the most rigorous condition of the dynamic resonance, on which the ISS phenomenon is based, compared to all previous studies in all kinds of plasmas in a wide range of electron densities. It shows how different interplays between the Langmuir wave field and the field of the ion acoustic turbulence lead to distinct spectral line profiles, including the disappearance of the Langmuir-wave-induced dips.

The X-ray spectra of multiply charged ions were recorded from planar agar (C12H18O9)n based targets with an average density of 2 mg cm-3 irradiated by high-power laser pulses (λ=1.054 μm, τ=2.5 ns, I ≈ 5 ×1013 W cm-2). The spectra were recorded with a high spectral and spatial resolution employing spherically bent (focusing) crystals of mica and quartz. An analysis of the experimental data obtained by the irradiation of Al2O3-doped agar samples allowed us to determine the main parameters of the plasma produced inside the targets. The ion temperature of plasma in low-density porous targets was estimated for the first time to be 1.5 — 2 times higher than the electron temperature.

The first observation of x-ray emission spectra of multiply charged ions in the plasma produced by a 35-fs laser pulse with an intensity up to 1017 W cm-2 in CO2 and Kr gas jet targets is reported. The emission in the wavelength ranges of the 1snp—1s2(n=3–6) transitions of O VII ions and the Lyα line of O VIII ions, as well as of the (2s1/22p63p3/2)1—2s22p6 1S0 and (2s1/22p63p1/2)1—2s22p6 1S0 lines of Ne-like KrXXVII ions testifies that the highly ionised plasma is formed by collision processes in clusters. Modelling the shape of the spectral lines of oxygen ions by including the principal mechanisms of broadening and absorption in optically dense plasmas reveals that the main contribution to the time-integrated intensity is made by the plasma with the parameters Ne=(2–20)×1020 cm-3 and Te=100 — 115 eV.

Complex spectral structures located between the resonance lines of H- and He-like MgXII and MgXI ions were recorded in experiments on plasma heating by the radiation of a low-power short-wavelength excimer XeCl laser (12-ns pulses with an energy of 2 J). The above spectral structures were shown to arise from transitions in the so-called hollow multicharged ions, i.e., in ions with an empty 1s-shell, which were previously observed in laser produced plasmas only with ultrahigh-power femto- and picosecond laser facilities having extremely high-contrast laser pulses.

A plasma of argon produced with a plasma focus discharge has been observed between 3.8 and 4.2 A. Spectra registered with a spectral resolution of 0.03 A/mm show satellite lines of Ar which were measured and compared with two independent theoretical calculations. Seven transitions of Li-like, eleven of Be-like. twelve of B-like, twenty of C-like, nine of N-like, seven of O-like and two of F-like argon have been identified. The agreement between the observations and the calculations and also between the two sets of calculations is generally good.

The combination of a table-top laser produced plasma X-ray source and a spherically bent crystal for the soft X-ray region is used in traditional X-ray microscopy schemes. The X-ray source is well localized both spatially ( ~ 20µm) and temporally ( ~ 1ps) and is spectrally tunable in a relatively wide range (6–14A). High quality monochromatic (δλ/λ ~ 10-5–10-4) images with high spatial resolution (up to ~ 4µm) and in a large field of view (few mm) are presented. For many applications, this low-cost compact system can offer a simple alternative to the larger installations, which are usually used. The spherically bent crystals can be used in a wide range of reflection angles, thus allowing wavelength selection.

For the first time registration of high-resolution soft x-ray emission and atomic data calculations of hollow-atom dielectronic satellite spectra of highly charged nitrogen have been performed. Double-electron charge-exchange processes from excited states are proposed for the formation of autoionizing levels in high-intensity laser-produced plasmas, when field-ionized ions penetrate into the residual gas. Good agreement is found between theory and experiment. Plasma spectroscopy with hollow ions is proposed and a temperature diagnostic for laser-produced plasmas in the long-lasting recombining regime is developed.

Emission spectra of multicharged xenon ions produced by a laser gas puff are observed with high spectral resolution in the 8.5-9.5 and 17- wavelength ranges. Three different theoretical methods are employed to obtain 3l- ( to 10) wavelengths and Einstein coefficients for Ni-like . For the 3d-4p transitions, very good agreement is found between the experimental wavelengths and the various theoretical wavelengths. These accurate energy level measurements can be useful for studying the Ni-like xenon x-ray laser scheme. On the other hand, several intense spectral lines could not be identified as 3l- lines of Ni-like xenon, despite the very good agreement between the wavelengths and Einstein coefficients calculated for these transitions using the three different methods.

On the basis of experimental and theoretical investigations it is demonstrated for the first time that in cold dense optically thick laser-produced plasmas, created near the target surface, the capture into the He-like ground state is negligible for line formation and that observed high-intensity -Rydberg satellite intensities are correlated with highly populated He-like excited states . X-ray emission spectra with simultaneous high spectral and spatial resolution provide a direct verification of the proposed excitation mechanism. Atomic data calculations for all configurations with n = 3 - 6 have been carried out and were employed in spectral modelling. Taking into account the proposed excitation channels, excellent overall agreement is found. Successful cross-checks with the spectral interval near the -line are demonstrated. The spectral modelling is proposed for sensitive density (electron density, excited state population) and temperature diagnostics near the target surface.

The first precision measurements of the wavelengths and identifications were made of the satellites of the Heb line of the Si XIII ion in the emission spectrum of a laser plasma. These satellites were the result of radiation decay of the 1s3l12l2 levels of the Si XII ion. The wavelengths were determined more accurately for the 1s3l13l2 configurations. The experimental results obtained were compared with calculations carried out by various methods. The structure of the relative intensities of the 1s3l13l2 satellites indicated that their emission occurred mainly in a thin overdense plasma region with Ne>Necr.

Spherically curved crystal spectrometers are demonstrated for use on an Electron Beam Ion Trap (EBIT) for the first time. Such spectrometers are characterized by high light collection efficiency and relative insensitivity to source position, simultaneously, giving them an advantage that no X-ray spectrometer previously used on an EBIT has had. One of the spectrometer crystals tested is composed of mica, giving it the additional advantage that it can be used with reasonable efficiency up to very high order, allowing spectra to span a broad wavelength range from 0.5 Angstroms to 20 Angstroms. Spectra from Ne-like barium and He-like argon are presented.

Essential parameters for the application of crystals to quantitative X-ray spectroscopy are the upper wavelength limit and the quantitative reflection properties (intrinsic resolving power, luminosity) of the crystal. Due to the large lattice constant, muscovite, a mica group mineral, can be used in the wavelength range up to about 2nm. Muscovite crystals can be bent to small radii of curvature due to their favourable cleavage and elastic properties. Characteristic reflection properties at reflections 002 – 00 24 were investigated theoretically and experimentally. The integrated reflectivity was calculated for various reflections of perfect flat as well as spherically bent muscovite crystals with curvature radii R = 100 and R = 186mm. It was measured for flat crystals in the reflections 00 10 – 00 26 using CuKα- and MoKα-radiation from X-ray tubes and compared with calculations for both perfect and mosaic crystals. Available high-quality muscovite crystals have a mosaic structure with a mosaic spread of about 1 arcmin. This mosaic spread limits the spectral resolving power for high reflection orders.

A new simple method to get soft X-ray micro-radiographs of biological material with a spatial resolution reaching 50 nm is described. A thin film of lithium fluoride (LiF) works as image detector, storing the micro-radiograph obtained exposing biological material to Extreme Ultra-Violet and soft X-ray radiations. Scanning near-field optical microscope (SNOM) is used to read the micro-radiograph at nanometric resolution up to λ/12, collecting the fluorescence ( λ=650 nm) excited by an Ar+ laser light ( λ=458 nm).

Observations were made of expansion, in a transverse quasisteady magnetic field (B ≈ 10 T), of a Teflon plasma generated by Nd laser radiation (λ = 1.06 μm, E ≈ 6 J, and τ ≈ 1ns). Time-integrated two-dimensional images of the plasma radiance were obtained in the spectrum of continuous and line x-ray radiation and spectroholiograms were recorded of 21P1—11S0 and 23P1—11S0 lines of the He-like F VIII ion. The plasma radiation was found to be anisotropic relative to the expansion axis and the dependence of the intensity on the distance from the target changed as a result of the influence of the transverse magnetic field on the plasma dynamics.

The first precision (with an error of 0.4–1.6 mA) measurements were made of the wavelengths of x-ray spectral lines emitted as a result of n=4 — n'=2 transitions in the Ne- and Na-like Kr XXVII and Kr XXVI ions. The spectra were recorded by means of a spectrograph with a spherically bent mica crystal, characterised by a spectral resolution λ/Δλ ≈ 5 × 103. The dispersion characteristic of this crystal was determined with the aid of reference lines, which were emitted by the He-like Ar XVII ion. The wavelengths of a series of dielectronic satellites of the resonance line of the Ar XVII ion were identified and measured. The results obtained were compared with calculated data.

The properties of a monochromatic x-ray backlighting system based on a spherically bent crystal were investigated. Simulations of spatial resolution for spherically bent crystals with different radius of curvature and for several wavelengths of incidence radiation were done using the ray-tracing method. Test experiments were carried out to demonstrate the high spatial resolution using the incoherent soft x-ray radiation produced by laser- and x-pinch plasmas. Both experimental and theoretical results show that a spatial resolution of at least 4 μm can be obtained in a field of view ranging from a few mm to cm. The narrow spectral band of the diffracted beam (Δλ/λ ~ 3 × 10−4), the high efficiency of the presented scheme and the possibility of significantly reducing the self radiation of the studied object make it one of the most promising backlighting systems. This scheme permits the essential reduction of requirements of the source of radiation and could be a less costly alternative to using x-ray lasers for such purposes.

A focusing spectrograph with a spherical crystal was used to obtain two-dimensional images of an expanding laser plasma which transmitted monochromatic x-ray radiation from a plasma source. Experiments characterised by a high spectral (λ/Δλ ~ 104) and spatial (Δr < 10 μm) resolution showed that the brightness of the shadow images depended on the x-ray absorption mechanism and on the parameters of the investigated plasma. The method is suitable, in principle, for determination of the plasma parameters.

An investigation was made of the interaction of a nanosecond laser pulse with a 'puff' gas target at gas densities sufficient for the formation of a critical-density plasma. The parameters of the laser plasma formed in the central interaction region and at its periphery were determined by x-ray spectroscopic methods. The formation of a plasma channel was observed and it was attributed to self-focusing of the laser radiation in the ionised gas.

We present a detailed analysis of the spectrum of satellite transitions to the n = 23 and n = 2–4 Ne-like yttrium resonance lines. Satellite lines from the double excited 2s22p53l3l', 2s22p53l4l', 2s2p63l3l' and 2s2p63l4l' levels of Na-like Y as well as from 2s22p53l3l'3l" and 2s2p63l3l'3l" levels of Mg-like Y were observed in spectra from a laser-produced plasma. The x-ray spectra were recorded with high spectral resolution λ/Δλ ≈ 3500–5000 in the wavelength region of the n = 2–3 Ne-like resonance lines and with λ/Δλ > 1000 in the region of the n = 2–4 Ne-like resonance lines. A total of more than 50 spectral features were identified, and their wavelengths were measured. A simple intensity model was developed, which agreed well with the measured spectra and assisted the line identification. The consistency of the model for different spectral regions demonstrates the potential of the Na-like and Mg-like satellite lines for diagnosing plasma conditions.

Various x-ray spectroscopic methods were used to investigate a plasma generated by the interaction of short-wavelength excimer laser radiation pulses (12 ns, 0.308 μm, 4×1012 W cm-2) with flat targets. A comparison of the profiles and intensities of a number of observed spectral lines of the H-like, He-like, and Li-like sodium, magnesium, and aluminium ions with the results of the reported calculations made it possible to determine the spatial distributions of the laser plasma parameters up to distances of ~0.4 mm from the target surface. These parameters were compared with the predictions of a simple theoretical model of the absorption of short-wavelength radiation in a plasma. This showed that the absorption of such radiation (with the intensities used in this investigation) involved inverse bremsstrahlung in regions with an electron density much lower than the critical value.

Aluminum wire X-pinch experiments performed at the Cornell University XP pulsed power generator show detailed high resolution spectra for satellite lines of Li-like, Be-like, B-like and C-like ions. These lines, which correspond to transitions originating from autoionizing levels, are observed in the direction of the anode with respect to the hot X-pinch cross point. The intensities of such satellites are much smaller or absent in the direction of the cathode. These transitions are caused by collisions of ions with energetic electrons (5-15 keV) which are created by inductance between the hot spot and the anode. A collisional-radiative model was constructed using a non-Maxwellian electron energy distribution consisting of a thermal Maxwellian part plus a Gaussian part to represent the high energy electron beam. The shapes of the observed satellite structures are consistent with the calculated spectrum for electron temperatures between 30-100 eV, and beam densities of about 10−7 times the plasma electron density.

A dense jet of a plasma consisting of multiply charged ions was generated in the interaction of a laser plasma with a strong external axial magnetic field. It is shown that using the high-luminosity x-ray spectroheliograph technique allows to measure plasma emission spectra with 2-dimensional spatial resolution even in the cases when these spectra have small intensities. The x-ray spectroscopy and interferometry methods are used to measure plasma parameter distributions. The dependencies of Ne(z) and Te(z) measured in this paper can be used to calculate the evolution of plasma ionization state during plasma expansion. The quasihomogeneous laser jet, which appears when a laser plasma interacts with an external magnetic field can be used not only to form an active medium of a short wavelength laser, but probably also to tackle the urgent problem of transport in a laser ion injector.

The emission spectra of a high-temperature recombining laser plasma and of an X-pinch plasma were used in high-precision (± 0.03–0.05 pm) measurements of the wavelengths of the Al XII lines resulting from the 1snp1P1—1s2 1S0 (n = 6–12) transitions. The lines due to transitions from the 1s11p and 1s12p levels of the He-like Al XII ion were observed for the first time. The experimental results were compared with calculations carried out by several theoretical methods.

New excitation channels for the explanation of the strong emission of Li-like and Be-like satellite transitions in numerous picosecond and subpicosecond laser-produced plasma experiments are proposed. `Blue Li-like satellites' of the He-like resonance line W are predicted. Corresponding spectral simulations exploiting new calculated atomic data for these mechanisms are in rather good agreement with experimental single-shot spectra of plasma produced at the intensities up to and recorded by means of a high-resolution spherically bent mica crystal technique.

X-ray spectroscopic methods were used to investigate the spatial distribution of Z-pinch plasma parameters. Experiments were carried out on the GAEL pulse line generator in Ecole Polytechnique (France) with different types of load. Obtained results for the concentration of electrons and plasma temperature showed that higher plasma homogeneity was obtained in experiments with complex load. Spectrograms demonstrate the stabilization effect of the Al-jet.

An experimental x-ray spectroscopic investigation was made of the stabilisation of a Z pinch with a composite load in the GAEL (225 kA, 50 ns) accelerator. Kinetic calculations of the intensities of the L lines in the spectrum of copper were used for the first time to determine the parameters of a plasma [Ne ? (1?2)?1020 cm-3, Te ? 300 keV] formed by injection of a cylindrical aluminium-plasma jet imploding onto an axial copper wire. Quantitative and qualitative analyses were made of the stabilisation of the Z pinch with a composite load. Spectroscopic methods were used to demonstrate the stabilising influence of the plasma jet. The results indicated that it should be possible to construct a homogeneous high-temperature plasma column.

We present X-ray spectroscopic diagnostics in femto-second laser-driven experiments revealing nonlinear phenomena caused by the strong coupling of the laser radiation with the created plasma. Among those nonlinear phenomena, we found the signatures of the Two Plasmon Decay (TPD) instability in a laser-driven CO_2 cluster-based plasma by analyzing the Langmuir dips in the profile of the O VIII Lyε line, caused by the Langmuir waves created at the high laser intensity 3x10^18 Wcm^-2. With similar laser intensities, we reveal also the nonlinear phenomenon of the Second Harmonic Generation (SHG) of the laser frequency by analyzing the nonlinear phenomenon of satellites of Lyman δ and ε lines of Ar XVII. In the case of relativistic laser-plasma interaction we discovered the Parametric Decay Instability (PDI)-induced ion acoustic turbulence produced simultaneously with Langmuir waves via irradiation of thin Si foils by laser intensities of 10^21 Wcm^-2.

We present X-ray spectroscopic diagnostics in femto-second laser-driven experiments revealing nonlinear phenomena caused by the strong coupling of the laser radiation with the created plasma. Among those nonlinear phenomena, we found the signatures of the Two Plasmon Decay (TPD) instability in a laser-driven CO2 cluster-based plasma by analyzing the Langmuir dips in the profile of the O VIII Lyϵ line, caused by the Langmuir waves created at the high laser intensity 3 1018Wcm-2. With similar laser intensities, we reveal also the nonlinear phenomenon of the Second Harmonic Generation (SHG) of the laser frequency by analyzing the nonlinear phenomenon of satellites of Lyman δ and ϵ lines of Ar XVII. In the case of relativistic laser-plasma interaction we discovered the Parametric Decay Instability (PDI)-induced ion acoustic turbulence produced simultaneously with Langmuir waves via irradiation of thin Si foils by laser intensities of 1021Wcm-2.

Mica crystals are widely applied in x-ray spectroscopy diagnostics since their ability to effectively reflect the radiation in different orders covering a wide range of photon energy, including sub-keV range hardly accessible with other crystals. Particularly, spherically bent mica crystals are commonly used in high energy density plasma imaging spectrometry diagnostics. However, the detailed reflectivity properties of bent mica crystals are not known well. Here we propose and verify the way to calibrate mica crystal spectral reflectivity in the experiment with relativistic laser plasma. The approach is based on the comparison of dense laser plasma x-ray spectra measured by focusing spectrometers with spatial resolution equipped, with examined mica and pre-calibrated alpha-quartz bent crystals. As a result, the normalized reflectivity of spherically bent mica crystal operated in 2nd order of reflection was experimentally evaluated for the first time versus wavelength in the range of 6.7-8.7 A. The obtained spectral calibration curve for bent mica crystal demonstrates remarkable difference to that one calculated for flat mica crystal and given in Henke tables and has to be applied further for a correct interpretation of the measured x-ray spectra.