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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 for the Au/glass and Ag/glass targets, because pure gold and silver are weakly coupled to the glass. The lower threshold Fdelam disappears in the case of a strong adhesion stress padh. Consequently, delamination as a whole becomes impossible. Although the rupture of a film remains because the ablation threshold Fabl is independent of on adhesion. Adhesion is high when an intermediate thin layer of chromium is placed between the gold and the glass. The film velocity after it separates from the substrate is low for the range of fluences Fdelam < F < Fabl because the acoustic impedance Zglass of glass is small relative to the impedance Zfilm of a gold film. Therefore, during an evolution, the absolute values (positive or negative) of the contact pressures are few times smaller than the absolute pressures in a gold film. However, above the ablation threshold Fabl < F, the velocity of the external part of a film becomes few times larger because the velocity is independent of the acoustic impedance of a substrate. These circumstances explain why 3D structures such as nanojet above the microbump appears in the case of a weak adhesion. The velocity should be not too large to allow to the surface tension and crystallization to stop an inflation and breakaway of a microbump. [ABSTRACT FROM AUTHOR]

We propose a new mechanism of high-order harmonic generation during an interaction of a high-intensity laser pulse with underdense plasma. A tightly focused laser pulse creates a cavity in plasma pushing electrons aside and exciting the wake wave and the bow wave. At the joint of the cavity wall and the bow wave boundary, an annular spike of electron density is formed. This spike surrounds the cavity and moves together with the laser pulse. Collective motion of electrons in the spike driven by the laser field generates high-order harmonics. A strong localization of the electron spike, its robustness to oscillations imposed by the laser field and, consequently, its ability to produce high-order harmonics is explained by catastrophe theory. The proposed mechanism explains the experimental observations of high-order harmonics with the 9 TW J-KAREN laser (JAEA, Japan) and the 120 TW Astra Gemini laser (CLF RAL, UK) [A. S. Pirozhkov, et al., arXiv:1004.4514 (2010); A. S. Pirozhkov et al, AIP Proceedings, this volume]. The theory is corroborated by high-resolution two-and three-dimensional particle-in-cell simulations. [ABSTRACT FROM AUTHOR]

We report on novel methods to generate ultra-short, coherent, X-rays using a laserplasma interaction. Nonlinear interaction of intense laser pulses with plasma creates stable, specific structures such as electron cusps. For example, wake waves excited in an underdense plasma by an intense, short-pulse laser become dense and propagate along with the laser pulse. This is called a relativistic flying mirror. The flying mirror can reflect a counter-propagating laser pulse and directly convert it into high-frequency radiation, with a frequency multiplication factor of ∼ 4γ2 and pulse shortening with the same factor. After the proof-of-principle experiments, we observed that the photon number generated in the flying mirror is close to the theoretical estimate. We present the details of the experiment in which a 9 TW laser pulse focused into a He gas jet generated the Flying Mirror, which partly reflected a 1 TW pulse, giving up to ∼ 1010 photons, 60 nJ (1.4×1012 photons/sr) in the XUV spectral region (12.8-22 nm). [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a new regime of high-order harmonic generation by relativistic-irradiance lasers in gas jet targets. Bright harmonics with both odd and even orders, generated by linearly as well as circularly polarized pulses, are emitted in the forward direction, while the base harmonic frequency is downshifted. A 9 TW laser generates harmonics up to 360 eV, within the 'water window' spectral region. With a 120 TW laser producing 40 uJ/sr per harmonic at 120 eV, we demonstrate the photon number scalability. The observed harmonics cannot be explained by previously suggested scenarios. A novel high-order harmonics generation mechanism [T. Zh. Esirkepov et al., AIP Proceedings, this volume], which explains our experimental findings, is based on the phenomena inherent in the relativistic laser - underdense plasma interactions (self-focusing, cavity evacuation, and bow wave generation), mathematical catastrophe theory which explains formation of electron density singularities (cusps), and collective radiation due to nonlinear oscillations of a compact charge. [ABSTRACT FROM AUTHOR]

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

Generation of high energy negative ions by laser-plasma interaction is studied theoretically and numerically. New acceleration process called Coulomb implosion mechanism is proposed, which explains efficient acceleration of negative ions from laser-plasmas. The model is confirmed by using 2-dimenstional Particle-in-Cell simulations. Experimental evidence of negative ion acceleration from cluster target is also presented. [ABSTRACT FROM AUTHOR]

The intense isotropic source of multicharged ions, with energy above 300 keV, was produced by femtosecond Ti:Sa laser pulses irradiation (intensity of ∼4×1017 W/cm2) of the He and CO2 gases mixture expanded in supersonic jet. High contrast ionography images have been obtained for 2000 dpi metal mesh, 1 μm polypropylene and 100 nm Zr foils, as well as for different biological objects. Images were recorded on 1 mm thick CR-39 ion detector placed in contact with back surface of the imaged samples, at the distances 140–160 mm from the plasma source. The obtained spatial resolution of the image was ∼600 nm. A 100 nm object thickness difference was resolved very well for both Zr and polymer foils. The multicharged ion energy for Carbon and Oxygen ions passing through the 1 μm polypropylene foil is estimated to give the energy of more than 300 keV. An almost equal number of ions were measured with total number of about 108 per shot at a different direction from plasma source. Easy production of different sub-MeV ions in wide space angle, recognizes femtosecond-laser-driven-cluster-based plasma as a well-suited bright source for novel type of submicron ionography to image different media, including nanofoils, membranes, and other low-contrast objects. [ABSTRACT FROM AUTHOR]

The high-intensive source of soft X-ray emission was developed by femtosecond laser pulses irradiation of submicron size CO2 clusters, produced in custom designed super-sonic nozzle while mixing the 10% CO2+90% He expanding gases. The LiF crystal soft X-ray detectors have been used for obtaining absorption images of ultrathin (nanoscale) foils and biological structures illuminated by the developed source. It was demonstrated that even if the foil is essentially transparent for the soft X-ray radiation (like 100 nm thick Zr foil), the image contrast could be significantly increased due to the influence of propagation-based phase-contrast effect, by placing the detector at the proper distance from the sample. [ABSTRACT FROM AUTHOR]

We demonstrate generation of 10–20 MeV/u ions with a compact 4 TW laser using a gas target mixed with submicron clusters, corresponding to tenfold increase in the ion energies compared to previous experiments with solid targets. It is inferred that the high energy ions are generated due to formation of a strong dipole vortex structure. The demonstrated method has a potential to construct compact and high repetition rate ion sources for hadron therapy and other applications. [ABSTRACT FROM AUTHOR]

The excitation of X-ray plasma satellites was investigated in the plasma created by subpicosecond laser pulses with various intensities. It is shown that when laser flux density is greater then 6×1016 W/cm2 strong oscillating electrical fields with ω∼(1.5–1.6)×1015 s-1 are excited in the plasma. These oscillations lead to modifications of profiles of X-Ray spectral lines observed. [ABSTRACT FROM AUTHOR]

Dedicated laboratory astrophysics experiments have been developed at LULI in the last few years. First, a high velocity (70 km/s) radiative shock has been generated in a xenon filled gas cell. We observed a clear radiative precursor, measure the shock temperature time evolution in the xenon. Results show the importance of 2D radiative losses. Second, we developed specific targets designs in order to generate high Mach number plasma jets. The two schemes tested are presented and discussed. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The results of measurements of the multicharged ions spectra in plasma produced by moderately intense (up to 4×1017 W/cm-2) laser pulses are presented. In the first case, Nd glass laser radiation with energy 1 – 2 J and pulse duration 1.5 ps was focused on the flat solid Teflon target. In the second case, Ti:Sa laser radiation with energy ∼70 mJ and pulse duration 70 and 500 fs was focused onto an N2O gas jet, created by a high-pressure liquid nitrogen cooled, pulsed (10 Hz) nozzle. Profiles of the Lyα lines of F IX ions in Teflon target and O VIII ions in N2O clusters were recorded with a very high spectral resolution λ/δλ ∼ 3000 – 5000. The features (peaks and dips) in the Lyα line profiles were observed. They suggest the existence of intense plasma oscillations with a frequency appreciably lower than the frequency of the laser radiation. The observed X-ray spectra for the plasma satellites of the Lyα doublet of the hydrogen F IX and O VIII ions in plasma were modeled theoretically. It was shown that the resulting doublet profile have a complex structure, which depends nontrivially both on the plasma temperature, density and on the frequency and amplitude of the plasma oscillations. Experimental positions of the satellites and their separations allowed them to be associated with intense electrostatic oscillations with an amplitude E0 ∼ (4–6)×108 Vcm-1 and a frequency ω ∼ (0.7–1)×1015 s-1 for F IX ions and E0 ∼ (0.5 – 1.0)×10 9 V/cm and frequency ω ∼ (0.7–2.4)×1015 s-1 for O VIII, simultaneously. Assuming the oscillation frequency to be determined by the strength of the magnetic field B generated in the plasma, we obtained an estimate of B that is in reasonable agreement with other measurements. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The review of systematic investigations of X-ray radiation properties of different clusters heated by short-pulse (35-1100 fs) high-intensive (10[sup 16] - 10[sup 18] W/cm²) Ti:Sa laser radiation is presented. The cluster targets were formed by the adiabatic expansion in vacuum of an Kr or Ar gas jets produced by a pulsed valve with Laval or conical nozzles. The gas pressure is varied from 15 up to 100 bar. High spectrally (λ/δλ=4000-5000) and spatially (40-80 ·m) resolved X-Ray spectra near resonance lines (4-2 transitions) of Ne-like ions of Kr, H- and He-like ions of Ar have been obtained and detailed spectroscopic analysis was consistent with a theoretical two-temperature collisional-radiative model of irradiated atomic clusters incorporating with an effects of highly energetic electrons. The role of laser prepulse for X-ray intensity emission investigated in details. X-ray spectra radiation from plasma with electron density more than 2×10[sup 22] cm[sup -3] was observed. Big effect of fast electrons influence on the X-ray emission of He-like Ar and Ne-like Kr spectra was demonstrated. Comparison of data obtained under various experimental conditions clearly showed that for increasing X-ray output from plasma the most essential to increase size of clusters and has reasonable value of ps prepulse. [ABSTRACT FROM AUTHOR]

Dense plasmas have been created at the GSI with the one hundred joules nhelix-laser under well-defined hydrodynamics conditions. The application of two-dimensional x-ray optics enabled the registration of the Li-like satellite series ls21nl'-1s²21" with simultaneous high spectral and spatial resolution with excellent signal to noise ratio. The data show their emission is confined to the area of the laser spot thereby providing a localized emission source of the highest density region. The satellite transitions are also shown to be optically thin. Therefore, outstanding properties for Stark broadening analysis are met. The fast computer code PPP is capable to synthesise line shapes for experiment interpretation in a wide range of emitters and plasma conditions. Full Stark broadening calculations carried out with the PPP code involving the configurations 1s21nl' with n=2-7 demonstrate their advantageous properties. [ABSTRACT FROM AUTHOR]

We report new results using the LLNL COMET laser to evaluate the effectiveness of different target architectures to improve the output and characteristics ofthe transient x-ray laser scheme. Surprising observations were found when the laser line focus irradiating a single slab Cr or Fe target was divided into two or three distinct plasma column sections with millimeter scale gaps between each plasma. The Ne-like 3p [SUP1]S[SUB0] → 3s [SUP1]P[SUB1] 28.5 nm and 25.5 nm x-ray laser lines, for Cr and Fe, respectively, were improved in beam divergence, by 2 - 3 times, and peak intensity, by up to one order of magnitude, when compared with a single plasma column of the same length or longer. This was contrary to expectations since these large-scale inhomogeneities introduced along the plasma, as well as attenuation from the cold plasma at the end of each section, would be detrimental to the x-ray propagation and amplification. Instead an injectoramplifier (IA) type process appears to be at work where the plasma gaps may be beneficially modifying the ray propagation and coupling through the high Ne-like ion gain regions. We present results showing the output of the amplifier stage with increasing length for the IA targets together with beam deflection and divergence measurements. [ABSTRACT FROM AUTHOR]

In this paper, we report on the realization of a capillary discharge soft x-ray laser operating ar 46.9 nm pumped by a 30 kA peak value, 150 ns hall cycle duration current pulse (corresponding to a mean current slope of about 5 10[SUP11] A/s). The slope of the pumping current is sufficiently high to produce the plasma compression and laser amplification on the 3p-3s, J=0-1 transition of Ne-like Ar, in 2.4-4 mm in diameter alumina capillary channels. We have analyzed the output pulse characteristics of the produced laser beam, such as the lasing time and the pulse duration, the saturation and the output pulse energy, the near field image as a function of different experimental parameters. Using the same current pulse, the lasing effect has not been observed in polyacetal capillaries, demonstrating the damning role of the wall capillary ablation in the heating and in the stability of the plasma colunm during the z-pinch compression. [ABSTRACT FROM AUTHOR]

Recent progress in the novel information technologies based on the World-Wide Web (WWW) gives a new possibility for a worldwide exchange of atomic spectral and collisional data. This facilitates joint efforts of the international scientific community in basic and applied research, promising technological developments, and university education programs. Special-purpose atomic databases (ADBs) are needed for an effective employment of large-scale datasets. The ADB SPECTR developed at MISDC of VNIIFTRI has been used during the last decade in several laboratories in the world, including RFNC-VNIITF. The DB SPECTR accumulates a considerable amount of atomic data (about 500,000 records). These data were extracted from publications on experimental and theoretical studies in atomic physics, astrophysics, and plasma spectroscopy during the last few decades. The information for atoms and ions comprises the ionization potentials, the energy levels, the wavelengths and transition probabilities, and, to a lesser extent, — also the autoionization rates, and the electron-ion collision cross-sections and rates. The data are supplied with source references and comments elucidating the details of computations or measurements. Our goal is to create an interactive WWW information resource based on the extended and updated Weboriented database version SPECTR-W³ and its further integration into the family of specialized atomic databases on the Internet. The version will incorporate novel experimental and theoretical data. An appropriate revision of the previously accumulated data will be performed from the viewpoint of their consistency to the current state-of-the-art. We are particularly interested in cooperation for storing the atomic collision data. Presently, a software shell with the up-to-date Web-interface is being developed to work with the SPECTR-W³ database. The shell would include the subsystems of information retrieval, input, update, and output in/from... [ABSTRACT FROM AUTHOR]

The systematic experimental studies of plasma produced upon the interaction of ultrashort laser pulses with cluster targets are carried out using the methods of x-ray spectroscopy. The dependence of the plasma parameters on the initial properties of a cluster target such as the design of a supersonic nozzle, the average size of clusters, and their spatial distribution as well as the laser-pulse properties of duration and contrast are studied. The plasma diagnostics is performed using the model of spectra formation that provides a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Dense non-Maxwellian plasmas have been created at the high energy nhelix-laser test bed facility under well defined hydrodynamic conditions. Space resolved hot electron induced K[sub α]-emission from the target surface has been observed simultaneously with the x-ray radiation emission of highly charged target ions. Two-electron inner-shell transitions are introduced as reference lines to provide a unique parameter determination. Non-Maxwellian non-LTE kinetics simulations for opaque plasmas as well as Stark broadening calculations of complex autoionizing levels provide a proof of the proposed methods. Excellent agreements with the data are demonstrated. Space resolved x-ray Doppler spectroscopy provides fast ion energy distribution. [ABSTRACT FROM AUTHOR]