We have developed a new opacity modeling of partially ionized high-Z plasma to solve radiation transport in fluid codes. The average atom model is used to describe the electronic state of the plasma. The electronic state of the plasma is determined by solving the collisional radiative equilibrium model. We have taken into account the electron energy level splitting owing to the difference in the azimuthal quantum number. To model the line groups made of the same electronic transitions from ions indifferent charge states, we used a statistical method and calculated the distribution of the charge states from the averaged electron population in each bound state. By using the new opacity model, we can well reproduce the X-ray spectra from the plasmas. It is found that the Δn = 0 transition can explain the peaked spectra near hv = 300 eV and l–splitted emission of the n = 5–4 transition can explain the flat spectra in the region of hv = 400–800 eV seen in the experiments.

A program is under way to develop methods and instrumentation based on charge-coupled device (CCD) sensors for hot plasma diagnostics. We have developed a new X-ray spectrometer in which a freestanding X-ray transmission grating is coupled to a CCD linear array detector with electronic digitized readout replacing film and its wet processing. This instrument measures time-integrated pulsed X-ray spectra with moderate spectral resolution (δλ ≤ 0.6 nm) over a broad spectral range (0.3–2 keV) with high sensitivity, linearity, and large dynamic range. The performance of the device was tested using laser plasma as the X-ray source.

Electron injection into a laser wakefield by the colliding of two circularly polarized laser pulses is analyzed by the Hamiltonian approach and particle-in-cell simulations. If the pump pulse driving the laser wakefield is right-circularly-polarized, electron injection is found only when the counter-propagating injection pulse is left-circularly-polarized and vice versa. This holds when the injection pulse is at low intensity and has a frequency near the pump pulse frequency ω0. For a moderately intense injection pulse, even if the two pulses have the same polarization, electron injection is found but with less efficiency. It is also found that the injection pulse with the frequency within [0.5ω0,3ω0] can still create electron injection efficiently provided it has the opposite polarization with the pump pulse.

This paper gives the results of the investigations of four types of apodized (soft) apertures for beam shaping of UV, visible and IR high-power lasers with near-Gaussian and flat-top transmittance. The apodized apertures (AA) are ≈3–45 mm in diameter, but the principles of fabrication of such apertures lends the possibility of apodizing beams with diameter <1 mm and >200 mm. The examples of studies of the AA in high-power lasers are presented. The possibility of avoiding the Fresnel diffraction ripples is proved experimentally.

Laser induced ablation pressure as a function of absorbed laser intensity for low and moderate atomic number targets has been experimentally determined using a 1·06-μm laser at an irradiance of 5 × 1011 to 1 × 1013 W cm−2. Ablation pressure variations with the absorbed laser intensity indicate a transition from a self-regulating ablation to a deflagration scaling for low atomic targets. The experimental results have also been corroborated with theoretical models and a two dimensional hydrodynamic code.

The X-ray emission from an ultrashort-pulse laser incident on a solid aluminum and a layered aluminum /silicon slab is investigated with a non-LTE radiation-hydrodynamics model coupled to a Helmholtz wave equation for P-wave polarization. A fraction of the absorbed energy is expended in the production of fast electrons, which are transported and deposited in the cold material. These electrons create K-shell vacancies that produce characteristic Kα line radiation. A time history of the emission spectra, including the Kα lines and continuum radiation, is presented for a laser intensity of 1017 W/cm2.

In this paper, the possibility of using neural networks for fast tomographic reconstructions of tokamak plasma soft X-ray (SXR) emissivity is investigated. Indeed, the radiative cooling of heavy impurities like tungsten could be detrimental for the plasma core performances of ITER, thus developing robust and fast SXR diagnostic tools is a crucial issue to monitor the impurities and to mitigate in real-time their central accumulation. As preliminary work, a database of emissivity phantoms with associated synthetic measurements is used to train the neural network to solve the inversion problem. The inversion method, training process, and first tomographic reconstructions are presented with the perspectives about our future work.

We continue our previous investigations (Yang, Zabusky, & Chern, 1990; Zabusky & Zhang, 2002) of the interaction of a shock with a planar, inclined curtain (slow/fast/slow) to a wider Mach number range (M = 1.5, 2.0, and 5.0) and longer times. In all cases, the generic features may be explained in terms of the opposite-signed vortex layers (deposited by the shock wave), which approach and collide to form a complex vortex bilayer (VBL). At M ≤ 2.0, the VBL traverses the shock tube and eventually collides with the opposite horizontal boundary and evolves into upstream and downstream moving inhomogeneous vortex projectiles (VPs) (Zabusky & Zeng, 1998). This is manifested as early-time “breakthrough” (Yang, Zabusky, & Chern, 1990). During the traversal, we observe and scale a strong secondary baroclinic circulation enhancement. We track and quantify the VPs and show that their velocities compare well to that from a simple vortex model. We also display turbulent domains and a new rapid early time turbulization at M = 5, when the VBL is narrower.

The high energy loss of heavy ions in matter as well as the small angular scattering makes heavy ion beams an excellent tool to produce almost cylindrical and homogeneously excited volumes in matter. This aspect can be used to pump short wavelength lasers. For the first time, a beam of heavy ions was used to pump a short wavelength gas laser in an experiment performed at the GSI ion accelerator facility in December 2005. In this experiment, the well-known KrF* excimer laser was pumped with an intense uranium beam. Pulses of an uranium beam compressed down to 110 ns (full width at half maximum) with initial particle energy of 250 MeV per nucleon were stopped inside a gas laser cell. A mixture of an excimer laser premix gas (95.5%Kr + 0.5%F2) and a buffer gas (Ar) in different proportions was used as the laser gas. The maximum beam intensity reached in the experiment was 2.5 × 109 particles per pulse, which resulted in 34 J/g specific energy deposited in the laser gas. The laser effect on the transition at λ = 248 nm has been successfully demonstrated by various independent methods. There, the laser threshold was reached with a beam intensity of 1.2 × 109 particles per pulse, and the energy of the laser pulse of about 2 mJ was measured for an ion beam intensity of 2 × 109 particles per pulse. As a next step, it is planned to reduce the laser wavelength down to the vacuum ultraviolet spectral region, and to proceed to the excimer lasers of the pure rare gases. The perspectives for such experiments are discussed and the detailed estimations for Xe and Kr cases are given. We believe that the use of heavy ion beams as a pumping source may lead to new pumping schemes on the higher lying level transitions and considerably shorter wavelengths, which rely on the high cross sections for multiple ionization of the target species.

The surface flashover behavior in ambient air and nitrogen are studied at a pressure of 1 kg/cm2 using optical emission spectroscopy. A high dc voltage is applied to Rogowski profile electrodes with polyoxymethylene as the insulator between the electrodes. Three different conditions of needle protrusion along the surface of polyoxymethylene are used to study the variation in spectral characteristics due to particle contamination. When the insulator is placed between the spark gap electrodes, the OES spectra are dominated by the Hα line in air and nitrogen medium. It was found that the intensity of N2+ (B-X) emission is less in air surrounding the insulator medium. The plasma temperature during bulk breakdown in air is 0.433 eV, which increases to 0.434 eV with the pressurized nitrogen, which further increases in the presence of insulator to 0.441 eV and 0.44 eV in nitrogen and air, respectively. The electron density is obtained from the N emission line at 746.8 nm and the estimated peak value is 2.85 × 1012 cm−3 in the presence of insulator. The plasma temperature decreases with increase in distance of particle contamination from cathode. The increase in electron density in air, as compared to nitrogen implies more material desorption in air which is also supported by the comparisons of Hα lines.

Within the grand canonical ensemble, we use a general quantum statistical formula and the thermodynamic Green's functions to derive a perturbation expansion for the pressure of a multicomponent plasma. Different contributions to the equation of state (EOS) are given analytically and by numerical calculations. Exact results for the EOS are presented in the shape of a low-density expansion up to the order (ne2)5/2, including ladder-type contributions and “beyond Montroll–Ward” terms.

Flyer acceleration experiments are carried out using a KrF laser system with a pulse duration of 10–15 ns and an intensity of ∼1.0 × 1013 W/cm2. Three-layered targets (aluminum–polyimide–tantalum) are used. First, an average velocity of laser-driven tantalum flyers with a thickness of 4 and 8 μm is estimated. Then, in a collision of a flyer with a copper layer attached to a diamond plate, we measure a transit time of a shock wave in the diamond. The impact velocity is estimated based on the transit time and a numerical simulation. This numerical simulation also shows that the initial peak pressure caused by the impact of a 4-μm-thick flyer is kept at 11 Mbar for 12–13 μm in thickness. Finally, whether this thickness is enough for EOS measurements is discussed.

A new theory for the nuclear forces for confining the nucleons in a nucleus was derived from a generalization of the Debye layer as known from the plasma ablation at laser irradiation where the temperature is substituted by the Fermi energy of the statistics of nucleons. The first convincing proof is by using the empirical density of the nucleons defining their Fermi energy to arrive at a Debye length of about 3 fm as measured by Hofstadter for the decay of the nucleon density at the surface of heavy nuclei. Taking then the surface tension of plasmas with the same steps of substituting temperature by Fermi energy, the surface energy of nuclei is always too small against the nucleon enthalpy to confine the nucleons until equilibrium is reduced at about such high densities reproducing the well known radii of nuclei. The Hofstadter decay can be interpreted as the inhomogeneous wave of the nucleons by Wigner scattering at the nuclear surface similar to the Goos-Haenchen effect. By this way, nuclei are possible only until uranium or curium by a Boltzmann equilibrium process explaining the endothermic generation of heavy nuclei. At about six times higher nucleon density, the Fermi statistics changes into its relativistic branch resulting in a surface energy always smaller than before, and the mass and density independence indicates that one cannot distinguish between the state as in a neutron star or as a quark-gluon plasma. The steps from the ablation of laser produced plasma via a quantum theory of the surface tension in metals to the new nuclear force theory are explained. A consideration of the magic numbers indicates a quark-shell structure of nuclei.

A design for generation of two ultra-high power laser beams, 130 TW and 1.4 PW, using a chain of optical parametric chirped pulse amplifiers, first pumped by a 10 Hz frequency doubled Nd:YAG laser, and later by the frequency tripled single-shot kilojoule level iodine laser Prague Asterix Laser System is presented. Expected enhancement of the parameters in the upgrade, besides the output power, are up to 1022 W/cm2 from 1016 W/cm2 in target intensity, and about 20 fs from 0.5 ns in pulse duration. Owing to the limited dimensions of the Prague Asterix Laser System building, the lay-out of the new equipment had to use only the left-over space in the laser hall.

Iron (Fe) targets are exposed to 100 pulses of Nd: YAG laser (532 nm, 6 ns, 10 Hz) at various fluences ranging from 4.8 to 38.5 J/cm2. In order to explore the effect of background environment, targets have been exposed under vacuum as well as under five different pressures ranging from 5 to 100 Torr of various background gases like Ar, Ne, O2, and air. The sputtering yield measurements and surface modifications of laser-ablated Fe are explored by quartz crystal microbalance (QCM) and scanning electron microscopy (SEM) analysis, respectively. QCM measurements reveal that the sputtering yield of Fe is strongly affected by laser fluence, pressure and nature of gas. By increasing laser fluence, the sputtering yield initially increases due to enhanced energy deposition and then saturates due to self-regulating regime. However, with increasing pressures of background gases, the sputtering yield of Fe initially increases and then decreases. Owing to thermal conductivity, ionization potential, and mass of background gas, the sputtering yield of Fe varies in accordance with the sequence vacuum >Ar>Ne>O2> air. The SEM analysis reveals the formation of several features like laser-induced periodic surface structures, cones, cavities, channels, multiple ablative craters, and dot-like structures. The difference in the periodicity, size, and shape of features is explained on the basis of confinement and shielding effects of plasma and various energy deposition mechanisms. The surface profilometry analysis reveals that the crater depth increases with increasing the laser fluence in inert environments, while in case of reactive environments, it tends to decrease initially and afterwards it increases. X-ray diffraction and energy-dispersive X-ray analyses confirm the oxide formation in case of Fe treatment in O2 and air; however, no additional phases are observed for Fe irradiation under inert environments.

Laser-induced damage threshold is the main limitation for fused silica optics in high-power laser applications. The existence of various defects near the surface is the key factor for the degradation of the threshold. In this work, the photoluminescence spectra at different regions of the damaged and recovered fused silica samples are recorded to analyze the correlation between photoluminescence of surface defects and laser-induced damage threshold. The experimental data concluded the inverse proportional correlation between fluorescence and laser-induced damage threshold value. The weak photoluminescence is the guarantee of the high laser-induced damage threshold, and then the higher local Si nanocluster concentration corresponds with the higher laser-induced damage threshold value for the fused silica optics after CO2 laser treatment. The investigation reveals that photoluminescence measurement can be employed to check the quality of pristine fused silica and evaluate the tendency of the laser-induced damage threshold value. The current results are helpful for understanding the evolution of interaction from CO2 laser treatment and fused silica optics and can provide the guide of process technology for the high quality of fused silica optics.

In this paper, a three-dimensional (3D) model as a new module of LAP3D code is presented to study the crossed-beam energy transfer (CBET) process. This model is not limited by the paraxial approximation and can be used to deal with a large crossing angle case. Besides, this model is also appropriate for the multi-ion species conditions and even multi-beams problems, which will be very helpful in relevant experiment analysis and the target design. In our 3D simulations, we take the overlapped beams with a 60° crossing angle as an example, and observe obvious energy transfer process, which indicates CBET process might occur between the incident laser beams with a large crossing angle when the matching condition is satisfied. This large crossing angle CBET process also can change the spatial shape of the beam spot, and may have some potential important influence on other laser–plasma interaction instabilities and the energy symmetry in hohlraum.

Runaway electrons preionized diffuse discharge (REP DD) could generate volume non-thermal plasmas at atmospheric pressure, thus is widely used for surface modification. In this paper, two pulsed generators are used to produce REP DD for modifying copper (Cu) foil in atmospheric air. One generator produces repetitive pulses with a peak voltage of 40 kV and a rise time of 150 ns. The other generator produces single pulse with a peak voltage of 280 kV and a rise time of 0.5 ns. After the treatment, the modification results for including the macro topography, chemical composition and microhardness in different depths of the Cu surface are analyzed. In order to estimate the modification results in different areas of the Cu foil, several points from the center to the edge of the Cu sample are selected. It could be observed that the maximal modification effect usually appears in the area where the density of the diffuse discharge plasma is highest. The experimental results show REP DD treatment could significantly decrease the water contact angle and increase surface energy of the Cu foil. Meanwhile, it could decrease the carbon concentration and increase oxygen concentration in the near-surface layer of the Cu sample, and enhance the microhardness in different depths of the Cu foil.

The results of the experimental studies of the high-power e-beam accelerator producing six radially convergent electron beams are presented. The studies are aimed to increase the energy of the electron beam transported through the foil into the gas-filled chamber by using the rod-shaped current returns in the diode at small inter-electrode gaps. Installation of these rod current returns shields the periphery regions of the diode from the current field in the central part thus reducing the field at the diode edge. The inter-electrode distance, the shape, and the sizes of the cathodes are chosen by taking into account the magnetic field reduction in the diode. It is shown that in such type of the diode the electrons impact the foil almost normally to its surface, and the electron beams enter the output windows completely. Such type of the diode allows increasing the efficiency of the electron beam energy transfer into the gas by 30%.

When a laser pulse impinges on a molecule which is invariant under certain symmetry operations selection rules for harmonic generation (HG) arise. In other words, symmetry controls which channels are open for the deposition and emission of laser energy—with the possible application of filtering or amplification. We review the derivation of HG selection rules and study numerically the interaction of laser pulses with an effectively one-dimensional ring-shaped model molecule. The harmonic yields obtained from that model and their dependence on laser frequency and intensity are discussed. In a real experiment obvious candidates for such molecules are benzene, other aromatic compounds, or even nanotubes.