The results of experiments involving underwater electrical explosion of different wire arrays using an outer metallic cylinder as a shock reflector are presented. A pulse generator with a stored energy of about 6 kJ, current amplitude ≤ 500 kA, and rise time of 350 ns was used for the wire array explosion. The results of the experiments and of hydrodynamic simulations showed that in the case of a Cu wire array explosion, the addition of the reflector increases the pressure and temperature of the water in the vicinity of the implosion axis about 1.38 and about 1.33 times, respectively. Also, it was shown that in the case of an Al wire array explosion with stainless steel reflector, Al combustion results, and, accordingly, additional energy is delivered to the converging water flow generating about 540 GPa pressure in the vicinity of the explosion axis. Finally, it was found that microsecond time scale light emission that appears with microsecond time scale delay with respect to the nanosecond time scale self-light emission of the compressed water in the vicinity of the implosion axis is related to water bubbles formation which scattered light of exploded wires.

The effects of laser incidence angle on lateral fast electron transport at front target surface, when a plasma is preformed, irradiated by intense (>1018 W/cm2) laser pulses, are studied by Kα imaging technique and electron spectrometer. A horizontally asymmetric Kα halo, resulting from directional lateral electron transport and energy deposition, is observed for a large incidence angle (70°). Moreover, a group of MeV high energy electrons is emitted along target surface. It is believed that the deformed preplasma and the asymmetrical distribution of self-generated magnetic field, at large incidence angle, play an important role in the directional lateral electron transport.

In this paper, the influence of the electron flux limiter fe on hohlraum plasmas is studied by using the two-dimensional code LARED-H, and a method to experimentally determine fe via the motion of the M-band emission region in Au hohlraum is proposed. From our simulations, the limited free streaming flux may dominates the heat conduction in the regions with steep temperature gradient, including the laser deposition region, the flux-heated overcritical region, and the laser channel boundary between the hot laser plasmas and the surrounding radiation ablated plasmas, while these are important X-ray emission regions. Hence, the choosing of fe may influence the wall plasma expansion and the laser spot motion, and further influence the motion of the emission regions. From our study, the motion of the M-band (>1.5 keV) emission region is sensitive to fe when the limited free streaming flux dominates the heat conduction of the wall plasma expansion region, and so it is possible to determine fe via the motion of the M-band emission region. In this work, the model used in our simulations is taken from the wall and laser spot motion experiments done by Huser et al. (2009).

Mirror like Molybdenum thin films on SS substrate in vacuum (10−3 Pa) and in Helium environment has been achieved by Pulsed Laser Deposition (PLD) Technique. The PLD thin films of Molybdenum have been characterized by using X-ray Diffraction (XRD) pattern, Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM) and Energy Dispersive X-ray (EDX). The specular reflectivity was recorded with Fourier Transform Infra-Red spectrometer and UV-Visible spectrometer. The optical quality of the thin films was tested via interferometric technique. At the optimum deposition parameters, the crystal orientation was in Mo(110) phase. The FIR-UV-Visible reflectivity of the mirror was found to be closed to that of the polished bulk Molybdenum and Stainless Substrate (SS) substrate.

For a real, meaningful pump-probe experiment with attosecond temporal resolution, an intense isolated attosecond pulse is in demand. For that purpose we report the generation of an intense isolated attosecond pulse, especially in X-ray region using a current-enhanced self-amplified spontaneous emission in a free electron laser (FEL). We use a few cycle laser pulse to manipulate the electron-bunch inside a two-period planar wiggler. In our study, we employ the electron beam parameters of Pohang Accelerator Laboratory (PAL)-XFEL. The RF phase effect of accelerator columns on the longitudinal energy distribution profile and current profile of electron-bunch is also studied, aiming that these results can be experimentally realized in PAL-XFEL. We show indeed that the manipulation of electron-energy bunch profile may lead to the generation of an isolated attosecond hard X-ray pulse: 150 attosecond radiation pulse at 0.1 nm wavelength can be generated.

A large-signal theory of bunching of an intense relativistic electron beam with both velocity and density modulation in the triaxial klystron has been derived in this paper. The theory presents both the harmonic current and the transient velocity in the bunching process, and expresses the velocity modulation directly by the modulation voltage that is easier to be attained and controlled in practice. A few checks are performed on the large-signal theory by particle-in-cell simulation that suggested the large-signal theory of bunching can successfully predict the first-order harmonic current and the velocity on a beam, with both velocity and density modulation, after interacting with a modulation voltage on the order of magnitude with the beam voltage. The theory described in this paper can accommodate general situations such as the bunching of a modulated beam after interacting with a buncher cavity of the Triaxial klystron amplifier.

In this work, it is suggested that the ponderomotive force, induced by a multi-petawatt laser on the interface of a vacuum with solid target, can accelerate a micro-foil to relativistic velocities. The extremely high velocities of the micro-foil can be achieved due to the very short time duration (about a picosecond) of the laser pulse. This accelerated micro-foil is used to ignite a pre-compressed cylindrical shell containing the deuterium tritium fuel. The fast ignition is induced by a heat wave produced during the collision of the accelerated foil with the pre-compressed target. This approach has the advantage of separating geometrically the nanoseconds lasers that compress the target with the picosecond laser that accelerates the foil.

We report on experiments aimed at the generation and characterization of solid density plasmas at the free-electron laser FLASH in Hamburg. Aluminum samples were irradiated with XUV pulses at 13.5 nm wavelength (92 eV photon energy). The pulses with duration of a few tens of femtoseconds and pulse energy up to 100 µJ are focused to intensities ranging between 1013 and 1017 W/cm2. We investigate the absorption and temporal evolution of the sample under irradiation by use of XUV and optical spectroscopy. We discuss the origin of saturable absorption, radiative decay, bremsstrahlung and atomic and ionic line emission. Our experimental results are in good agreement with simulations.

A model of bubble regime electron acceleration by an intense laser pulse in non uniform plasma channel is developed. The plasma electrons at the front of the pulse and slightly off the laser axis in the plasma channel, experience axial and radial ponderomotive and space charge forces, creating an electron evacuated non uniform ion bubble. The expelled electrons travel along the surface of the bubble and reach the stagnation point, forming an electron sphere of radius re. The electrons of this sphere are pulled into the ion bubble and are accelerated to high energies. The Lorentz boosted frame enabled us to calculate energy gain of a test electron inside the bubble.

This work demonstrates the patterning of polymethylmethacrylate (PMMA) by ablation with Ar8+ ion laser (λ = 46.9 nm) pumped by pulse, high-current, capillary-discharge. For focusing a long-focal spherical mirror (R = 2100 mm) covered by 14 double-layer Sc-Si coating was used. The ablated focal spots demonstrate not only that the energy of our laser is sufficient for such experiments, but also that the design of focusing optics must be more sophisticated: severe aberrations were revealed — an irregular spot shape and strong astigmatism with astigmatic difference as large as 16 mm. In some cases, on the bottom of ablated spots a laser-induced periodic surface structure appeared. Finally, an illumination of the sample through quadratic hole 7.5 × 7.5 µm, standing in contact with PMMA substrate ablated from the surface a strongly developed two-dimensional diffraction pattern (period in the center about 125 nm).

A fundamental different mechanism dominates laser interaction with picosecond-terawatt pulses in contrast to the thermal-pressure processes with ns pulses. At ps-interaction, the thermal effects are mostly diminished and the nonlinear (ponderomotive) forces convert laser energy instantly with nearly 100% efficiency into the space charge neutral electron cloud, whose motion is determined by the inertia of the attached ion cloud. These facts were realized only by steps in the past and are expressed by the ultrahigh plasma acceleration, which is more than few thousand times higher than observed by any thermokinetic mechanism. The subsequent application for side-on ignition of uncompressed fusion fuel by the ultrahigh accelerated plasma blocks is studied for the first time by using the genuine two-fluid hydrodynamics. Details of the shock-like flame propagation can be evaluated for the transition to ignition conditions at velocities near 2000 km/s for solid deuterium-tritium.

A two-dimensional theoretical model for the evolution of solid-density plasma irradiated by short, intense laser pulse is introduced. The electrons near the target surface are pushed inward by the radiation pressure, leading to a receding electron density jump where the laser is reflected. The electrostatic field of the resulting charge separation eventually balances the radiation pressure at the laser peak. After that the charge separation field becomes dominant. It accelerates and compresses the ions that are left behind until they merge with the compressed electrons, resulting in a high-density plasma peak. The laser pulse reflected from the receding electron density jump loses energy in plasma and suffers Doppler frequency red-shift, which can provide valuable information on the laser absorption rate and the speed of the receding electrons. Electron oscillations, including the u × B oscillations across the density jump at twice the laser frequency during the laser action, as well as the low-frequency oscillations appearing after laser action, are identified.

As the binary collision process requires much more computation time, a statistical electron-electron collision model based on modified Langevin equation is developed to reduce it. This collision model and a simple electron-ion scattering model are installed into one-dimensional PIC code, and collisional effects on fast electron generation and transport in fast ignition are investigated. In the collisional case, initially thermal electrons are heated up to a few hundred keV due to direct energy transfer by electron-electron collision, and they are also heated up to MeV by Joule heating induced by electron-ion scattering. Thus the number of low energy component of fast electrons increase than that in the collisionless case.

We report numerical results of the linear growth of the Richtmyer-Meshkov instability (RMI) in compressible fluids and in the presence of a magnetic field. These results are obtained with the Lagrangian code LPC-MHD in which media are supposed to be compressible ideal gases. We first applied a magnetic field perpendicular to the wave vector and perpendicular to the shock wave propagation and observed no changes on the perturbation growth velocity compared to the case without magnetic field. We also considered the configuration where the magnetic field is parallel to the wave vector. We observed the stabilization of the instability with oscillations of the perturbations amplitude. Numerical results are compared to impulsive acceleration model of the RMI in the presence of a transverse magnetic field, in the non-compressible limit. A good agreement is obtained between numerical results and model for both the amplitude and the frequency of oscillations. Compressibility seems to have negligible effects.

In the present analysis we study the weakly nonlinear coupled dynamics involving focused radiation beams and space-charge fields in laser-plasmas systems. We direct the analysis to regimes evolving with the co-moving coordinate of the beam frame, but do not make any assumptions on paraxial or underdense conditions. The model thus constructed allows us to investigate equilibrium and nonequilibrium regimes alike. Dependence of equilibrium profiles on control parameters is examined, and beam stability and evolution is investigated as one adds small mismatches to the ideally matched equilibrium. Details of beam evolution depend on initial conditions. However, independently of the precise form of initial conditions, mismatched beams evolve to incoherent space-time patterns.

The results of the development of the ITEP accelerator carbon ion injector based on a repetition-rate CO2 laser ion source are described. The improvement includes a modified pulsed HV-feeding generator for the discharge formation in the laser gas mixture. The advanced discharge module ensures essential increase of the laser active volume and specific electrical deposition energy. The comparative computer simulations of the discharge characteristics for the improved and the prototype lasers are applied. The design and the output spatial-temporal parameters of the free-running laser “Malish-M” are shown, so the significant increase of the laser power is reached. The spatial characteristics of the laser beam obtained with diffraction calculations are compared to measured radial distribution of the energy density. The target laser intensity and the different channels of the energy loss of the laser beam in the optical scheme are estimated. Finally, the output C4+ current trace of heavy ion injector as well as the injector scheme are shown.

The effect of temporal pulse-shape on the characterization of the longitudinal electric field resulting from the tight-focusing of an ultrashort few-cycle TM01 laser beam in free space is investigated analytically and numerically. The longitudinal field is found to be sensitive to the pulse-shape of the driving field. The temporal pulse-shapes considered are Gaussian, Lorentzian, and hyperbolic secant having identical full width at half maximum of intensity. Analytical calculations are made beyond the paraxial and slowly varying envelope approximations. From the numerical results we find that due to finite duration of the signal, the evolution of the pulse envelope before the waist is faster (negative time-delay) but slowed down (positive time-delay) after the waist. This time-delay, for single-cycle pulses of wavelength λ0, and for spot-size w0f in the range 0.6λ0 > w0f > 0.25λ0, is pulse-shape dependent. The time delay is maximum for the Gaussian pulse and minimum for the Lorentzian pulse. The carrier frequency shift depends on the temporal profile of the pulse, beam spot size, axial propagating distance and also on the number of cycles in a pulse. In addition, a comparative study of the variation of the corrected axial Gouy- phase of the longitudinal electric field of single-cycle pulse (spot size w0f = 0.5λ0) with normalized retarded time shows that the phase variation is maximum for Gaussian and minimum for the Lorentzian pulse shape.

The interaction between laser and relativistic electron beams is a promising source of very energetic X rays. We present an accurate model for the collisions between very intense linearly polarized laser beams, corresponding to relativistic parameters of the order of unity or greater, and electrons having energies up to 100 MeV. Our approach uses only one approximation, namely it neglects the radiative corrections. We consider the two cases in which the laser field polarization is either perpendicular or parallel to the plane defined by the directions of propagation of the laser beam and electron beam, and calculate accurately the properties of the σ and π polarized scattered beams. The angle between the directions of the laser and electron beams, denoted by θL, is allowed to have arbitrary values, so that the widely analyzed 180° and 90° geometries, in which the two beams collide, respectively, head on and perpendicularly, are particular cases. We prove that the polarization properties of the scattered beam depend on the angle θL. By varying this angle, the polarization of the scattered beam can be varied between the two limit configurations in which the electromagnetic field of the scattered beam is σ or π polarized with respect to the scattering plane. Our theoretical results are in good agreement with experimental results published in literature. Our model shows that current technologies can be used to produce hard harmonics of the scattered radiations. These harmonics can have relatively high intensities comparable to the intensities of the first harmonics, and energies higher than 1 MeV. Our results lead to the possibility to realize an adjustable photon source with both the energy and polarization of the scattered radiations accurately controlled by the value of the θL angle.

A novel electron acceleration approach with two overlapping linearly polarized laser pulses in vacuum is proposed. By our simulation, the energy and space spreads can reduce greatly comparing with the acceleration with only one laser pulse having doubled peak laser intensity for realistic laser parameters and the average energy gain from our scheme can be doubled for certain pulse lengths, at the same time. Using numerical simulation, analytical criteria for optimal regimes of our acceleration scheme is found.

A comparative study of superficial changes on the superalloy Inconel 600, induced by a picosecond Nd:YAG laser operating at 1064, 532, and 266 nm, is presented. All of the laser wavelengths, as well as the used fluences of 2.5 (1064 nm), 4.3 (532 nm), and 0.6 J/cm2 (266 nm) were found to be adequate for inducing surface variations. Quite different surface features were produced depending on the laser wavelength used. The measured surface damage thresholds were 0.25, 0.13 and 0.10 J/cm2 for 1064, 532, and 266 nm, respectively. Drastic differences, in function of the wavelength used, were recorded for the crater depths, as well the appearance of hydrodynamic effects and periodic surface structures. Differences in crater depths were explained via an easier propagation of the first harmonic laser radiation (1064 nm) through the ejected material and plasma compared to a radiation at 532 and 266 nm. Finally, changes in the surface oxygen content caused by ultrashort laser pulses were considered.