To investigate the influence of pulse repetition rate on the average size of the nanoparticles, nanocrystalline Si films were prepared by pulsed laser ablation in high-purity Ar gas with a pressure of 10 Pa at room temperature, under the pulse repetition rates between 1 and 40 Hz, using a nanosecond laser. Raman, X-ray diffraction spectra, and scanning electron microscopy images show that with increasing pulse repetition rate, the average size of the nanoparticles in the film first decreases and reach its minimum at 20 Hz, and then increases, which may be attributed to the nonlinear dynamics of the laser-ablative deposition. In our experiment conditions, the duration of the ambient restoration, a characteristic parameter being used to distinguish nonlinear or linear region, is about a few seconds from the order of magnitude, which is consistent with the previous experimental observation. More detailed model to explain quantitively the observed effect is under investigation.

A ∼500 kV/400 kA/100 ns pulsed power generator (PPG-I) for x-pinch experiments was designed and constructed at Tsinghua University. It is composed of a Marx generator, a combined pulse forming line (PFL), a gas-filled V/N field distortion switch, a transfer line, and a copper-sulphate resistive load for testing. The PPG-I implements a novel design in lines that four pieces of waterline with impedance 5Ω in parallel constitute a combined PFL with 1.25Ω, and incorporate each other by a common self-break V/N switch on a matched 1.25Ω transfer line. At the peak charging voltage of the PFL, the V/N switch breaks down in multi-channel discharge mode, and electric energy is fed into the testing load through the 1.25Ω transfer line. This article presents the design and test of the PPG-I generator.

The TRIDENT laser system at the Los Alamos National Laboratory is being used for fundamental experiments which study the interaction of self-focusing, stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) in a near-diffraction-limited (single) laser hot spot in order to better understand the coupling between these plasma instabilities. The diffraction limited beam mimics a single hot spot found in speckle distributions that are typical of random or kinoform phase plates (RPP or KPP) used for spatial smoothing of laser beams. A long scale length, hot plasma (∼1 mm, ∼0.6 keV) is created by a separate heater beam, and the single hot spot beam is used to drive parametric instabilities. The focal plane distribution and wave-front of the interaction beam are characterized, and its intensity can be varied between 1014–1016 W/cm2. The plasma density, temperature, and flow profiles are measured using a gated imaging spectroscopy of collective Thomson scattering from the heater beam. Results of the laser and plasma characterization, and initial results of backscattered SRS, SBS, and beam steering in a flowing plasma are presented.

We propose a new time-resolved laser-induced breakdown spectroscopy (TRELIBS) system for quantitative determination of small amounts of pollutants in gas. Some experimental results showing the high resolution of the method are reported, and possible improvements of the system are discussed.

Peculiarities of the technique of the laser-induced film transfer (LIFT) are investigated. Possible mechanisms of tearing-off and transference of the films from the donor substrate (target) to the acceptor one are investigated. The main fields of LIFT applications are considered. One of the most interesting directions of LIFT applications—decontamination of radioactive surfaces—is investigated in detail. The main peculiarities and regimes of the processing are defined.

Resonant acceleration of plasma electrons in combined circularly polarized Gaussian laser fields and self-generated quasistatic fields has been investigated theoretically and numerically. The latter includes the radial quasistatic electric field, the azimuthal quasistatic magnetic field and the axial one. The resonant condition is theoretically given and numerically testified. The results show some of the resonant electrons are accelerated to velocities larger than the laser group velocity and thus gain high energy. For peak laser intensity I0 = 1 × 1020 W cm−2 and plasma density n0 = 0.1ncr, the relativistic electron beam with energies increased from 207 MeV to 262 MeV with a relative energy width around 24% and extreme low beam divergence less than 1° has been obtained. The effect of laser intensity and plasma density on the final energy gain of resonant electrons is also investigated.

Exceptionally high reaction gains of hydrogen protons measured with the boron isotope 11 are compared with other fusion reactions. This is leading to the conclusion that secondary avalanche reactions are happening and confirming the results of high-gain, neutron-free, clean, safe, low-cost, and long-term available energy. The essential basis is the unusual non-thermal block-ignition scheme with picosecond laser pulses of extremely high powers above the petawatt range.

This article reports on experimental studies of subnanosecond electron beams formed in air under atmospheric pressure. An electron beam with an amplitude of ∼170 A with a duration at FWHM of ∼0.3 ns has been obtained. Based on beam temporal characteristics and discharge spatial characteristics, the critical fields were supposed to be reached at plasma approach to anode. Simultaneously, the sharp high-energy pulse of e-beam current is generated. Of critical importance is the cathode type and occurrence on the cathode of plasma protrusions. It is shown that to get maximum amplitude of the electron beam in the gas diode, the discharge in the gas diode should be volumetric.

Basic properties of generation of high-current ion beams using the skin-layer ponderomotive acceleration (S-LPA) mechanism, induced by a short laser pulse interacting with a solid target are studied. Simplified scaling laws for the ion energies, the ion current densities, the ion beam intensities, and the efficiency of ions' production are derived for the cases of subrelativistic and relativistic laser-plasma interactions. The results of the time-of-flight measurements performed for both backward-accelerated ion beams from a massive target and forward-accelerated beams from a thin foil target irradiated by 1-ps laser pulse of intensity up to ∼ 1017 W/cm2 are presented. The ion current densities and the ion beam intensities at the source obtained from these measurements are compared to the ones achieved in recent short-pulse experiments using the target normal sheath acceleration (TNSA) mechanism at relativistic (>1019 W/cm2) laser intensities. The possibility of application of high-current ion beams produced by S-LPA at relativistic intensities for fast ignition of fusion target is considered. Using the derived scaling laws for the ion beam parameters, the achievement conditions for ignition of compressed DT fuel with ion beams driven by ps laser pulses of total energy ≤ 100 kJ is shown.

We focus attention on the combinations of swiftly growing electromagnetic instabilities (EMI) arising in the interaction of relativistic electron beams (REB) with precompressed deuterium-tritium (DT) fuels of fast ignition interest for inertial confinement fusion (ICF). REB-target system is taken neutral in charge and current with distribution functions including target and beam temperatures. We stress also the significant impact on modes growth rates (GR) of mode-mode coupling and intrabeam scattering. Collisional damping is documented at large wave numbers in terms of inverse skin depth. A quasi-linear approach yields lower GR than linear ones. One of the most conspicuous output of the linear analysis are three-dimensional (3D) broken ridges featuring the largest GR above k-space for an oblique propagation w.r.t initial particle beam direction. The given modes are seen immune to any temperature induced damping. Those novel patterns are easily produced by considering simultaneously Weibel, filamentation and two-stream instabilities. The behaviors persist in the presence of smooth density gradients or strong applied magnetic fields. Moreover, in the very early propagation stage with no current neutralization in the presence of large edge density gradients, REB demonstrate a characteristics ringlike and regularly spiked pattern in agreement with recent experimental results and previous simulations.

The use of laser-accelerated protons as a particle probe for the detection of electric fields in plasmas has led in recent years to a wealth of novel information regarding the ultrafast plasma dynamics following high intensity laser-matter interactions. The high spatial quality and short duration of these beams have been essential to this purpose. We will discuss some of the most recent results obtained with this diagnostic at the Rutherford Appleton Laboratory (UK) and at LULI - Ecole Polytechnique (France), also applied to conditions of interest to conventional Inertial Confinement Fusion. In particular, the technique has been used to measure electric fields responsible for proton acceleration from solid targets irradiated with ps pulses, magnetic fields formed by ns pulse irradiation of solid targets, and electric fields associated with the ponderomotive channelling of ps laser pulses in under-dense plasmas.

We consider ion acceleration at the front surface of overdense plasma by a short laser pulse. In this configuration, the laser ponderomotive pressure pushes the background electrons, and a double layer is produced at the boundary of the overdense region. The ions are accelerated by the electrostatic field of the double layer. If the laser intensity is so large that the plasma becomes relativistically transparent, then ion trapping in the running double layer and acceleration to relativistic energies is possible. We study this physics using one-dimensional particle-in-cell simulations. Ion acceleration in one- and two-component plasmas is considered. It is shown that the proton acceleration is more effective when they represent only a small dope to the heavy background ions.

Radiative properties are fundamental for plasma diagnostics and hydro-simulations. For this reason, there is a high interest in their determination and they are a current topic of investigation both in astrophysics and inertial fusion confinement research. In this work a flexible computation package for calculating radiative properties for low and high Z optically thin and thick plasmas, both under local thermodynamic equilibrium and non-local thermodynamic equilibrium conditions, named RAPCAL is presented. This code has been developed with the aim of providing accurate radiative properties for low and medium Z plasmas within the context of detailed level accounting approach and for heavy elements under the detailed configuration accounting approach. In order to show the capabilities of the code, there are presented calculations of some radiative properties for carbon, aluminum, krypton and xenon plasmas under local thermodynamic and non-local thermodynamic equilibrium conditions.

The interaction of high-intensity laser pulses with matter releases instantaneously ultra-large currents of highly energetic electrons, leading to the generation of highly-transient, large-amplitude electric and magnetic fields. We report results of recent experiments in which such charge dynamics have been studied by using proton probing techniques able to provide maps of the electrostatic fields with high spatial and temporal resolution. The dynamics of ponderomotive channeling in underdense plasmas have been studied in this way, as also the processes of Debye sheath formation and MeV ion front expansion at the rear of laser-irradiated thin metallic foils. Laser-driven impulsive fields at the surface of solid targets can be applied for energy-selective ion beam focusing.

Laser-produced plasma (LPP) devices are being developed as a light source for the extreme ultraviolet (EUV) lithography applications. One concern of such devices is to increase the conversion efficiency of laser energy to EUV light. A new idea based on the initiation and confinement of cumulative plasma jet inside a hollow laser beam is developed and simulated. The integrated computer model (HEIGHTS) was used to simulate the plasma behavior and the EUV radiation output in the LPP devices. The model takes into account plasma heat conduction and magnetohydrodynamic processes in a two-temperature approximation, as well as detailed photon radiation transport in 3D Monte Carlo model. The model employs cylindrical 2D version of a total variation-diminishing scheme (for the plasma hydrodynamics) and an implicit scheme with the sparse matrix linear solver (to describe heat conduction). Numerical simulations showed that the EUV efficiency of the proposed hollow-beam LPP device to be higher than the current standard devices.

We report on the results concerning the characteristics and the behavior of expanding plasma generated by a Laser Ion Source (LIS). The LIS technique is an efficient means in producing of multi-charged ions utilizing pulsed laser beams. In order to extract Cu ions, in this experiment an XeCl excimer UV laser was employed, providing a power density on the target surface up to 5 × 108 W/cm2. Two typologies of diagnostic systems were developed in order to detect the plasma current and the ion energy. The time-of-flight (TOF) measurements were performed exploiting either a Faraday cup or an Ion Energy Analyzer (IEA). This latter allowed getting quantitative information about the relative ion abundances, their kinetic energy and their charge state. To study the plasma characteristics we measured the total etched material per pulse at 70 mJ. It was 0.235 μg and the overall degree of ionization, 16%. The angular distribution of the ablated material was monitored by optical transmission analysis of the deposited film as a function of the angle with respect to the normal to the target surface. Applying a high voltage to an extraction gap a multi-charged ion beam was obtained; different peaks could be distinguished in the TOF spectrum, resulting from the separation of ions of hydrogen, adsorbed compounds in the target and copper.

Repetitive nanosecond-pulse discharge with a highly inhomogeneous electric field was investigated in air at atmospheric pressure. Three repetitive nanosecond generators were used, and the rise times of the voltage pulses were 15, 1, and 0.2 ns, respectively. Under different experimental conditions, X-rays and runaway electron beams were directly measured using various setups. The variables affecting X-rays and runaway electrons, including gap distance, pulse repetition frequency, anode geometry, and material, were investigated. It was shown that it was significantly easier to record the X-rays than the runaway electrons in the repetitive nanosecond-pulse discharge. It was confirmed that a volume diffuse discharge was attributed to the generation of runaway electrons and the corresponding X-rays.

A scheme of terahertz radiation generation is proposed by beating of two extra-ordinary lasers having frequencies and wave numbers $\lpar {\rm \omega}_1\comma \; \vec k_1 \rpar $ and $\lpar {\rm \omega}_2\comma \; \vec k_2 \rpar $, respectively in a magnetized plasma. Terahertz wave is resonantly excited at frequency $\lpar {\rm \omega}_1 - {\rm \omega}_2 \rpar $ and wave number (k1 − k2 + q) with a wave number mismatch factor q which is introduced by the periodicity of plasma density ripples. In this process, the lasers exert a beat ponderomotive force on plasma electrons and impart them an oscillatory velocity with both transverse and longitudinal components in the presence of transverse static magnetic field. The oscillatory velocity couples with density ripples and produces a nonlinear current that resonantly excites the terahertz radiation. Effects of periodicity of density ripples and applied magnetic field are analyzed for strong THz radiation generation. The terahertz radiation generation efficiency is found to be directly proportional to the square of density ripple amplitude and rises with the magnetic field strength. With the optimization of these parameters, the efficiency ~10−3 is achieved in the present scheme. The frequency and power of generated THz radiation can be better tuned with the help of parameters like density ripple amplitude, periodicity and applied magnetic field strength in the present scheme.

Heavy ion beam driven implosion of multilayered, single-shell targets for inertial confinement fusion are investigated by ID-simulation. Features characteristic of heavy ion energy deposition are studied. The ion beam energy and the tamper/absorber configuration which give optimum hydrodynamic efficiency and fuel ignition are found for a reactor-size target. A comparison of different pulse shapes with and without prepulse is presented. Implosion by a single-box pulse is found to give superior hydrodynamic efficiency and spherical stability. In addition to these specific results, general features of ion driven implosions are discussed and a brief description of the target code MINIHY is given.

Ag thin films were deposited by pulsed laser ablation in a controlled Ar atmosphere. The deposition process was performed at different Ar pressure values in the range between 10 and 100 Pa to investigate the influence of ambient gas pressure on the plasma expansion dynamics and on the film structural properties. Position, velocity and volume of the laser generated plasma as functions of time were obtained by time resolved fast photography. The morphological properties of the films were investigated by transmission electron microscopy which shows that film growth proceeds via aggregation on the substrates of nanoclusters formed in the expanding plume. The formation of nanoparticles takes place as a consequence of plasma confinement induced by the interaction with ambient gas species. Data from fast photography analysis were used as input parameters to calculate the size of the nanoparticles using a model that takes into account the collisional nature of the laser generated silver plasma.