The nonlinear parabolic partial differential equation governing the evolution of the complex envelope in the slowly varying envelope approximation is solved using the variational approach. The basic nonlinear phenomena of relativistic and ponderomotive self-focusing in a plasma channel are taken into account. Self-focusing, self-phase modulation as well as self-trapping of laser beam is studied in a variety of situations. Further, in the absence of dissipation mechanisms, the stability of the beam is also studied.

A new kind of high power tunable microwave radiation source is studied theoretically and experimentally. Following the previous works presented by Dorranian et al. (2003, 2004) in this paper more details about the radiation is presented. The theory of the radiation is developed to calculate the radiation spatial distribution, and more discussion on radiation behavior and characteristics is done. In this radiation scheme, a part of large amplitude electrostatic plasma wake, generated by an intense laser pulse or a relativistic electron bunch, are converted to electromagnetic oscillations by applying a modest dc magnetic field perpendicular to the wake propagation direction. A direct one-dimensional (1D) analytic procedure for calculating the magnetized plasma wake equations is developed and the properties of the radiation are investigated theoretically. The effects of the ramp plasma-vacuum boundary in coupling the radiation from plasma to vacuum is noticed and solved by employing a gas jet flow to generate a sharp boundary. Wakefield is excited by TW-100 fs Ti:sapphire laser beam operating at 800 nm wavelength. The neutral density of gas jet flow is measured with a Mach-Zehnder interferometer. The frequency of the emitted radiation with the pulse width of 200 ps (detection limitation) is in the millimeter wave range. Radiation is polarized perpendicularly to the dc magnetic field lines and propagates in the forward direction and normal direction with respect to the laser pulse propagation direction, both perpendiculars to the direction of the applied magnetic field. Intensity of the radiation in different plasma densities and different magnetic field strengths has been observed.

We study the motion of a classical relativistic charged particle in the electromagnetic field of a Bessel beam exhibiting vector optical vortices, and show how its dynamical properties, such as linear and angular momentum, are transmitted to the particle. The effects of different polarizations are taken into account using transverse electric and magnetic modes, and their superpositions. The constants of motion are identified for the most general case. We report typical numerical results for axial and radial motion for various configurations, with an estimate of expected axial accelerations when transverse magnetic Bessel modes are used. The Lorentz transformation properties of the field are used throughout in order to simplify the calculations.

A novel coaxial relativistic transit-time oscillator with low guiding magnetic field is proposed and investigated to generate high power microwave at Ku-band. With the coaxial structure and a quasi body wave adopted as the operating mode, the device has a larger space-charge limiting current, higher power handling capacity, and lower guiding magnetic field. Moreover, for further improving the output power, a coaxial TM02 mode resonant reflector is well designed. Main structure parameters of the device are optimized by particle in cell simulations. A typical simulation result is that, with a 358 keV, 7.25 kA beam guided by a magnetic field of about 0.7 T, an 810 MW microwave pulse at 14.25 GHz is generated, yielding a conversion efficiency of about 31%. The primary experiments are also carried out. At a low guiding magnetic field of 0.7 T, a microwave pulse with power of 400 MW, pulse duration of 30 ns, frequency of 14.3 GHz close to the simulation one, and efficiency of 15.4% is generated.

Resonant excitation of terahertz (THz) radiation by nonlinear coupling of two filamented spatial-Gaussian laser beams of different frequencies and wave numbers is studied in plasma having transverse static electric field. The static ponderomotive force due to filamented lasers is balanced by the pressure gradient force which gives rise to transverse density ripple, while, the nonlinear ponderomotive force at frequency difference of beating lasers couples with density ripple giving rise to stronger transverse nonlinear current which results into the excitation of THz radiation at resonance. The coupling is further enhanced by the presence of static electric field and spatial-Gaussian nature of laser beams. An increase of six-fold in the normalized amplitude of THz is observed by applying a direct current field of about 50 KV. Effects of frequency, laser beam width, and periodicity factor of modulated laser amplitude are studied for the efficient THz radiation generation. These results can be utilized for generating controlled tunable THz sources for medical applications using low filament intensities (~ 1014 W/cm2) of beating lasers.

Results of novel experiments with laser-heated capillary targets are presented. In these experiments the interior of gold capillaries having a 200- or 700-μm inner diameter and a 2–12-mm length was axially irradiated by injection of the laser energy through one of the end openings. A frequency-doubled Nd:glass laser (λ = 0.53 μm) was employed, delivering 8-J energy in 3 ns. The experiments showed no significant backreflection of laser light. Depending on the capillary diameter and length, most of the laser energy is either transmitted or absorbed inside the capillary. The transmission of laser light was measured as a function of capillary length and found to be in good agreement with the predictions of a simple theoretical model. Two extreme cases could be identified. Capillaries with a 700-μm diameter show uninhibited laser light propagation due to multireflections off the inner wall. In contrast, at the entrance of capillaries with a 200-μm inner diameter a plasma plug forms that absorbs most of the laser energy. In both cases significant energy transport was observed to occur in the axial direction. A stable and strongly radiating plasma column is formed along the capillary axis by the collision of the radially imploding plasma. During the collision, part of the hydrodynamic energy of the plasma is converted into radiative energy. In a special case-a lower limit of ≊7% could be inferred for the conversion efficiency from laser light into X-ray radiation emitted from the rear opening of the capillary.

Experiments have been performed on the interaction physics of laser light with polystyrene and agar–agar foams having average densities higher than critical. The experiments have been performed at the ABC facility of the Associazione EURATOM-ENEA sulla Fusione, in Frascati. The main addressed topics have been energy coupling (balance), diffusion of energy into the target, plasma and dense phase dynamics, and harmonics generation. The laser light (λ = 1.054 μm) was focused by a F/1 lens to produce on the target surface about 1.6 × 1014 W/cm2 (≈1015 W/cm2 in the waist, set about 100 μm inside the target). Experiments have shown efficient energy coupling (>80%) to be attributed to cavity formation in the low density foam (efficient light absorption) and good mechanical coupling of the plasma trapped in the cavity to the dense phase (ablation pressure work). Heat diffusion possibly plays a transitory role in the initial stages of the interaction (300–500 ps). Time integrated harmonics measurements revealed a blue-shifted 2ω and a red-shifted 5/2ω.

For achieving practically useful laser fusion energy generation, it is necessary to have a M-J laser system with a repetition rate over 10 Hz. We believe that a beam combination method using stimulated Brillouin scattering phase conjugate mirrors (SBS-PCM) is one of the most practical techniques for achieving the high repetition rate of the high power laser. In this paper, we present the recent results about the beam combination laser, such as SBS reflectivity depending on the mode structure, the cross type isolator, and the phase-locking technique. For the phase-locking technique, especially, the self-phase-locking is proposed and its result is discussed.

The one-dimensional problem on bilatiral irradiation by proton beams of the plane layer of condensed DT mixture with length 2H and density ρ0 ≤ 100ρs, where ρs is the fuel solid-state density at atmospheric pressure and temperature of 4 K, is considered. The proton kinetic energy is 1 MeV, the beam intensity is 1019 W/cm2 and duration is 50 ps. A mathematical model is based on the one-fluid two-temperature hydrodynamics with a wide-range equation of state of the fuel, electron and ion heat conduction, DT fusion reaction kinetics, self-radiation of plasma and plasma heating by α-particles. If the ignition occurs, a plane detonation wave, which is adjacent to the front of the rarefaction wave, appears. Upon reflection of this detonation wave from the symmetry plane, the flow with the linear velocity profile along the spatial variable x and with a weak dependence of the thermodynamic functions of x occurs. An appropriate solution of the equations of hydrodynamics is found analytically up to an arbitrary constant, which can be chosen so that the analytical solution describes with good accuracy the numerical one. The gain with respect to the energy of neutrons G ≈ 200 at Hρ0 ≈ 1 g/cm2, and G > 2000 at Hρ0 ≈ 5 g/cm2. To evaluate the ignition energy Eig of cylindrical targets, the quasi-1D model, limiting trajectories of α-particles by a cylinder of a given radius, is suggested. The model reproduces the known theoretical dependence Eig ~ ρ0−2 and gives Eig = 160 kJ for ρ0 = 100ρs ≈ 22 g/cm3.

We study proton acceleration from a foil target with a transversely varying density using multi-dimensional Particle-in-Cell (PIC) simulations. In order to reduce electron heating and deformation of the target, circularly polarized Gaussian laser pulses at intensities on the order of 1022 Wcm−2 are used. It is shown that when the target density distribution fits that of the laser intensity profile, protons accelerated from the center part of the target have quasi-monoenergetic spectra and are well collimated. In our two-dimensional PIC simulations, the final peak energy can be up to 1.4 GeV with the full-width of half maximum divergence cone of less than 4°. We observe highly efficient energy conversion from the laser to the protons in the simulations.

Results are presented for a theoretical model, known as the ion model (IM), recently elaborated to calculate the radiative opacity of a hot dense plasma. The model is based on the self-consistent field method for subsystems obeying Gibbs statistics. The results are compared with calculations that use the Hartree-Fock-Slater model and with experimental data. A theory is proposed to explain the extraordinary spectral line-shift phenomenon associated with such plasmas.

Experimental results are obtained concerning the target polarization, which aptly characterizes the laser ablation. The charge separation in the laser-produced plasma, structure of the ion front, and the current of fast electrons expanding into the vacuum chamber ahead of ions are of crucial importance for the interpretation of multi-peak structure of target currents appearing much later than the laser pulse. Of particular interest is the correlation between the partial maxima in the time-resolved target current and the square root of mass number of ionized species. The late-time negative charging of targets provides evidence for production of very slow ions by ionization of neutrals ablated at the target crater by radiation from plasma produced by 23 ns excimer krypton fluoride laser.

A formulation of radiative transfer is discussed describing energy flow in a turbulent mixture in the vicinity of a Rayleigh–Taylor unstable interface, as might be extant in an ICF pellet. Included in this discussion are (1) the method of smoothing and the Liouville master equation approaches in the case of Markovian statistics as the description of the fluid mixing, (2) the use of asymptotics to derive various limiting descriptions of the Markov model, (3) the use of the theory of alternating renewal processes to obtain an integral equation formulation for non-Markovian statistics, and (4) the reduction of this non-Markovian integral formulation to integro-differential equations of the generic transport form, with statistical effects represented by pseudoscattering terms.

Three types of multilayer flyer energy conversion elements (MFECEs) through integrating different laser pulse absorption/ablation layer of nano-film materials into a laser-driven flyer plates between thermal barrier of alumina and transparent substrate have been investigated in this study. The relationships among the velocity of flyer plates, initiation performance of hexanitrostilbene (HNS-IV), and initiation energy were analyzed, comparing with single-layer Al flyer plate. The photonics Doppler velocimetry and James criterion were utilized in the experiments to characterize the velocity of flyer plates and shock initiation of laser-driven flyer detonator, respectively. The surface reflectivity measurements of the Al, C/Al and Mg/Al layers were performed using laser reflectivity. HNS-IV without initiation was analyzed by scanning electron microscope and energy dispersive spectrometer. Caused by aluminum/alumina/aluminum (Al/Al2O3/Al) flyer plate, the residual fragments were found in the pit on the surface of charge. The results obtained were shows that three types of multilayer flyer plates can initiate HNS-IV successfully under the lower laser pulse energy, although all four kinds of flyer plates have successfully initiated HNS-IV with laser pulse energy in the range of 53.80–166.80 mJ. Changing the ablation layer structure and adding thermal insulation layer to the multilayer flyer plates, reduces the shock initiation laser pulse energy of HNS-IV to 53.80 mJ. The laser-driven flyer detonator has significant advantages in providing safety and reliability, especially in a strong electromagnetic environment. The MFECEs of laser-driven flyer detonator exhibited a high level of integration and proved to have promoted laser-driven energy coupling rate, which can significantly be used to improve the performance of the laser-driven flyer detonator in military and civilian applications.

Results are presented of experiments on ion production from Ta targets using a short pulse (350–600 ps in focus) illumination with focal power densities exceeding 1014 Wcm-2 at the wavelength of an iodine photodissociation laser (1.315 μm) and its harmonics. Strong evidence of the existence of tantalum ions with the charge state +45 near the target surface was obtained by X-ray spectroscopy methods. The particle diagnostics point to the existence of frozen high charge states (<53+) of Ta ions in the far expansion zone at about 2 m from the target. The measured charge state-ion energy distribution indicates the highest energy (>4 MeV) for the highest observed charge states. A tentative theoretical explanation of the observed anomalous charge state freezing phenomenon in the expanding plasma produced by a subnanosecond laser pulse is given.

New results obtained in experiments on laser irradiation (I = 5 × 1013 W/cm2, λ = 1.054 µm) of low-density (2–10 mg/cm3) porous materials (agar, triacetate cellulose, and foam polysterene) are presented and discussed from the standpoint of optimum porous material utilization in target designs for inertial confinement fusion. The influence of low-density material microstructure of irradiated samples on the absorption of laser radiation and the energy transfer processes was investigated using X-ray and optical diagnostic methods with high temporal and spatial resolution.

This paper presents a scheme for second harmonic generation (SHG) of q-Gaussian laser beam in plasma channel created by ignitor heater technique. The ignitor beam creates plasma by tunnel ionization of air. The heater beam heats the plasma electrons and establishes a parabolic density profile. The third beam (q-Gaussian beam) is guided in this plasma channel under the combined effects of density nonuniformity of the plasma channel and relativistic mass nonlinearity of the plasma electrons. The propagation of q-Gaussian laser beam through the plasma channel excites an electron plasma wave at pump frequency that interacts with the incident laser beam to produce its second harmonics. The formulation is based on finding the numerical solution of the nonlinear Schrodinger wave equation for the fields of the incident laser beams with the help of moment theory approach. Particular emphasis is put on dynamical variations of the spot size of the laser beams and conversion efficiency of the second harmonics with distance of propagation.

In the present research work, the authors have investigated the self-focusing and defocusing of Hermite-cosh-Gaussian laser (HChG) beam in an inhomogeneous rippled density plasmas. By taking the relativistic non-linearity into account, an equation for envelope is set up and solved using Wentzel–Kramers–Brillouin and the paraxial ray approximation. An ordinary non-linear differential equation governing the beam width parameter as a function of propagation distance is set up for different mode structures of the beam. Further, a numerical study of this differential equation is carried for suitable set of plasma and laser parameters. The beam undergoes periodic self-focusing/defocusing due to relativistic non-linearity. We also report the comparison between self-focusing/defocusing of HChG beam in the absence and presence of density ripple. Presence of ripple does not only leads to substantial increase in self-focusing length, but also results in oscillatory character with decreasing f. In a relativistic case, strong oscillatory self-focusing and defocusing is observed. Further, self-focusing is enhanced with increased value of decentered parameter.

Based on transferring energy from multiple pump beams into one Stokes beam using Brillouin amplification, a serial coherent laser beam combination scheme is presented, which has many advantages, such as, simple structure, low cost, ease of adjustment, higher load capability, scalable easily, etc. Furthermore, it has been demonstrated that the combination of several beams using this method is theoretically possible. But in practice, the amplification of high power Stokes beam is a key problem to solve. In this paper, the amplification of Stokes beam whose power is higher than the pump beam is first studied and proved experimentally. Coupling the two laser beams by this method is proved experimentally, and the coupling efficiency reaches more than 80%. Then the feasibility of multiple beams combination based on Brillouin amplification is analyzed and tested theoretically.

Analysis and simulations of fast particles produced by a high-intensity short laser pulse interacting with a foil target are performed. Initially, the plasma density distribution of the foil target has a smooth gradient with the scale length of plasma density varying across it. The absorbed laser energy is transferred to fast electrons, which penetrate in the foil and are partially ejected from the foil rear. These electrons produce an electric field that causes an ion beam to be emitted from the foil. We analyze the mechanism of ion acceleration in the foil plasma and the influence of the density gradient and other laser and plasma parameters on ion acceleration. The angular distributions of the ejected electrons and ions are calculated.