The coupled propagation of two electromagnetic waves in plasma is studied to establish the conditions for induced transparency. Induced transparency refers to the situation where both waves propagate unattenuated, although the frequency of one (or both) of them is below the plasma frequency so that it could not propagate in the absence of the other. The effect is due to the interaction of the waves through their beat, which modulates both the electron mass and, by exciting longitudinal plasma oscillations, their number density, and thus the plasma frequency. Starting from a relativistic fluid description, a dispersion relation for plane waves of weakly relativistic intensities is derived, which takes into account the polarization of the waves and the nonlinearities with respect to both their amplitudes. This serves as a basis for the exploration of the conditions for induced transparency and the modes of propagation.

The propagation of a 1-ps laser pulse at intensities exceeding 1019 Wcm−2 in a low-density plasma channel was experimentally tested. The channel was produced by a lower intensity preceding pulse of the same duration. Plasma electrons were accelerated during the propagation of the main pulse, and high energy γ-ray detectors were used to detect their bremsstrahlung emission. The γ-ray yield was studied for different channel conditions, by varying the delay between the channel forming pulse and the high intensity pulse. These results are correlated with the interferograms of the propagation region into the plasma.

Utilizing an ultraintense (1016 W cm−2) fs laser, the laser/matter interaction of the tetrahedral CH3I molecule is investigated. A mass spectrum and the angular distributions of fragment ions arising from Coulomb explosion of molecular ions, obtained with linearly polarized light, are presented. The distributions for In+ (n ≤ 7), CHm+ (m ≤ 3), Cp+ (p ≤ 4) and H+ ions are all anisotropic and maximal when the polarization lies along the spectrometer axis. The molecule hence seems to behave as a diatomic, with the fragment ions being ejected along the field direction. Also presented are mass spectra of the isomers 1- and 2-nitropropane, which are explosive species, taken for horizontal and vertical polarizations at both 375 and 750 nm. It is shown that femtosecond laser mass spectrometry (FLMS) can be used to distinguish between these two isomers through their differing dissociation patterns. Isomer identification is important for many different applications and FLMS may provide a means of achieving this for a wide range of molecules.

In this work, the interaction of a transversely excited atmospheric (TEA) CO2 laser with tungsten–titanium (W-Ti) alloy deposited on austenitic stainless steel is considered. The W-Ti alloy as a refractory material possesses very good physicochemical characteristics such as thermochemical stability and high melting temperature. Studying of interactions of different energetic particles or laser beams with W-Ti coatings has both application and fundamental importance.

The morphological features of the W-Ti coating, deposited on austenitic stainless steel AISI 316, induced by a TEA CO2 laser after multipulse cumulative laser action, have been considered. The laser pulses with tail (FWHM = 120 ns, tail = 2 μs) and free-tail pulses (FWHM = 80 ns) have been employed. Laser pulses used in the experiment had equal peak power density I = 120 MWcm−2. For the given peak power density, excessive surface changes on the coating were registered. From direct observation on a microscopic scale (OM, SEM), it can be concluded that W-Ti coatings show different behavior under laser irradiation with various temporal pulse shapes.

We report on the design and characterization of a grazing-incidence flat-field spectrograph that allows simultaneously the measurement of spectrum, beam divergence, and absolute flux of EUV and soft X-ray radiation for a beam of high-order laser harmonics generated by the interaction between an ultrashort femtosecond laser pulse and a gas jet. The instrument seems a very powerful tool for the understanding of the generation process.

Analytical interest in nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) is related to their high mutagenicity and potential presence in a variety of environmental media such as diesel exhaust and urban air particulate matter. Furthermore, fundamental interest in these molecular systems stems from the photophysics of the labile NO2 functional group, which has been investigated using mass spectrometry. The nitro-PAHs, 1-nitronaphthalene, 9-nitroanthracene, and 1-nitropyrene, have been studied using both femtosecond (λ = 395 and 790 nm) and nanosecond (λ = 266 nm) lasers coupled to a reflectron time of flight mass spectrometer. Analysis of mass spectra taken over a range of intensities (1014–1015 W/cm2) has demonstrated that structurally specific ions can be observed for each molecule, with little or no fragmentation at lower intensities. It has also been found that an intact parent ion can be detected using femtosecond ionization at 395 nm in each case. This work demonstrates the potential use of laser desorption/femtosecond laser mass spectrometry (LD/FLMS) as an analytical technique for the detection of nitro-PAHs and other environmental pollutants and as a means of studying the photodynamics of labile molecular systems.

We report on the observation of neutrons resulting from a thermonuclear reaction D + D = 3He(0.82 MeV) + n(2.45 MeV), taking place in plasma created on the surface of a modified solid-state target. The plasma was produced by a 200-fs laser pulse with intensity in excess of 1016 W/cm2 and energy of only 0.3 mJ.

A method of creating all-optical devices for logic information processing is presented. The mechanism is based on virtual photon interaction in quantum field description, or dipole moment interaction in classical description. The device consists of two optical information bits channels and one optical bits channel of logic commands like AND, NOT, OR. A variety of logic operations can be achieved on one optical setup by polarization change of the logic bits which determines the logic commands. I present another application for the method as an information channels selector.

The wakefield acceleration driven by a single laser pulse in a narrow plasma-filled solid waveguide is considered. Parameters of the waveguide which provide the maximum energy gain of accelerated particles at a given length and peak power of the driver are found in the approximation of a relativistically weak driver. The obtained formulas are illustrated by calculating the electron energy gain achievable with the terawatt laser of Utsunomiya University.

Brillouin backscattering instability is investigated in inhomogeneous collisional plasma. The slow-coupling equations for the instability in a medium with linear density ramp are obtained. For large inhomogeneity scale length, the homogeneous growth rate is found to be modified by a factor of

[1/square root(2) times square root(ω02/ (ω02 + νe2) + ω0/square root(ω02 + νe2))]

For the convective instability, the amplification factor is found to be

[Λ = (|γB0|2/2β)(ω02/ω02 + νe2)]

The presence of collisions leads to a reduction in both the growth rate and the amplification factor, where the threshold intensity for the instability to occur increases.

We present the design of a single-shot third-order autocorrelator that can be used to measure optical pulse lengths of ultrashort pulses within a fixed time window on a single-shot basis. It has a number of advantages over traditional second-order autocorrelation devices, namely a more direct and accurate measurement of pulse shape, the ability to differentiate temporal activity ahead and behind the pulse, and an increased dynamic range. The design is linear and is, in principle, no more difficult to construct and operate than a second-order autocorrelator.

We report on a new technique that we used to accurately time the velocity of a cluster beam. It involves deflecting particles away from their usual beam path by scattering with an ablation plume. We were able to time the occurrence of a C60 cluster beam to better than 0.2%. This technique was critical in recent light-force polarizabilities experiments.

X-ray emission spectra in the 5–22 nm range were recorded from planar and structured (meshlike groove surface) gold targets at 45° and 90° to the laser axis. A laser beam of 10-ns duration with EL ≤ 700 mJ and 1.06-μm wavelength was used for the experiment. Experimental results indicate an enhanced X-ray yield from a structured target as compared to a planar target under identical experimental conditions. Increased X-ray emission is attributed to plasma confinement and the possibility of conversion of kinetic energy into localized thermal energy of the plasma. Results are analyzed explicitly on the incident laser energy.

Charged transparent macroparticles of silicium carbide of radius r = 0.5 μm are submitted to the repeated radiation pressure of a laser beam which follows the sides of a square 3.5 × 3.5 m, using total reflection on three prisms. The macroparticles follow a closed path since they are deflected by a strong electric field, using magnetic insulation. After 4650 revolutions, velocities up to 106 km/s can be reached.

A study of angular distribution of X-ray line radiation emitted from a laser-produced plasma is presented. Plasma was produced by irradiating a planar magnesium target using single laser pulses of 6 J, 4.5 ns (FWHM) from an Nd:glass laser system. Angular distribution of X-ray emission in the spectral range of 7–10 Å was recorded using a single X-ray crystal spectrograph. X-ray emission intensity for different resonance lines is observed to decrease up to an angle of ∼45° with respect to target normal, followed by a significant increase at higher angles. The observed departure of angular distribution from a monotonically decreasing behavior is broadly in agreement with the calculations of the escape factor of the radiation at different angles from a thick disk-shaped plasma using a spectroscopic code RATION.

In this article, we study the effect of various parameters on the estimation of radiation temperature inside an indirect drive ICF hohlraum and also study the hydrodynamics of aluminum and gold foils driven by the hohlraum radiation. A multigroup one-dimensional, radiation hydrodynamic code is used for this study. Opacities are calculated using a screened hydrogenic average atom model. We also investigate the opacities of Au-Sm and Au-Gd mixtures. It is shown that the mixing of two high Z materials can lead to an enhancement in the Rosseland means, which is of direct interest in indirect-drive inertial confinement fusion. The radiation temperature inside a cylindrical hohlraum is seen to be strongly dependent on the number of frequency groups used. One group radiation transport underpredicts the radiation temperature. It is shown that erroneous results can be obtained if the space mesh in the hohlraum wall is not fine enough. The spectrum of the radiation inside the hohlraum is seen to be different from Planck, especially in the high-energy range. This may lead to preheating of the target. Hydrodynamics of an aluminum foil driven by the hohlraum radiation is also presented in this article. A scaling law for the radiation-driven shock-wave speed in the gold foil is obtained.

Effects of an implosion nonuniformity with [ell ] = 1 ([ell ]: Legendre polynomial mode number) on the hot spark formation were investigated in a series of direct-drive implosion experiments at the Gekko-Xll glass laser (Yamanaka et al., 1987). The implosion dynamics and the performance from the early to final stage of the implosion were observed with a variety of X-ray imaging and neutron diagnostics. A drive nonuniformity in the implosion with [ell ] = 1 was observed in the shape of the accelerated target at the early stage of the implosion. At the final stage of the implosion, the resultant nonuniformity with [ell ] = 1 was also observed as a geometrical shift of core plasmas from the center of the chamber. The observed neutron yield and X-ray emission properties at the final stage of the implosion were significantly degraded with an increase of the implosion nonuniformity with [ell ] = 1. The experimental results were compared with one-dimensional (1-D) and two-dimensional (2-D) hydrodynamic simulations. As a result, it was found that the implosion nonuniformity with [ell ] = 1 shifts the whole implosion dynamics towards its direction and prevents the confinement of the gas fuel considerably. However, the experimentally observed degradation in the hot spark formation, such as reductions in neutron yield and features in X-ray emission, can be reproduced in 2-D simulations not with an asymmetric perturbation of [ell ] = 1 only but with multimode nonuniformities such as [ell ] = 1 coupled with some additional middle-mode ones (e.g., [ell ] = 6). Such a complex spike structure caused by the multimode nonuniformities was found to be essential for the experimentally observed rapid cooling of the hot spark.

The shadow monochromatic backlighting (SMB) scheme, a modification of the well-known soft X-ray monochromatic backlighting scheme, is proposed. It is based on a spherical crystal as the dispersive element and extends the traditional scheme by allowing one to work with a wide range of Bragg angles and thus in a wide spectral range. The advantages of the new scheme are demonstrated experimentally and supported numerically by ray-tracing simulations. In the experiments, the X-ray backlighter source is a laser-produced plasma, created by the interaction of an ultrashort pulse, Ti:Sapphire laser (120 fs, 3–5 mJ, 1016 W/cm2 on target) or a short wavelength XeCl laser (10 ns, 1–2 J, 1013 W/cm2 on target) with various solid targets (Dy, Ni + Cr, BaF2). In both experiments, the X-ray sources are well localized spatially (∼20 μm) and are spectrally tunable in a relatively wide wavelength range (λ = 8–15 Å). High quality monochromatic (δλ/λ ∼ 10−5–10−3) images with high spatial resolution (up to ∼4 μm) over a large field of view (a few square millimeters) were obtained. Utilization of spherically bent crystals to obtain high-resolution, large field, monochromatic images in a wide range of Bragg angles (35° < Θ < 90°) is demonstrated for the first time.

This paper reports some of the studies on nonconventional ICF approaches performed at the ICF Physics and Technology Laboratory of the AEEF in Frascati, Italy. Having as reference potential difficulties associated to the conventional central spark ignition (fuel mixing) and to the usual approach to fast ignition by laser (transfer and coupling of the energy pulse, fast electrons energy tuning), we have made explorative work on possible alternatives. The performances of targets ignited near stagnation by pulses of heavy ion beams (HIB) or by macroparticle impact were previously studied. The needed driver energy, the power, and the beam quality requirements, as well as the level of synchronization the implosion and the igniting pulse have been found. More recently, to relax some requirements on the HIB beam parameters set by the previous approach, the injected entropy approach (IE) has been introduced. In this method, the conditions for spark formation are set in the final stages of the implosion, when the spark fuel size is a few times the final size at stagnation (volume a few tens of the final). Energy is injected at this time to set the spark fuel on a high adiabat. In this paper, for illustration and comparison purposes, some relevant results we previously obtained for near-stagnation ignition are first introduced and critically reviewed. The new IE method, after a short analytical introduction, is presented and illustrated by the results of extensive 2-D numerical simulations. The considered cases refer to imploding cylinders of finite length. As required by this approach, one or two opposing beams axially injected additional energy, whereas the acceleration stage of the cylindrical low-entropy implosion was assumed driven by a different driver. Heavy ion beams, soft X-rays (SXR), and laser generated light ion beams were considered as vectors for the entropy injection. Issues related to the feasibility of these generators are discussed. The study was made for various initial conditions leading to different ignition modes and burn propagation. The most recent results on the injected entropy method to the ignition of high gain targets are included.

Medium-mass ion beams including nitrogen and oxygen were produced from a cryogenic diode with N2O ice as the ion source. The nominal diode voltage was 300–400 kV, and the peak ion current was 240 A. The beam divergence angle was measured with a five-aperture time-integrated pinhole camera. The five camera images were analyzed to estimate the spatial distribution of the beam source divergence angle along the anode radius, yielding a value of 5–6 mrad for the average microdivergence. This is low enough for this ion source to be studied further in the near future. If possible, we want to consider this as one of the probable candidate ion sources for ion beam drivers for future inertial confinement fusion (ICF) and inertial fusion energy (IFE) applications.