Super-luminous ionization front achieved by using axicon as focus lens is proposed to improve the transition-Cherenkov radiation of terahertz emitted from a femtosecond laser filament in air. Benefitted from the better coherent superposition of radiation electric field generated by dipole-like electron current behind the ionization front, the terahertz radiation in far zone is enhanced by one order when the velocity of ionization front exceeds the light speed. Moreover, the radiation spectrum extends toward high frequency and covers the entire terahertz gap.

As the pulse power and high power microwave source technologies gradually matured, technologies for enhancing the output capacities of high power microwaves are becoming more and more attractive. In this paper, two different methods for the increasing of X band microwave powers are discussed: diplexers based on microwave filter and photonic crystal. For the case of diplexer based on microwave filter, the dual channel X band microwaves transmit through the filters with high efficiencies, the polarization and radiation directions for the microwaves are the same. With the application of metal photonic crystal, the reflection and transmission of TE/TM polarized X band microwaves are realized simultaneously; thus, the dual channel microwaves have the same radiation direction. A pulse of 25 ns, 3.9 GW has been successfully obtained. However, according to the experimental results, the internal breakdown in these devices limits their power handling capacities when the peak power and pulse duration of the microwaves increase. In the end, several methods for enhancing the power handling capacities the diplexer have been proposed.

The guiding of a laser beam in a plasma channel formed by a short laser prepulse is investigated. Due to the self defocusing of an ionizing short laser prepulse, the plasma channel formed is axially nonuniform. When a delayed second laser beam is allowed to propagate through such a preformed plasma channel, convergence and divergence of the beam is observed due to the relative competition of the refraction and diffraction phenomenon. We have solved the wave equation governing the propagation characteristics of an ionizing prepulse and a delayed pulse by the moment theory approach. Results have been compared with the paraxial ray model of Liu and Tripathi (1994). The moment theory predicts the propagation of guided laser beam over several Rayleigh lengths.

A new scheme for cone-hollow-assisted fast ignition in inertial fusion is investigated. A hollow is attached to the tip of a conventional gold cone. The transport and heating of the high-current electrons propagating from the cone tip to the compressed fuel core along the hollow is investigated by two-dimensional hybrid simulation. Different hollow geometry sizes are examinized. It is shown that with proper hollow guiding, hot electrons can be collimated between the inner-walls of the hollow by the large interface magnetic fields appearing on the inner surface. When the beam electrons further propagate into the dense region, they are scattered into the gold hollow through collisions with the fuel electrons and ions. The resulting magnetic potential around the hollow then bends beam electrons along the gold hollow to reach the dense core.

The dependence of nanoparticle size distributions on laser intensity profile was determined during infrared femtosecond laser ablation of silver targets in air. Laser parameters were adjusted to ablate at the same peak fluence with spatially homogeneous (flat-top) and inhomogeneous (Gaussian) intensity distributions formed by diffractive optical elements. Aerodynamic particle size was measured online by an electric low-pressure cascade impactor. Narrower size distributions were detected for the flat-top intensity profile in the fluence range from 0.6 to 4.4 J/cm2, while the Gaussian beam produced broad and bimodal distributions. The aerodynamic number frequency of the primary nanoparticulate fraction (40 nm) was equal to the number frequency of the submicron agglomerate fraction (200 nm) at laser fluence of 1 J/cm2. The Feret diameter of primary particles was 80 nm. Geometrical interpretation of the irradiated spots at the corresponding laser fluence regimes explains the formation of bimodal (submicron and nanoparticulate) size distribution in the case of Gaussian beams. The bimodality is attributed to different thermalization pathways during laser ablation.

A model of electron acceleration by an electron Bernstein mode in a parabolic density profile is developed. The mode has a Gaussian profile. It could be excited via the mode conversion of an electromagnetic wave or by an electron beam. As it attains a large amplitude, it axially traps electrons moving close to its parallel phase velocity, where parallel refers to the direction of static magnetic field. As the electrons are accelerated and tend to get out of phase with the wave, the transverse field of the mode enhances its energy and relativistic mass, increasing the dephasing length. The scheme can produce electron energies up to a few MeV.

The analytical evaluation of the capability of Bremsstrahlung highly directional energetic γ-beam to induce photo transmutation of 90Sr (γ,n) 89Sr is presented. Photo transmutation of hazardous nuclear waste of 90Sr, one of the two main sources of heat and radioactivity in spent fuel into valuable nuclear medicine radioisotope of 89Sr is explained. Based on the calculations, a fairly decent fraction of gamma rays in this range are used in transmuting of 90Sr into 89Sr where according to the available experimental data it is shown that by irradiating a 1-cm thick 90Sr sample with lasers of intensity of 1021 W/cm2 and repletion rate of 100 Hz for an hour, the reaction activity would be 1.45 kBq. It is shown that there is not a linear relationship between the growth of the activity and increasing the laser intensity, but there is a dramatic increase in the growth rate especially between 1020and 1021 W/cm2. In this work, the advantage of photonuclear transmutation over the neutron capture transmutation for 90Sr isotope is also discussed.

A 100 kV ion source test stand formerly operated at Lawrence Livermore National Laboratory has been relocated to Princeton Plasma Physics Laboratory, where it is being installed and prepared for operation. A variety of topics relevant to ion-beam-driven high energy density physics and heavy ion fusion will be explored at this facility. The practicality of magnetic insulation to improve the performance of electrostatic accelerators will be investigated by determining whether a pair of parallel plates forming a high-voltage gap can sustain higher electric field gradients, when an electric current is passed through the electrode at the cathode potential so as to produce a magnetic field, which is everywhere parallel to the surface. The facility will also be used to develop and characterize improved plasma sources for space charge neutralization of intense ion beam systems such as the Neutralized Drift Compression Experiment-II facility. The negative halogen ion beam and ion-ion plasma studies previously initiated when this test facility was located at Lawrence Livermore National Laboratory will be resumed, and other experimental topics are also under consideration.

The results of numerical and experimental studies of high-intensity proton beam generation using a 2ω or 1ω Nd:glass laser beam irradiating a thin hydrogen-rich target are reported. The effect of the laser wavelength (λ), intensity (IL) and pulse duration as well as the target thickness, and the preplasma density gradient scale length on proton beam parameters, and the laser-protons energy conversion efficiency were examined by particle-in-cell simulations. Both the simulations and measurements, performed on the LULI 100 TW laser facility at IL up to 2 × 1019W/cm2, prove that at the ILλ2 product fixed, the 2ω laser driver can produce proton beams of intensity, current density and energy fluence significantly higher than the ones which could be achieved using the 1ω driver. In particular, at ILλ2~(0.5–1) × 1020 Wcm−2 µm2 the 2ω picosecond driver makes it possible to generate multi-MeV proton beams of intensity and current density in excess of 1021W/cm2 and 1014A/cm2, respectively, with the conversion efficiency above 10%.

We present a novel waveform synthesized by a half-cycle fundamental wave (800 nm) and a half-cycle subharmonic wave (2400 nm) with an appropriate carrier-envelope phase and a phase delay, in which more ionized electrons can recombine with its parent ions to emit high-order harmonic, giving rise to both the extension of the extreme ultraviolet supercontinuum and the enhancement of harmonic conversion efficiency. An isolated attosecond pulse with considerable energy is obtained as well. By performing time-frequency analyses, it is revealed that the prolonged opposite electric field increases the recombining probability of high-energy electrons.

Proton radiography using laser-driven sources has been developed as a diagnostic since the beginning of the decade, and applied successfully to a range of experimental situations. Multi-MeV protons driven from thin foils via the Target Normal Sheath Acceleration mechanism, offer, under optimal conditions, the possibility of probing laser-plasma interactions, and detecting electric and magnetic fields as well as plasma density gradients with ~ps temporal resolution and ~ 5–10 µm spatial resolution. In view of these advantages, the use of proton radiography as a diagnostic in experiments of relevance to Inertial Confinement Fusion is currently considered in the main fusion laboratories. This paper will discuss recent advances in the application of laser-driven radiography to experiments of relevance to Inertial Confinement Fusion. In particular we will discuss radiography of hohlraum and gasbag targets following the interaction of intense ns pulses. These experiments were carried out at the HELEN laser facility at AWE (UK), and proved the suitability of this diagnostic for studying, with unprecedented detail, laser-plasma interaction mechanisms of high relevance to Inertial Confinement Fusion. Non-linear solitary structures of relevance to space physics, namely phase space electron holes, have also been highlighted by the measurements. These measurements are discussed and compared to existing models.

A fast photo imaging technique has been used to characterize the expansion dynamics of a laser generated silver plasma propagating through background inert gases (He and Ar) at different pressures. The time evolution of the expanding plasma was investigated in the framework of currently available phenomenological models. Mixed-propagation model gives an accurate description of the initial and late plasma expansion stages in Ar when proper input parameters are taken into account. In He, only the initial quasi-linear expansion and shock wave formation were observed along the space available to plasma motion.

Proximity wall stabilized, fast (>4 × 1011 A/s), high current (>40 kA) discharges are capable to create long, dense, hot, stable, non-equilibrium plasma column, suitable e.g., for radiation amplification or even for lasing in extreme ultraviolet and soft X-ray region. Exploding wire in water resembles a metal-vapor-filled capillary with liquid, ever fresh wall (without any metallic deposit). Modeling of wire explosion (inclusive melting and boiling phase transitions, thermal diffusion, and variable conductivity) by the originally skinned driving current is described. Modeling results are compared with measurement of the discharge current and with side-on and end-on monitoring of H-alpha line emission. Analysis of H-alpha line profile is used for diagnostic of water-vapor layer around the wire. The differences between model and reality are attributed to the fact that the pressure dependence of material constants was neglected in the first approximation.

In this paper, the plasma-filling model was extrapolated to the case of a hohlraum driven by a shaped laser pulse, and this extended model was used to obtain an initial design of the hohlraum size. A density criterion of ne = 0.1 was used for designing hohlraums which have low plasma filling with maximum achievable radiation. The method was successfully used to design a half hohlraum size with a three-step laser pulse on SGIII prototype and a U hohlraum size with shaped laser pulse for ignition. It was shown that the extended model with the criterion can provide reasonable initial design of a hohlraum size for optimal designing with a two-dimensional code.

This paper investigates the filamentation process of two co-axially propagating laser beams in collisionless plasma. On account of the ponderomotive nonlinearity, two laser beams affect the dynamics of each other, and cross-focusing takes place. The initial Gaussian laser beams are found to have non-Gaussian structures in the plasma. Using the laser beam and the plasma parameters, appropriate for the beat wave process, the filaments of the laser beams have been studied. Using these results, the Langmuir wave excitation at the beat wave frequency (when the laser beams are having filamentary structures) has been studied. The excited LW is modeled with the help of a driven oscillator and it is found that the excited Langmuir wave is not a plane wave; rather it has a turbulent structure. We have obtained the power spectrum of the excited beat wave (Langmuir wave), and calculated the spectral index. The stochastic electron acceleration has been studied in the presence of this Langmuir turbulence and relevance of these results to the beat wave process has been pointed out.

A scheme capable of enhancing the energy of monoenergetic protons in high intensity laser-plasma interactions is proposed and demonstrated by two dimensional particle-in-cell simulations. The focusing of laser light pulse and the guiding of surface current via the high Z material cone-shaped substrate increase the temperature of hot electrons, which are responsible for the electrostatic field accelerating protons. Moreover, the sub-micron proton layer coated on the cone-shaped substrate makes the total proton beam experience the same accelerating field, thus the monochromaticity is maintained. Compared to the normal film double layer target, the energy of monoenergetic proton beams can be improved about three times.

It is shown that an intense laser pulse can be focused by a conical channel. This anomalous light focusing can be attributed to a hitherto ignored effect in nonlinear optics, namely that the boundary response depends on the light intensity: the inner cone surface is ionized and the laser pulse is in turn modified by the resulting boundary plasma. The interaction creates a new self-consistently evolving light-plasma boundary, which greatly reduces reflection and enhances forward propagation of the light pulse. The hollow cone can thus be used for attaining extremely high light intensities for applications in strong-field and high energy-density physics and other areas.

Energy deposition by high-intensity pulsed ion beam into a metal target has been studied with time-of-flight (TOF) of ions which can be related to the original ion kinetic energy E0 and the ion mass with . It is found that the TOF effect has a profound influence on the kinetic energy distribution of implanted ions and subsequent energy deposition process into the target. The HIPIB of mixed H+ and C+ was extracted from a magnetically insulated ion diode at a peak accelerating voltage of 350 kV, leading to an ion current density of 300 A/cm2 at the target. The widespread ion energy spectrum remarkably varied in shape as arriving at the target surface, from the original Gaussian-like of 80-ns duration to a pulse form of a sharp front and a long tail extending to about 140-ns duration. Energy loss of the mixed ions into a Ti target was simulated utilizing a Monte Carlo method. The energy deposition generally showed a shallowing trend and could be divided into two phases proceeded with sequent arrivals of H+ and C+. Note that, the peak value of deposited energy profile appeared at the beginning of mixed ion irradiation phase, other than the phase of firstly arrived H+ with peak kinetic energy and peak ion current. This study indicated that TOF effect of ions greatly affects the HIPIB-matter interaction with a kinetic energy spectrum of impinging ions at the target, noticeably differing from that of original output of the ion source; consequently, the specific energy deposition phenomena of the widespread ion energy can be studied with the TOF correlation of ion energy and ion current, otherwise not obtainable in common cases assuming fixed ion energy distribution in accordance with the original source output.

We show experimental evidence that, for the intense high-order harmonics from nanoparticles, there is a strong contribution from neutral atoms. We present the results of studies on the harmonics generated in laser-produced plasmas containing various nanoparticles, including Cr2O3, In2O3, Ag, MnTiO3, Sn, Cu, and Au. These results are compared with the harmonics generated from plasma produced on the surface of bulk targets. The harmonic spectrum from nanoparticle and bulk In2O3 show that there is a lack in the resonant enhancement of the 13th harmonic for the former. Along with the relatively low cut-off for nanoparticle harmonics, these results show that it is the neutral atom in the nanoparticle that emits the intense harmonics. Structural studies of plasma debris confirm the presence and integrity of nanoparticles in the plasma plumes.