An investigation is made of the role of hollow atoms in the spectra of an ultrashort-pulse-laser-driven Ar cluster target. Experimental measurements are presented from an Ar cluster-gas target using short-pulse lasers with various intensities, durations, and contrasts. Calculations in support of these measurements have been performed using a detailed atomic kinetics model with the ion distributions found from solution of the time-dependent rate equations. The calculations are in good agreement with the measurements and the role of hollow atoms in the resulting complicated spectra is analyzed. It is demonstrated that, although the presence of hollow atoms is estimated to add only around 2% to the total line emission, signatures of hollow atom spectra can be identified in the calculations, which are qualitatively supported by the experimental measurements.

The plume images of the laser produced silver plasma in the absence and presence of 0.45 T transverse magnetic field has been investigated under vacuum ~10−4 torr and in air. An Nd:YAG laser (1.064 µm, 1.1 MW, 9 ns) with intensity ~1012 Wcm−2 was used to generate plasma. A CCD image capture system was used for plasma imaging to explore the plume. A magnetic probe was employed to measure the variation in internal magnetic field of plasma with as well as without 0.45 T external transverse magnetic field. The X-ray emission from plasma in both the cases (with and without B field) was also monitored using two PIN photodiodes filtered with 24 µm Cu and 24 µm Al. The plume images in both the cases were then correlated with the time resolved soft X-ray emission. It was found that the self generated magnetic field of the plasma increases in the presence of magnetic field. Plume images reveal that the confinement of the plume takes place in the presence of magnetic field both in the cases of air and vacuum. Jet and spikes like structures were also observed due to plasma instabilities. Lobe formation in the plume at latter stages of plasma evolution was more prominent in air than under vacuum. X-ray emission signals exhibited an enhancement in the emission under transverse magnetic field. An increased rate of recombination due to high density as a result of plasma confinement across the applied magnetic field was found to be the main reason behind emission enhancement.

The properties of beams of high energy protons accelerated during ultraintense, picosecond laser-irradiation of thin foil targets are investigated as a function of preplasma expansion at the target front surface. Significant enhancement in the maximum proton energy and laser-to-proton energy conversion efficiency is observed at optimum preplasma density gradients, due to self-focusing of the incident laser pulse. For very long preplasma expansion, the propagating laser pulse is observed to filament, resulting in highly uniform proton beams, but with reduced flux and maximum energy.

Capsules with a thin aerogel shell were prepared by the OO/W/OI emulsion process. (Phloroglucinol carboxylic acid)/formaldehyde (PF) was used as the water phase (W) solution to form the shell of the capsule. PF is a linear polymer prepared from phloroglucinol carboxylic acid. The viscosity of the PF solution can reach a high level of 9×10−5 m2/s without gelation while resorcinol/formaldehyde (RF) gelates at ~3–4×10−5 m2/s. Using the viscous PF solution, capsule with a 17 µm gel shell was fabricated. This thickness satisfies the specification of the first phase of Fast Ignition Realization Experiment (FIREX-I) at Osaka University. When PF gel was extracted to remove the organic solvent, shrinkage of 9% occurred. The final density of the PF aerogel was 145 mg/cm3. Both the shell thickness and density can satisfy the specification of FIREX-I. The pore size of the PF aerogel was less than 100 nm while that of RF was 200–500 nm. The SEM showed that PF had particle-like foam structure while RF had fibrous-like foam structure.

A scheme is proposed for the acceleration of electrons generated during the ionization of a gas by two laser pulses. The electrons created from the ionization of neutral atoms near the rising edge of the pulse do not gain sufficient energy. If a prepulse is used before the main pulse then the prepulse removes electrons from the outer shells, and the main laser pulse interacts with the electrons in the inner shells of high atomic number gases, such as krypton and argon. The electrons are generated close to the peak of the main laser pulse and gain energy in GeV with a small spread in the energy and low emittance angle.

Laser interactions with mass-limited targets are studied here via numerical simulations using our relativistic electromagnetic two-dimensional particle-in cell code including all three-velocity components. Analytical estimates are derived to clarify the simulation results. Mass-limited targets preclude the undesirable spread of the absorbed laser energy out of the interaction zone. Mass-limited targets, such as droplets, are shown here to enhance the achievable fast ion energy significantly due to an increase in the hot electron concentration. For given target dimensions, the existence is demonstrated for an optimum laser beam diameter when ion acceleration is efficient and geometrical energy losses are still acceptable. Ion energy also depends on the target geometrical form and rounded targets are found to enhance the energy of accelerated ions. The acceleration process is accompanied by generation of the dipole radiation in addition to the ordinary scattering of the electromagnetic wave.

Laser induced breakdown spectroscopy is a fast non-contact technique for the analysis of the elemental composition of any sample. Our focus is to advance this technique into a regime where we use pulse energies below 100 µJ. This regime is referred to as micro-laser-induced breakdown spectroscopy or µLIBS. At present we have concentrated on two application areas : (1) The imaging of latent fingerprints and (2) the extension to laser ablation followed by laser-induced fluorescence (LA-LIF) for very high sensitivity analysis of contaminants in water. Preliminary pulse emission scaling of Na in latent fingerprints has been investigated for ~130 fs, 266 nm pulses with energies below 15 µJ. The lowest energy for reliable single shot detection of Na is approximately 3.5 µJ. A 2D map of a fingerprint on a Si wafer has been successfully demonstrated using 5 µJ pulses. In LA-LIF the detection sensitivity of micro-laser-induced breakdown spectroscopy (µLIBS) is improved by coupling it with a second resonant probe pulse. This technique was investigated for the detection of Pb at low concentrations when ablated by 266 nm, 170 µJ pulses. After a short delay the resulting plume was re-excited with a nanosecond laser pulse tuned to a specific transition of Pb. In the case of the resonant dual-pulse LIBS the limit of detection was found to be approximately 60 ppb for Pb in water for 1000 shots. It is expected that this result could be implemented with fiber or microchip lasers with multi-kHz repetition rates and fiber Bragg grating tuning elements. The results are promising for the development of portable µLIBS water monitoring systems and portable fingerprint scanners.

The temporal and spatial X-ray emission from PPG-X, an X-pinch driven by pulsed power generator, was studied by using diamond photo-conducting detectors and pinhole cameras. It was found that the X-ray pulse usually consists of two sub-nanosecond peaks with a time interval of about 0.5 ns, these two X-ray peaks are consistent with two point sources of X-ray recorded with pinhole camera. The total X-ray energy changes from shot to shot and is averaged to be 0.35 J for hν > 1.5 keV. The size of the X-ray point source is in the range from 100 µm to 5 µm, decreasing rapidly with the increase of the photon energy. The X-pinch was used as X-ray source for backlighting the electrical explosion of single wire and for phase-contrast imaging of a mosquito.

We study the generation of high-order harmonics from plasma plume, by using the 20 TW, 10 Hz laser of the Advanced Laser Light Source (ALLS). We perform detailed studies on enhancement of single high-order harmonics generated in laser plasma using the fundamental and second harmonic of the ALLS beam line. Quasi-monochromatic harmonics are observed for Mn, Cr, Sb, Sn, and In plasmas. We identify most of the ionic/neutral transitions responsible for the enhancement, which all have strong oscillator strengths. Intensity enhancements of the 13th, 17th, 21st, 29th, and 33rd harmonics from these targets are demonstrated using the 800 nm pump laser and varying its chirp. We also observed harmonic enhancement from some targets for 400 nm pump laser. Using Mn plume, we demonstrated the highest harmonic photon energy (52.9 eV) at which enhancement has been observed (17th order, λ = 23.5 nm).

This paper reports on the properties of a supershort avalanche electron beam generated in the air or other gases under atmospheric pressure and gives the analysis of a generation mechanism of supershort avalanche electron beam, as well as methods of such electron beams registration. It is reported that in the air under the pressure of 1 atm, a supershort (<100 ps) avalanche electron beam is formed in the solid angle more than 2π steradian. The electron beam has been obtained behind a 45 µm thick Al-Be foil in SF6 and Xe under the pressure of 2 atm, and in He, under the pressure of about 15 atm. It is shown that in SF6 under the high pressure (>1 atm) duration (full width at half maximum) of supershort avalanche electron beam pulse is about 150 ps.

Fast ignition for fusion energy by using petawatt-picosecond (PW-ps) laser pulses was modified due to an anomaly based on extremely clean suppression of prepulses. The resulting plasma blocks with space charge neutral ion current densities above 1011 Amp/cm2 may be used to ignite deuterium-tritium at densities at or little above solid state density. The difficulty is to produce extremely high energy flux densities of the blocks. Results are reported how the threshold can be reduced by a factor up to fife if the inhibition factor for thermal conductivity due to electric double layers is included in the hydrodynamic analysis.

The paper is devoted to research and development of a novel experimental technique—liquid-filled laser-driven shock tube (LST) for modeling of Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) hydrodynamic instabilities development at the contact surface of two immiscible liquids under shock wave (SW) passage. 100-J, 100-ns KrF laser facility GARPUN has been used to irradiate some opaque liquids. A homogenizing focusing system combined multi-element prism raster and a lens to provide non-uniformity less than a few percents across a square 7 × 7-mm spot, laser intensities being varied in the range of q = 0.004–2 GW/cm2. Surface plasma blow-off produced a planar SW, which propagated into the liquid. SW amplitudes as high as 0.8 GPa weakly damping with increasing thickness were measured in dibutyl-phthalate (DBP), which volumetrically absorbed ultraviolet (UV) laser light. Nonlinear absorption coefficients and laser breakdown thresholds were measured for pure water and UV optical materials intended to confine plasma. Test bench experiments were performed to produce standing acoustic waves as initial perturbations at the interface between two immiscible liquids.

In this paper, we present the results of studies on ion emission characteristics of a laser plasma produced from a copper nano-particle layer of 1–3 µm thickness coated over polished surface of a solid copper target. Laser intensity of 1013–1014 W/cm2 was produced on the targets by a 2 J Nd:glass laser having a variable pulse duration of 300–800 ps. Nano-particle size was in the range of 15–25 nm. Ion emission from the nano-particle plasma was compared with plasma generated from a polished copper target. Ion emission from the nano-structured target was observed to depend on the polarization of the incident laser beam. This effect was stronger for a shorter laser pulse. X-ray emission was measured in the soft and hard X-ray region (0.7 to 8 keV) using various X-ray filters. A nano-particle coated target is found to yield a larger flux as well as velocity of ions as compared to polished target when the laser polarization is parallel to the plane containing target normal and detector axis. However, no X-ray enhancement has been observed in the wavelength range 1.5 to 20 Å.

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 the symmetry of cylindrical implosions of laser targets with parameters corresponding to experiments proposed for the LIL laser facility at Bordeaux: eight laser beams in octahedrical configuration, delivering a total of 50 kJ of 0.35 µm laser light in 5 ns, impinging on 1.26 mm diameter polystyrene cylindrical shells filled with deuterium at 30 bar and 5.35 mg cm−3; this configuration allows to place diagnostics along the symmetry axis to evaluate directly the uniformity of implosion. Numerical studies have been carried out by using the hydrodynamic computer codes MULTI and CHIC, including one-dimensional, and two-dimensional R–Z and R–θ simulations. Deuterium is compressed into a 1 mm long and 50 µm diameter filament, with density ranging from 2 to 6 g cm−3 and temperatures above 1000 eV. In spite of the reduced numbers of beams, a good symmetry can be achieved with a careful choice of the irradiation pattern. The heat transport smoothing between laser absorption zone and ablation layer plays a fundamental role in the attenuation of residual non-uniformities. Also, it has been found that the radiation transport determines the radial structure of the compressed filament.

This paper presents a review of physical principles, design, and performances of plasma-cathode direct current (dc) electron beam guns operated in so called fore-vacuum pressure (1–15 Pa). That operation pressure range was not reached before for any kind of electron sources. A number of unique parameters of the e-beam were obtained, such as electron energy (up to 25 kV), dc beam current (up 0.5 A), and total beam power (up to 7 kW). For electron beam generation at these relatively high pressures, the following special features are important: high probability of electrical breakdown within the accelerating gap, a strong influence of back-streaming ions on both the emission electrode and the emitting plasma, generation of secondary plasma in the beam propagation region, and intense beam-plasma interactions that lead in turn to broadening of the beam energy spectrum and beam defocusing. Yet other unique peculiarities can occur for the case of ribbon electron beams, having to do with local maxima in the lateral beam current density distribution. The construction details of several plasma-cathode electron sources and some specific applications are also presented.

The aim of the reported research is to contribute to investigation of new processes and methods interlinking nuclear and laser-plasma physics. With respect to requirements of nuclear experiments at medium-size high-power lasers, the selection of proper candidates for studying the excitation and decay of low-lying nuclear states is reviewed. An experimental approach to the identification of low-energy nuclear transitions is discussed, simple estimates of the 181Ta excitation yield in the laser-generated plasma provide a theoretical basis for planning future work. First tests and results of the experiments at the laser facility PALS are presented.

The current capsule target design for the first ignition experiments at the NIF Facility beginning in 2009 will be a copper-doped beryllium capsule, roughly 2 mm in diameter with 160-µm walls. The capsule will have a 75-µm layer of solid deuterium-tritium on the inside surface, and the capsule will be powered by X-rays generated from a gold/uranium cocktail hohlraum. The design specifications are extremely rigorous, particularly with respect to interfaces, which must be very smooth to inhibit Rayleigh-Taylor instability growth. This paper outlines the current design, and focuses on the challenges and advances in capsule fabrication and characterization; hohlraum fabrication, and deuterium-tritium layering and characterization.

Proposed laser fusion power plant concepts suffer from the huge size and expense of the lasers needed for compression and ignition. In a 1969 study (classified in 1970 and declassified in 2007), the idea to use chemical high explosives for the pumping of megajoule lasers was explored. Apart from being less expensive by orders of magnitude, such lasers are expected to be much more compact, and with their large energy, output could simultaneously drive several thermonuclear micro-explosion chambers. Because of its topical importance, I accepted the journal's invitation to publish a previously classified work, but with new unpublished ideas, with the previously classified paper put into the appendix.

Laser produced ion beams have a large divergence angle and a wide energy spread. To our knowledge, this is the first demonstration of collimation and monochromatisation of laser accelerated proton beams, using a permanent quadrupole magnet lens system. It acts as a tunable band pass filter by collimating or focusing the protons with the same energy. Because it gathers nearly the whole proton emission, a strong enhancement of the beam density appears. For the collimated beam, an increase of the proton density in the (3.7 ± 0.3) MeV energy band up to a factor of ~30, from possible 40, relative to the non-collimated beam is demonstrated. With the help of this simple, reliable, and well established technique new perspectives will be opened for science and technology, monoenergetic ion beams can be attained in any lab, where a source of laser accelerated ions exist. This finding enables to apply afterward well known beam steering techniques to the formed ion beam, which are applied in conventional accelerators to manipulate the beam parameters or to transport the beams and make them use in many application.