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X-ray absorption spectroscopy is proposed as a method for studying the heating of solid-density matter excited by secondary X-ray radiation from a relativistic laser-produced plasma. The method was developed and applied to experiments involving thin silicon foils irradiated by 0.5–1.5 ps duration ultrahigh contrast laser pulses at intensities between 0.5 × 1020 and 2.5 × 1020 W∕cm2. The electron temperature of the material at the rear side of the target is estimated to be in the range of 140–300 eV. The diagnostic approach enables the study of warm dense matter states with low self-emissivity.

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.

We have discovered a new regime of bright coherent x-ray generation by relativistic plasma singularities driven by a multi-terawatt femtosecond laser focused onto a gas jet target [1]-[2]. The laser pulse propagates through the plasma, pushes electrons producing an electron-free cavity, and generates a bow wave [3]; singularities are produced at the joining of the cavity wall and the bow wave and represent point-like coherent x-ray emitters, which is a realization of Burst Intensification by Singularity Emitting Radiation (BISER) proposed in [4]. \nIn previous experiments, BISER occurred spontaneously, after the relativistic self-focusing, resulting in relatively large fluctuations of the x-ray source position and low overall stability. Based on simulations with the Particle-In-Cell (PIC) REMP code [5], we propose to control the BISER with a tailored plasma density profile. We demonstrate the BISER control employing a sharp plasma density jump generated by a shock in supersonic gas flow in experiments with the J-KAREN-P laser [6]-[7]. The induced BISER resulted in controllable x-ray source with low-jitter position and higher x-ray yield. Our results, on the one hand, represent an important step towards implementation of a next-generation bright compact coherent x-ray source, and on the other hand, demonstrate the new technique of relativistic self-focusing control and its diagnostics. \nWe thank the J-KAREN-P laser operation group and I. Daito for technical support. We acknowledge the financial support from JSPS Kakenhi JP 25390135 and JP 26707031. \n[1]A. S. Pirozhkov, et al., Phys. Rev. Lett. 108, 135004-5, (2012). [2]A. S. Pirozhkov et al., New J. Phys. 16, 093003-30 (2014). [3]T. Zh. Esirkepov, Y. Kato, and S. V. Bulanov, Phys. Rev. Lett. 101, 265001-4 (2008). [4]A. S. Pirozhkov, T. Zh. Esirkepov, et al., Scientific Reports 7, 17968 (2017). [5]T. Zh. Esirkepov, Comput. Phys. Comm. 135, 144-153 (2001). [6]H. Kiriyama, et al., IEEE J.S.T.Quantum Electron. 21, 1601118-18 (2015). [7]A. S. Pirozhkov, et al., Opt. Express 25, 20486-20501 (2017)., JPS Spring Meeting

We have discovered Burst Intensification by Singularity Emitting Radiation (BISER) [1], a new phenomenon which in particular results in bright coherent x-ray generation by relativistic plasma singularities driven by a multi-terawatt femtosecond laser focused onto a gas jet target [2], [3]. Singularities are produced in plasma by the laser pulse which pushes electrons creating an electron-free cavity and bow wave [4]. The singularities at the joining of the cavity wall and bow wave manifest themselves as point-like coherent x-ray emitters. A spontaneous BISER regime realized in previous experiments exhibits relatively large shot-to-shot fluctuations of the x-ray source position and low overall stability because the emission occurs after the relativistic self-focusing. However, stability is desirable for prospective applications of the new coherent x-ray source. \nA tailored plasma density profile can help to control the BISER, as shown by our simulations with the PIC REMP code [5]. Here, we present an experiment with the plasma profile tailoring, where a shock in supersonic gas flow generates a sharp density up-jump. We demonstrate the BISER control using this density jump scheme and the J-KAREN-P laser [6]-[7]. In contrast to the spontaneous regime, here we obtain low-jitter x-ray source position and higher x-ray yield. Moreover, these advantages are achieved simultaneously in an optimized case. Our results represent a crucial step towards implementation of the next-generation bright compact coherent x-ray source. Further, they demonstrate the new technique of relativistic self-focusing control and its diagnostics. \nWe thank the J-KAREN-P laser operation group. We acknowledge the financial support from JSPS Kakenhi JP 25390135 and JP 26707031. \n[1]A. S. Pirozhkov, T. Zh. Esirkepov, et al., "Burst intensification by singularity emitting radiation in multi-stream flows," Scientific Reports 7, 17968 (2017). [2]A.S.Pirozhkov, et al. "Soft-X-Ray Harmonic Comb from Relativistic Electron Spikes" Phys. Rev. Lett. 108, 135004 (2012). [3]A.S.Pirozhkov et al., "High order harmonics from relativistic electron spikes" New J. Phys. 16, 093003-30 (2014). [4]T. Zh. Esirkepov, Y. Kato, and S. V. Bulanov, "Bow Wave from Ultraintense Electromagnetic Pulses in Plasmas," Phys. Rev. Lett. 101, 265001-4 (2008). [5]T. Zh. Esirkepov, "Exact charge conservation scheme for Particle-in-Cell simulation with an arbitrary form-factor," Comput. Phys. Comm. 135, 144-153 (2001). [6]H. Kiriyama, et al., "High-Contrast, High-Intensity Petawatt-Class Laser and Applications," IEEE J.S.T.Quantum Electron. 21, 1601118-18 (2015). [7]A.S.Pirozhkov, et al. "Approaching the diffraction-limited, bandwidth-limited Petawatt" Opt. Express 25, 20486 (2017)., JSAP Spring Meeting

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.

The use of gas cluster media as a target for an intense femtosecond laser pulses is considered to be uniquely convenient approach for the development of a compact versatile pulsed source of ionizing radiation. Also, one may consider cluster media as a nanolab to investigate fundamental issues of intense optical fields interaction with sub-wavelength scale structures. However, conventional diagnostic methods fail to register highly charged ion states from a cluster plasma because of strong recombination in the ambient gas. In the paper we introduce high-resolution X-ray spectroscopy method allowing to study energy spectra of highly charged ions created in the area of most intense laser radiation. The emission of CO2 clusters were analyzed in experiments with 60 fs 780 nm laser pulses of 1018 W/cm2 intensity. Theory and according X-ray spectra modeling allows to reveal the energy spectra and yield of highly charged oxygen ions. It was found that while the laser of fundamental frequency creates commonly expected monotonic ion energy spectrum, frequency doubled laser radiation initiates energy spectra featuring of distinctive quasi-monoenergetic peaks. The later would provide definite advantage in further development of laser-plasma based compact ion accelerators.

The physics of compressible turbulence in high energy density (HED) plasmas is an unchartered experimental area. Simulations of compressible and radiative flows relevant for astrophysics rely mainly on subscale parameters. Therefore, we plan to perform turbulent hydrodynamics experiments in HED plasmas (TurboHEDP) in order to improve our understanding of such important phenomena for interest in both communities: laser plasma physics and astrophysics. We will focus on the physics of supernovae remnants which are complex structures subject to fluid instabilities such as the Rayleigh–Taylor and Kelvin–Helmholtz instabilities. The advent of megajoule laser facilities, like the National Ignition Facility and the Laser Megajoule, creates novel opportunities in laboratory astrophysics, as it provides unique platforms to study turbulent mixing flows in HED plasmas. Indeed, the physics requires accelerating targets over larger distances and longer time periods than previously achieved. In a preparatory phase, scaling from experiments at lower laser energies is used to guarantee the performance of future MJ experiments. This subscale experiments allow us to develop experimental skills and numerical tools in this new field of research, and are stepping stones to achieve our objectives on larger laser facilities. We review first in this paper recent advances in high energy density experiments devoted to laboratory astrophysics. Then we describe the necessary steps forward to commission an experimental platform devoted to turbulent hydrodynamics on a megajoule laser facility. Recent novel experimental results acquired on LULI2000, as well as supporting radiative hydrodynamics simulations, are presented. Together with the development of LiF detectors as transformative X-ray diagnostics, these preliminary results are promising on the way to achieve micrometric spatial resolution in turbulent HED physics experiments in the near future.

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.

1.Experimental discovery of new high-order harmonic generation regime \nWe discovered [1],[2] a new regime of bright high-order harmonic generation by multi-terawatt femtosecond lasers [3],[4] focused to micrometer spots in supersonic gas jets, Fig. 1(a). The focused laser irradiance exceeded 10^18 W/cm^2 rendering the interaction relativistically intense. Using either linearly or circularly polarized laser pulses, we observed coherent x-rays emitted from the gas jet. The obtained spectra were comb-like, with hundreds of even and odd harmonic orders reaching the 'water window', up to the photon energy of 360 eV. We found that the photon number scaled quadratically with the laser power. With a 120 TW laser, we obtained 4x10^9 photons (90 nJ pulse energy) in a single harmonic at 120 eV. Our experimental results were surprising and could not be explained by existing theories. \n2.Simulations and catastrophe theory model \nWe performed Particle-In-Cell (PIC) simulations and found that the harmonics were generated by extremely high-density, sharp electron density spikes; the peak density was orders of magnitude larger than the density of the unperturbed plasma. The emission was coherent due to the constructive interference of waves emitted by a strongly localized source. \nWe developed a model based on the catastrophe theory explaining the formation and robustness of the density spikes. The laser pulse pushed the electrons aside (away from the laser axis), creating an almost void cavity in the electron density and an outgoing bow wave [5]. The electrostatic potential of the remaining ions pulled background electrons transversely toward the laser axis. This created multi-stream plasma motion, which, in accordance with catastrophe theory, resulted in the formation of several types of density catastrophes (singularities). Sharp outlines of the cavity wall and bow wave corresponded to fold catastrophes. The density spike corresponded to a higher-order cusp catastrophe at the joint of two folds. Thus, the model predicted that the harmonics were generated by extremely localized, nanometer-scale sources. In particular, for linearly polarized lasers, the model predicted two singularities (point-like sources) situated in the laser polarization plane. Because of the small source size, the angular distribution of the x-ray emission was relatively broad, up to ~20-30°. \n3.Experimental confirmation of theory predictions: point-like double x-ray source and off-axis harmonics \nWe performed dedicated experiments and confirmed these cornerstone theory predictions. In particular, we detected coherent off-axis XUV radiation [6] and recorded bright soft x-ray harmonics within the off-axis observation angle range from 8 to 18° [7]. Employing a high-resolution LiF detector [6], we imaged the emitters and obtained two point-like sources situated along the laser polarization direction [7]. The direct observation gave a 0.8 um source size, which was limited by geometrical aberrations of the spherical mirror. The presence of fine fringes indicated that the actual source size was much smaller, of the order of 100 nm or less. \n4.Challenges for imaging x-ray optics \nIt is extremely important to measure the source size with higher resolution, as the simulations predict that the source can be as small as ~10 nm. Together with wide angular distribution, this represents a great challenge for imaging x-ray optics. Additional difficulty comes from the multi-TW laser, which must be filtered out. We are now preparing experiments with high-resolution normal-incidence imaging multilayer mirrors [8]; another option could be a variation of the coherent diffractive imaging. \n5.Ultrabright compact coherent x-ray source \nOur findings open a way to a new ultra-bright, spatially and temporally coherent x-ray source driven by a compact high-power laser, available for university- and industry labs. The photon energy can reach a few keV with petawatt driving lasers. Moreover, the peak spectral brightness of the new source can approach the record held by free-electron lasers in the photon energy range from 10 eV to ~ 1 keV. \n[1]A. S. Pirozhkov, M. Kando, T. Zh. Esirkepov, P. Gallegos, H. Ahmed, E. N. Ragozin, A. Y. Faenov, T. A. Pikuz, et al., "Soft-X-Ray Harmonic Comb from Relativistic Electron Spikes," Phys. Rev. Lett. 108, 135004-5 (2012). \n[2]A. S. Pirozhkov, M. Kando, T. Zh. Esirkepov, P. Gallegos, H. Ahmed, E. N. Ragozin, A. Y. Faenov, T. A. Pikuz, T. Kawachi, et al. "High order harmonics from relativistic electron spikes" New J. Phys. 16, 093003-30 (2014). \n[3]H. Kiriyama, M. Mori, Y. Nakai, T. Shimomura, M. Tanoue, et al., "High-contrast, high-intensity laser pulse generation using a nonlinear preamplifier in a Ti : sapphire laser system", Opt. Lett. 33, 645-647 (2008). \n[4]C. J. Hooker, J. L. Collier, O. Chekhlov, R. Clarke, E. Divall, K. Ertel, B. Fell, P. Foster, et al., "The Astra Gemini project -- A dual-beam petawatt Ti:Sapphire laser system", J. Phys. IV France 133, 673-677 (2006). \n[5]T.Esirkepov, Y.Kato, S.Bulanov, "Bow Wave from Ultraintense Electromagnetic Pulses in Plasmas" PRL 101 265001 (2008). \n[6]T. Pikuz, A. Faenov, A. Pirozhkov, A. Astapov, G. Klushin, S. Pikuz, et al., "High performance imaging of relativistic soft X-ray harmonics by sub-micron resolution LiF film detectors," Physica Status Solidi C 9, 2331 (2012). \n[7]A. S. Pirozhkov, T. Zh. Esirkepov, T. A. Pikuz, A. Ya. Faenov, K. Ogura, Y. Hayashi, H. Kotaki, E. N. Ragozin, et al., "Burst intensification by singularity emitting radiation in multi-stream flows," arXiv:1611.05547 (2016). \n[8]A.S.Pirozhkov, E.N.Ragozin "Aperiodic multilayer structures in soft X-ray optics" Phys. Usp. 58 1095 (2015)., The 14th Symposium on X-ray Imaging Optics

The behaviour of high power laser driven ion generation at the extreme intensities available at state-of-the-art and next-generation laser facilities is an important topic for realising potential applications. One of the simplest schemes for proton sources for applications is sheath acceleration, for which different established models predict varying dependence on laser and target parameters, motivating experimental investigation. We will present experimental data investigating sheath driven proton acceleration using the ultra-high intensity, high contrast J-KAREN-P laser. A ~10 J, 40 fs pulse was focused to an intensity ~5x1021 Wcm-2, generating protons up to 50 MeV from freestanding ~μm foils, and up to 40 MeV at 0.1 Hz from a 5 μm tape target, with conversion efficiencies >1% into protons above 10 MeV. Scaling with different methods of laser intensity variation will be discussed. Simultaneous measurement of the electron distribution and optical probing of plasma formation on the rear target surface provide insights into electron absorption. In particular, target irradiation at 45º angle of incidence is shown to produce a systematic asymmetry in both rear surface sheath formation and resultant proton distribution due to the initial non-thermal electron distribution, causing the highest energy protons to be steered partly towards the laser axis., EAAC2017参加

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.

The dynamic fracture of tantalum is observed at the atomic scale using an x-ray monitoring technique at the SACLA XFEL facility., The understanding of fracture phenomena of a material at extremely high strain rates is a key issue for a wide variety of scientific research ranging from applied science and technological developments to fundamental science such as laser-matter interaction and geology. Despite its interest, its study relies on a fine multiscale description, in between the atomic scale and macroscopic processes, so far only achievable by large-scale atomic simulations. Direct ultrafast real-time monitoring of dynamic fracture (spallation) at the atomic lattice scale with picosecond time resolution was beyond the reach of experimental techniques. We show that the coupling between a high-power optical laser pump pulse and a femtosecond x-ray probe pulse generated by an x-ray free electron laser allows detection of the lattice dynamics in a tantalum foil at an ultrahigh strain rate of ε. ~2 × 108 to 3.5 × 108 s−1. A maximal density drop of 8 to 10%, associated with the onset of spallation at a spall strength of ~17 GPa, was directly measured using x-ray diffraction. The experimental results of density evolution agree well with large-scale atomistic simulations of shock wave propagation and fracture of the sample. Our experimental technique opens a new pathway to the investigation of ultrahigh strain-rate phenomena in materials at the atomic scale, including high-speed crack dynamics and stress-induced solid-solid phase transitions.

We report on the J-KAREN-P laser facility at QST, which can provide PW peak power at 0.1 Hz on target. The system can deliver short pulses with an energy of 30 J and pulse duration of 30 fs after compression with a contrast level of better than 1012. Such performance in high field science will give rise to the birth of new applications and breakthroughs, which include relativistic particle acceleration, bright x-ray source generation, and nuclear activation. The current achieved laser intensity on target is up to > 9x1021 Wcm-2 with an energy of ~9 J on target. The interaction with a 3 to 5- μm stainless steel tape target provides us electrons with a typical temperature of more than 10 MeV and energetic proton beams with typical maximum energies of > 40 MeV with good reproducibility. The protons are accelerated in the Target Normal Sheath Acceleration regime, which is suitable for many applications including as an injector into a beamline for medical use, which is one of our objectives.

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.

In our experiments and simulations [1, 2] we discovered a bright source of high-order harmonics and revealed the mechanism of their generation in relativistic plasma driven by multi-terawatt femtosecond lasers focused onto gas jet targets with typical electron densities of ~10^19 cm^-3. The harmonics extended up to the 'water window'; the energy within the 60 to 100 eV bandwidth was up to 100 nJ per shot. Simulations showed that the emission consisted of several attosecond pulses. In our subsequent experiments we confirmed the predictions and observed the soft x-ray emission originated from point-like sources. \nHere we generalize this mechanism and introduce the concept of BISER, Burst Intensification by Singularity Emitting Radiation. In this concept, we consider an emitting medium with multi-stream flows. Elementary components participating in such flows eventually form structurally stable density singularities explained by catastrophe theory. The wave emission from such singularities can be coherent due to tight localization of elementary emitters. In addition, if the singularities move with relativistic speed towards an observer, the apparent frequency increases and emission becomes more intense and directional. In our previous work the emitting medium was relativistic plasma, the elementary components were electrons, and the emitting waves were high-frequency electromagnetic waves, i.e. soft x-rays. In general, BISER can be applicable to any type of traveling waves, not necessarily electromagnetic. \n[1] A. S. Pirozhkov, M. Kando, T. Zh. Esirkepov, et al., "Soft-X-Ray Harmonic Comb from Relativistic Electron Spikes," Phys. Rev. Lett. 108, 135004-5 (2012). [2] A. S. Pirozhkov, M. Kando, T. Zh. Esirkepov, et al., "High order harmonics from relativistic electron spikes," New J. Phys. 16, 093003-30 (2014)., The Optics & Photonics International Congress OPIC-2017, International Conference on High-Energy Density Sciences HEDS-2017

Acceleration of particles from the interaction of ultra-intense laser pulses up to $5\times10^{21}$ Wcm$^{-2}$ 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 focii has reducing returns for some applications.

The short review on the possible applications of the hollow ion spectra for the diagnostics of the high-temperature plasma created by intensive laser and particle beams is presented. Because of the hollow ion spectra features are defined mainly by the mechanisms of their excitation, we consider the various types of the high-temperature plasma where different excitation processes are important. It is shown that like ordinary spectral lines, spectra of the hollow ions offer considerable diagnostic opportunities. At the present time, hollow ion spectra are used mainly to investigate plasma heated by X-ray radiation, but the hollow ions must be generated when plasma is heated by fast heavy ion beams too. In this case, the resultant substance state will be also characterized by solid-state density, and some spatial regions of targets will have relatively low temperatures, i.e., will be a nonideal plasma. It is emphasized that hollow ion spectra are promising diagnostic tool for both nonideal plasma and warm dense matter.

The possibility is discussed of using optical laser radiation with an intensity of W cm to create an ultraintense X-ray source capable of producing polychromatic radiation with a power flux of W cm or higher. X-ray radiation of so high an intensity permits not only transforming a condensed matter of the target into a plasma state but also obtaining an exotic plasma state with a high density of hollow ions. Currently not yet in wide use and available in only a few laboratories in the world, lasers with a radiation intensity of about W cm are more compact and less expensive than free-electron X-ray lasers or lasers used for the indirect heating of fusion targets. The source under discussion can produce by far higher X-ray intensities than plasma X-ray lasers of a similar scale.

An inhomogeneous spatial distribution of laser accelerated carbon/oxygen ions produced via the hydrodynamic ambipolar expansion of CO_2 clusters has been measured by using CR-39 detectors. An inhomogeneous etch pits spatial distribution has appeared on the etched CR-39 detector installed on the laser propagation direction, while homogeneous ones are appeared on those installed at 45 and 90 from the laser propagation direction. From the range of ions in CR-39 obtained by using the multi-step etching technique, the averaged energies of carbon/oxygen ions for all directions are determined as 0.78 ± 0.09 MeV/n. The number of ions in the laser propagation direction is about 1.5 times larger than those in other directions. The inhomogeneous etch pits spatial distribution in the laser propagation direction could originate from an ion beam collimation and modulation by the effect of electromagnetic structures created in the laser plasma.

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.

High-order harmonics from relativistic singularities are emitted when a multi-terawatt femtosecond laser irradiates a gas jet target [1, 2]. The laser pulse pushes electrons producing an electron-free cavity and generates a bow wave [3]; the singularities are produced at the joining of the cavity wall and the bow wave and represent point-like coherent x-ray emitters. The emitted spectra generally consist of high-order harmonics of optical frequency. However, the spectra often exhibit additional features such as modulations with large period (up to 10s of eV) and presence of several periods in a single spectrum. Here we report on analysis of experimental spectra with the emphasis on dependence on laser and plasma parameters, and discuss possible implications. This work was supported by JSPS KAKENHI # JP 25287103, JP 25390135, and JP 26707031., JPS Spring Annual Meeting

We report on discovery of bright XUV and soft x-ray sources emitting coherent radiation due to formation of relativistic plasma singularities., International Symposium "Nanophysics and Nanoelectronics”

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 ~10^21 W/cm^2). 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.

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.

Understanding the physics of laser-matter interactions in ultrashort pulses is important for many well-acknowledged applications from material modifications to biology. We numerically and experimentally consider the effect of sub-picosecond Ti:sapp laser actions on 60-100 nm gold films mounted onto a fused silica substrate. The pulse energy is sufficient to ablate the films. For the first time, we show that there are different regimes of ablation, and the formation of the 3D structures depends on the value of the absorbed fluence Fabs and the adhesion strength padh between the film and the substrate. Namely, a delamination threshold Fdelam and an ablation threshold Fabl (Fdelam < Fabl) exist if adhesion is weak. Above the lower threshold Fdelam, the whole film delaminates from the substrate. Above the higher threshold Fabl, the thin film ruptures near its middle plane. The external half of the film flies away, while the internal half remains on the glass substrate. There are two thresholds Fdelam and Fabl...