A scheme of resonant terahertz (THz) radiation generation by non-linear beating of two lasers in hot magnetized plasma with step density profile is investigated. Beating lasers of frequency difference ω1 − ω2 ≈ ωp(~1 THz) is incident obliquely on plasma surface and exerts non-linear ponderomotive force on plasma electrons. The plasma electrons start oscillating in the plane of incidence and give rise to space charge field to maintain plasma neutrality. In turn, both ponderomotive force and space charge field excites a non-linear surface current, responsible for THz radiation generation on the reflection side. The coupling between plasma wave and electromagnetic wave present (inside the plasma as well as on reflection side) becomes stronger in the presence of the transverse DC magnetic field. THz radiation amplitude is optimized at an angle of incidence θ ~ 50–70°.

We report utilization of the laser induced forward transfer technique to re-deposit indium thin films onto the accepter substrate using nJ laser pulses from a femtosecond laser oscillator. Keeping the accepter substrate stationary enables dots of Indium to be deposited; in contrast, linear motion of the accepter substrate facilitates deposition of lines of Indium. The effect of laser pulse energy on the deposition process is studied. The effect of translation speed of donor substrate on the laser induced forward transfer pattern is also probed and an upper limit of translation speed is established beyond which smearing is observed to occur.

The paper presents experimental and theoretical research data on the generation, transport, and extraction of a large cross-section (750 × 150 mm2) electron beam into the air through a thin metal foil in an accelerator with a mesh plasma cathode on the bases of a low-pressure arc and with a multi-aperture two-electrode electron-optical system. When the burning conditions of the arc discharge, responsible for the generation of the emission plasma, is changed, the characteristics of this plasma were investigated, including under the conditions of the selection of electrons from it. Our experiments show that at an accelerating voltage of 200 kV, current in the accelerating gap of up to 30 A, and full width at half maximum of up to 100 µm, the average extracted power is ≈4 kW and the extracted beam current is ≈85% from the common current into the accelerating gap. Our numerical estimates give a good correlation between the arc and emission plasma parameters depending on the electrode configuration in the discharge system and on the mechanism of electron beam generation. Analysis of the emission plasma parameters under different arc conditions and of the mechanisms responsible for the beam energy loss suggests that most of the energy in the accelerator is lost at the support grid and at the output foil due to defocusing of the beam and partial electron reflection from the foil. Other mechanisms that decrease the extracted beam energy are discussed.

Both broad and narrow band Nd glass laser beams with energies 1 to 3 joules and pulse width 150 ps were used in aluminium plane target experiments at laser irradiances 1 to 3 × 10 14 W cm −2 on target surfaces. The incident laser beams were angled at 0°, 7·2°, 14·4°, 21·6°, 28·8°, 36°, 43·2° to the target surface normal and the polarization was perpendicular or parallel to the incident plane (s or p polarization). The experiments showed that the maximum resonance absorption occurred near to incident angles of about 9° to 10° and the broadband resonance absorption was slightly smaller than that of the narrowband. At large incident angles the broadband absorption was larger than that of the narrowband.

Our earlier papers demonstrate a very simple method of plasma jet formation, consisting in irradiating a massive planar target of a relatively high atomic number by a partly defocused laser beam. Our present interest is concentrated on interaction of the plasma jet with other media. This paper is aimed at investigations of interaction of two jets launched successively on Cu target. Our attention was paid to the role of radiative cooling in the plasma jet formation. The experiment was carried out at the PALS iodine laser facility. The laser provided a 250-ps (full width at half maximum) pulse with energy of 130 J at the third harmonic frequency (λ3 = 0.438 µm). Two successive jets were produced on a massive flat Cu target provided with a cylindrical channel 5 mm long and 400 µm in diameter. Since the focal spot diameter of the laser beam on the target surface was larger than that of the channel (800 µm), the annular irradiation of the target face resulted in creation of the first plasma jet, whereas the second jet was produced by action of the central part of laser beam on the channel wall. Three-frame interferometric system, X-ray streak camera, and a set of ion collectors were used as diagnostic tools.

In an earlier preliminary design study, we proposed a novel nuclear-pumped laser-driven (NPL) inertial confinement fusion (ICF) power reactor that represents an important variation on the “neutron feedback” concept for ICF. This NPL-driven ICF concept also included an advanced, DT-seeded, D3He-fueled pellet and magnetic protection of the first wall of the reactor chamber. Advantages that were demonstrated for this approach included increased efficiency for laser-to-target energy coupling, increased efficiency for thermalto-electric energy conversion, and reduced neutron activation and waste. The coupling efficiency is enhanced because a nuclear-pumped flashlamp is directly pumped by fission fragments from uranium micropellets within the lamp medium. The thermal conversion efficiency is greater because a large fraction of the ICF pellet&s fusion yield is in charged Finally, the fraction of the fusion yield carried by neutrons is significantly reduced in comparison with pure D-T-fueled pellets; thus, neutron-induced activity in the first wall is decreased and safety is increased. The initial study indicated these factors could result in a required driver energy of 5 MJ (vice 10 MJ currently projected) and a pellet gain of only 50 (vice 100 currently projected) for a feasible l,000-MWe power reactor operating with approximately six pellets per second. The current study includes a refined analysis of an NPL-driven ICF power reactor of this type. A cylindrical design for the fission/NPL blanket is selected as a “natural” geometry for pumping the NPL. Required enrichments and criticalities are then predicted for the multiplication of the fusion neutron yield needed to pump the NPL. Based upon these results, we report a more detailed parametric study of the efficiencies for converting neutron, X-ray, and plasma yields from advanced ICF pellets into electrical and optical energy flows required in this concept. We also examined breeding tritium in a lithium blanket layer. Results from these studies help define topics and parameter spaces for further research on this unique reactor concept.

Numerical simulation of active media nuclear-pumped lasers on noble gases and their mixtures with metal vapors are presented. Prospects of creation of high-power short-wavelength nuclear-pumped excimer lasers are discussed.

For ultrafast material analyses, we constructed the time-resolved X-ray diffraction system utilizing ultrashort X-rays from laser-produced plasma generated by the 12-TW–50-fs laser at the Nuclear Engineering Research Laboratory. Ultrafast transient changes in laser-irradiated GaAs crystals were observed as X-ray diffraction patterns. Experimental results were compared with numerical analyses.

The paper considers the equation for heterogeneity coefficient within the turbulent mixing area in the approximation of big Reynolds numbers and small Mach numbers. A mechanism is studied of the heterogeneity coefficient dissipation due to molecular diffusion. The Kolmogorov's hypothesis on developed turbulence is used to calculate a dissipative term. The model presented allows us to take into account the heterogeneity degree in LV- and KE-models of turbulent mixing. A system of equations allowing us to calculate directly the heterogeneity degree is derived for the case of the LV-model with the turbulent diffusion coefficient which is constant over the turbulent mixing area. A self-similar solution is derived for the heterogeneity coefficient which is in good agreement with the results of experiments and direct numerical simulations. The heterogeneity coefficient averaged over the mixing area is shown to depend weakly on the density drop between the mixing materials. Thus, it is kH = 0.25 at the drop n = 1–3, and at the drop n = 20 − kH = 0.23.

It is demonstrated that finite pressure gradients can be maintained in the lowest free energy state (‘relaxed state’) of a plasma configuration. The pressure forces are supported by the Magnus Force in a compressible adiabatic plasma if mass motions are considered. It has been demonstrated elsewhere that these forces can be of the same order of magnitude as the Lorentz forces in some laboratory plasmas.

A hybrid configuration of a heat-capacity laser (HCL) and a moving-slab laser (MSL) is proposed. Multiple volumes of solid-state laser material are sequentially diode-pumped and their energy extracted. When a volume reaches a maximum temperature after a “submagazine depth,” it is moved out of the pumping region into a cooling region, and a new volume is introduced. The total magazine depth equals the submagazine depth times the number of volumes. The design parameters are chosen to provide high duty factor operation, resulting in effective use of the diode arrays. The concept significantly reduces diode array cost and is considered enabling for many potential applications.

Laser induced ablation studies have been carried out on formation of amorphous carbon and graphene on SiC thin films with their detailed characterization studies. Pulse laser ablation technique with process parameters such as 248 nm KrF excimer laser, frequency 10 Hz, 200 mJ of laser energy, and chamber pressure of 7 × 10−6 mbar has been used. Films were characterized in detail by grazing incidence X-ray diffraction, Fourier transform infrared, micro-Raman, X-ray reflectivity, Field emission scanning electron microscopic, transmission electron microscope, and Nano-indentation techniques and the results are reported. As deposited SiC film surface is rich in amorphous carbon and the same has been used as the nucleation site for further growth of graphene on SiC films. Film hardness increased from 29 GPa to 37 GPa for SiC film and graphene on SiC film (C-SiC), respectively. These films show bands due to surface phonon polariton mode in the range of 810–840 cm−1 that is a research concern today in nano-photonics area. Further these materials find applications in understanding the laser irradiation effects on SiC based nuclear fusion wall material.

In order to use two paralleled X-pinches as X-ray sources for the time-resolved backlighting of wire-array Z-pinch plasma, it is necessary to make these two X-pinches emit X-rays at different but roughly preset time instants. The timing of the X-ray burst from an X-pinch independence of the current, and the wire mass of the X-pinch was investigated. The currents flowing through two paralleled X-pinches were measured and it was found that the total current is almost equally divided between these two X-pinches no matter how different the wires for these two X-pinches are. The reason for the equal current division between two paralleled X-pinches was given based on the inductance calculation of the X-pinch circuit.

An experimental investigation on X-ray emission from laser-produced plasmas is presented and the properties of such an emission of interest for application purposes are examined. Plasmas were generated by focusing 1 μm, 3 ns Nd laser pulses onto Al and Cu targets at an intensity of 1013 W/cm2. The temporal evolution of the emission and its spectral features were investigated by using an X-ray streak-camera and an X-ray photodiode. In the case of Cu targets, the analysis of the emission showed two spectral components. The main component was centered at ≈ 1.2 keV and a minor component, whose intensity was measured to be 10-3 of the previous component, was observed at ≈7 keV. The X-ray conversion efficiency, in the investigated spectral region, was measured to be 1% for Cu targets and 0.3% for Al targets.

A scaling model for hot spherical ablative implosions in direct-drive mode is presented. The model results have been compared with experiments from LLE, ILE, and LLNL. Reduction of the neutron yield due to illumination nonuniformities is taken into account by the assumption that the neutron emission is cut off when the gas shock wave reflected off the center meets the incoming pusher, i.e., at a time when the probability of shell breakup is greatly enhanced. The main advantage of this semiempirical scaling model is that it elucidates the principal features of these simple implosions and permits one to estimate very quickly the performance of a high-aspect-ratio direct-drive target illuminated by short-wavelength laser light.

This paper is an extension of our previous paper (Mašek and Rohlena, 2015), where we applied a transform method for the solution of Vlasov–Maxwell set of equations in a one-dimensional geometry to describe the Raman backscattering of the heating ns laser wave in the external corona of the generated laser plasma in a strongly non-linear regime. The method is stabilized by a simplified Fokker–Planck collision term, which, in turn, is used for a study of the influence of collisional and collisionless damping mechanisms of the daughter electron plasma wave (EPW) on the instability development and their competition resulting in a different instability behavior in various plasma configurations. The physics of trapped electrons is studied in detail and compared to the resulting Raman reflectivity. The Raman reflectivity was found to depend strongly on the intensity of laser irradiation in the different regions of the plasma corona. This is discussed in detail from the point of view of trapped electrons behavior in the EPW. Moreover, a study of the Raman reflectivity dependence on the electron–ion collision frequency (average plasma ionization) is presented, too. The results supplement the physical picture of the collision and collisionless processes influencing the Raman instability non-linear development.

A model of an electron beam interacting with neutral argon was developed by solving the chemical kinetic rate equations for the time-dependent populations of ground and excited levels of Arl and Aril as well as the populations of electron energy groups. Intensities of spectral lines were calculated, from predicted population densities and Einstein coefficients, and compared to experimental results.

The thermal plasma is generated during the beam pulse and persists for some time after the pulse is terminated. Low energy levels of Arii with a 4s or 4p valence electron have similar time profiles to the plasma density. However, high energy levels of Aril with a 4p′ or 4p′ valence electron have similar temporal profiles as the beam current. They are populated predominantly by direct ionization and exceed levels populated by thermal electrons. The 4p′ levels decay rapidly to 4s′ levels, which have very high beam deposition efficiencies for being pumped back to the 4p′ levels. In this way, certain transitions such as 4s′–4p′ in ArII are pumped directly by the electron beam. Without direct ionization, these transitions would be negligible compared to those transitions which have lower energy levels.

Electromagnetic emission at the plasma frequency ωp and its harmonics nωp has been studied. Although such emission is well known from very low density plasmas (electron density of the order of ne ≈ 108 cm−3) now, for the first time it has also been observed from a high density plasma (electron density of the order of ne ≈ 1023 cm−3) produced by a high-intensity femtosecond laser pulse. This radiation is strongly connected to jets of high energy electrons produced in such steep gradient plasmas by collective mechanisms, and probably to nonlinear Langmuir waves in the overdense plasma region. Theoretical investigations using particle-in-cell simulations have been made to pinpoint the physical origin and properties of the emission. Preliminary results show a very weak scaling of the ωp and 2ωp emission with intensity, which should provide clues for future theoretical analyses. Although not the main subject of the present work, also harmonics up to the 20th of the laser fundamental may have been observed close to the ωp and 2ωp line emission in the present experiment (PACS numbers: 52.40.Nk, 42.65.ky, 52.65.-y, 33.20.Ni, 52.25.Qt).

Experiments to demonstrate the effects of various beam-smoothing techniques have been performed on the 60-beam, 30-kJ UV OMEGA laser system. These include direct measurements of the effect beam-smoothing techniques have on laser beam nonuniformity and on both planar and spherical targets. Demonstrated techniques include polarization smoothing and “dual-tripler” third-harmonic generation required for future broad bandwidth (∼1 THz) smoothing by spectral dispersion (SSD). The effects of improvements in single-beam uniformity are clearly seen in the target-physics experiments, which also show the effect of the laser pulse shape on the efficacy of SSD smoothing. Saturation of the Rayleigh-Taylor (RT) growth of the broad-bandwidth features, in agreement with the Haan model (Haan, 1989), produced by laser imprinting has also been observed.