The laser beat wave programs at Rutherford Appleton Laboratory and Ecole Polytechnique are reviewed. The techniques used to generate by multiphoton ionization the highly uniform plasmas needed for the beat wave are described. Evidence of the generation of a 2% plasma wave using laser beams at 1.064 and 1.053 μm is presented. The plasma wave suffers damping, possibly by the modulational instability. The use of a high-power short laser pulse for plasma-wave generation by the wake-field process is discussed. This process has the advantage that there is no resonance as in the beat wave, and since the plasma wave is generated on the time scale of the plasma period, instabilities are unlikely to be important.

First experimental results with a pulsed iodine photodissociation laser controlled by target plasma reflectivity are reported. One of the laser mirrors is substituted for a focusing lens and a solid tilted target is located in its focal region. The laser dynamics depends on the geometry of the set-up. Laser pulse durations from 200 to 5 ns were observed if the resonator length was changed from 2 to 5 meters. Simultaneous mode-locking and Q-switching took place if the resonators were longer than 3 meters. Peak power densities of up to 1011 W/cm2 on the target and about a 1 per cent plasma reflectivity, increasing with increasing power density, were measured. A theoretical explanation of the laser behaviour and a comparison of our observations with previous results obtained with TEA-CO2 and Nd-glass amplifiers are presented.

The emission of the third continuum of argon in the wavelength range between 175 and 250 nm and the vacuum ultraviolet emission of neon (λ < 100 nm) has been studied by timeresolved optical spectroscopy. The target gases at pressures between 2 and 100 kPa were excited with a pulsed beam of 100 MeV 32S9+ ions from the Munich Tandem van de Graaf accelerator. Wavelength spectra recorded in different time windows after the 2-ns beam pulses show that two different components contribute to the third continuum of argon. A radiative lifetime of 5.71 ± 0.08 ns for the Ar22+ molecule and a rate coefficient k3 = (1.46 ± 0.12) x 10-30 cm6/s for the reaction Ar2+ + 2Ar → Ar22+ + Ar were obtained from the pressure dependence of time spectra at a wavelength of 190 nm. From time- and pressure-dependent studies of the third continuum emission of neon at a wavelength of 99 nm, rate coefficients k2 = (3.6 ± 0.3) x 10-13 cm3/s for the bimolecular reaction Ne2+ + Ne→ 2Ne+ and k3 = (2.84 ± 0.09) X 10-31 cm6/s for the termolecular reaction Ne2+ + 2Ne → Ne22+ + Ne were determined.

The construction of the Terawatt Accumulator (TWAC) facility is nearly completed at the ITEP in Moscow. All the major milestones have been successfully passed with a beam of carbon ions, except for the final result (the high power beam accumulation), which is on the way. The beam of C4+ ions delivered by the laser ion source is accelerated up to the energy of 300 MeV/amu by two steps—in the linear injector I3 and in the booster synchrotron UK. The accelerated beam is extracted from the UK ring and transferred to the U10 accumulator ring. Non-Liouvillian stripping technique (C4+ ⇒ C6+) is applied for stacking of C6+ batches into the accumulator ring U10. First experiments with extracted beam of ions have started in 2002. Status of the TWAC components, current results of activities aiming at mastering the ion beam stacking technique, and outlook for the TWAC advance are presented.

The effects of high-Z dopant on the laser-driven ablative Richtmyer–Meshkov instability (RMI) are investigated by theoretical analysis and radiation hydrodynamics simulations. It is found that the oscillation amplitude of ablative RMI depends on the ablation velocity, the blow-off plasma velocity and the post-shock sound speed. Owing to enhancing the radiation at the plasma corona and increasing the radiation temperature at the ablation front, the high-Z dopant in plastic target can significantly increase the ablation velocity and the blow-off plasma velocity, leading to an increase in oscillation frequency and a reduction in oscillation amplitude of the ablative RMI. The high-Z dopant in plastic target is beneficial to reduce the seed of ablative Rayleigh–Taylor instability. These results are helpful for the design of direct drive inertial confinement fusion capsules.

Nonmonotonic plasma potential structures are a common feature of many double layers and sheaths. Steady state plasma potential wells separating regions having different plasma potentials are often found in laboratory experiments. In order to exist, such structures all must find a solution to a common problem. Ions created by charge exchange or ionization in the region of the potential well are electrostatically confined and tend to accumulate and fill up the potential well. The increase in positive charge should eliminate the well. Nevertheless, steady state structures are found in which the wells do not fill up. This means that it is important to take into account processes which ‘pump’ ions from the well. As examples of ion pumping of plasma wells, we consider potential dips in front of a positively biased electron collecting anode in a relatively cold, low density multidipole plasma. Pumping is provided by ion leaks from the edges of the potential dip or by oscillating the applied potential. In the former case the two dimensional character of the problem is shown to be important.

The electromagnetic field structures and transport properties of laser produced relativistic beam electrons propagating through Au+25, Cu+20, Al+10, and C+5 plasma foils are investigated. Simulations show that high plasma resistivity as well as high collision rate of the beam electrons with gold and copper plasmas can hinder the forward motion of the beam electrons inside the targets. However, the beam electrons can propagate for a relatively long distance in aluminum and carbon plasma targets. They are well collimated by the strong self-generated resistive magnetic field, resulting in higher sheath electric fields behind the target. The use of low-Z target material is therefore more efficient for collimating beam electrons as well as generating higher-energy ions.

We have compensated for gain saturation in the Nova amplifiers by producing shaped input optical pulses. A silicon switch device generates kilovolt electrical pulses for driving pockels cells. The pulse shape is easily controllable with subnanosecond resolution.

(This article appeared in Volume 23, Number 3, Pages 297–302, 2005)

A detailed study of Wakefield excitation in very dense quantum plasma is presented. Electric and magnetic Wakefields have been obtained for a particular profile of the laser pulse, using perturbative technique involving orders of the incident laser beam. The Wakefields can trap electrons and accelerate them to extremely high energies. It is observed that the quantum effects significantly change the classical nature of the Wakefield. The axial and radial forces acting on a test electron due to the Wakefields have been evaluated.

We present a diffusion approximation describing the flow of thermal radiation that preserves several important features of the underlying equation of radiative transfer. Specifically, this diffusion description: (1) is flux limited; (2) reduces to the correct transport weak gradient limit; (3) allows correct and simultaneous exponential growth and Decay for a certain class of problems; (4) gives correct transport results for certain contiguous half-space problems; and (5) allows the radiative flux and the gradient of the radiation energy density to point in independent directions. This treatment extends and generalizes earlier flux-limited diffusion approximations that are widely used in radiation–hydrodynamics calculations.

In the present paper, spatial amplitude modulation instability arising due to relativistic self-phase modulation and relativistic cross phase modulation of two co-propagating, linearly polarized laser beams (with arbitrary relative polarization) interacting with homogeneous plasma, has been studied. Wave equations including finite perturbation length effects, group velocity dispersion, and coupled nonlinear source term have been set up. Coupled dispersion relation for the two laser beams has been derived and solved numerically. The growth rate of modulation instability has been obtained and compared with the growth rate of a single beam propagating in homogeneous plasma. It has been shown that modulation instability of a single beam may either be enhanced or suppressed by co-propagation of another laser beam having appropriate polarization.

Kinetic modeling of laser-ion beam generation from the “break-out afterburner” (BOA) has been modeled for several deuteron-rich solid-density target foils. Modeling the transport of these beams in a beryllium converter shows as much as a fourfold increase in neutron yield over the present state of the art through the use of alternative target materials. Additionally, species-separation dynamics during the BOA can be exploited to control the hardness of the neutron spectra, of interest for, for example, enhancing penetrability in shielded material in active neutron interrogation settings.

The interaction of Xe (λ ∼ 1.73 μm) and XeCl (0.308 μm) laser radiation with surfaces of metal and TiN-ceramic coatings on glass and steel substrates has been studied. Correlation between parameters of surface erosion versus laser-specific energy was investigated. Monitoring of laser-induced erosion on smooth polished surfaces was performed using optical microscopy. The correlation has been revealed between characteristic zones of thin coatings damaged by irradiation and energy distribution over the laser beam cross section allowing evaluation of defects and adhesion of coatings. The interaction of pulsed periodical CO2 (λ ∼ 10.6 μm), and Xe (λ ∼ 1.73 μm) laser radiation with surfaces of teflon (polytetrafluoroethylene—PTFE) has been studied. Monitoring of erosion track on surfaces was performed through optical microscopy. It has been shown that at pulsed periodical CO2-radiation interaction with teflon the sputtering of polymer with formation of submicron-size particles occurs. Dependencies of particle sizes, form, and sputtering velocity on laser pulse duration and target temperature have been obtained.

Laser plasma experiments, which demonstrated the single order diffraction property of spectroscopic photon sieve (a novel single-order diffraction grating), were performed on the SILEX-I femto-second laser facility. High-intensity laser radiation was focused onto a Cu target to generate plasma. The spectra of soft X-ray from copper plasmas have been measured with spectroscopic photon sieve based spectrograph. The results show that the spectroscopic photon sieve is able to provide soft X-ray spectrum free from higher-order diffraction components. The measured spectra obtained with such a spectroscopic photon sieve need no unfolding process to extract higher-order diffraction interference.

A flyer with high velocity and good integrity can be obtained by laser driven multi-layered film. In order to deeply study the action mechanism, a calculation model of laser driven multi-layered flyer has been established, taking into account the effect of multi-layered on flyer velocity increase. Multi-layered flyer velocity driven by laser pulse beam has been calculated to decide film configuration capable of forming a high velocity flyer. Taking this film configuration as object, an intense laser driven multi-layered flyer experiment has been conducted to obtain flyer velocity and verify calculation model. In order to analyze flyer motion details, a two-dimensional axisymmetric computation model of laser driven flyer has been established. In this study, laser energy spatial-temporal distribution, film ablation, and plasma absorption laser to drive flyer have been considered. Saha ionization equilibrium equation is adopted to calculate film ionization degree and give plasma state equation. Dynamic mesh algorithm is used to calculate flyer motion. Coupled numerical simulation of laser ablation, laser interaction with plasma and plasma driven flyer has been achieved. Results show that flyer velocity firstly increases and then decreases with the increase of ablation layer thickness. Ablation layer has an optical laser absorption depth for different layer materials. Plasma velocity distribution is linear in axial when flyer accelerates. Insulation layer can decrease flyer temperature effectively to keep flyer integrity.

We apply an Eulerian Vlasov code to study the amplification of an ultra-short seed pulse via stimulated Raman and Brillouin backscattering of energy from a long pump pulse, assumed at constant amplitude, in a plasma embedded in an external magnetic field. Detailed analysis of the spectra developed during the amplification process are presented, together with the evolution showing the pump depletion, accompanied by the counter-propagating seed-pulse amplification, compression and increased steepness of the waveform. In addition to the problem of the amplification of ultra-short seed pulses, there is an obvious academic interest in the study of problems of amplification of electromagnetic waves observed in many situations in laboratory plasmas and in the magnetosphere and other geophysical situations, such as in the environments of planets, where important variations in the presence and strength of magnetic fields are observed. The numerical code solves a one-dimensional relativistic Vlasov–Maxwell set of equations for a plasma in a magnetic field for both electrons and ions. We also apply the code to the problem of wakefield acceleration. The absence of noise in the Eulerian Vlasov code allows one to follow the evolution of the system with an accurate representation of the phase-space structures of the distribution functions.

High inductive helical support provides a solution to controlling the alignment error of inner electrodes in magnetically insulated transmission lines (MITLs). Three-dimensional particle-in-cell simulations were performed to examine the current loss mechanism and the effects of structural parameters on electron flow in an MITL with a helical inductor. An empirical expression related to the ratio of electron current loss to anode current and the ratio of anode current to self-limited current was obtained. Electron current loss caused by helical inductor with different structures was displayed. The results indicate that the current loss in an MITL, near an inductive helical support, comprises both the inductor current and the electron current loss. The non-uniform structure and current of a helical inductor cause an abrupt change in the magnetic field near the helical support, which leads to anomalous behavior and current loss of electron flow. In addition, current loss in the inductive helical-supported MITL is negligible when the inductance of the support is sufficiently high. This work facilitates the estimation of electron current loss caused by the inductive helical support in MITLs.

This paper presents two-dimensional numerical simulations of heating of matter with intense heavy ion beams. It has been shown that it is very advantageous to irradiate the target with two different beams simultaneously, a main high intensity bunched beam of a heavy element like uranium and an unbunched low intensity beam of a lighter element like argon. The main beam is used to heat the target while the second beam is used as a diagnostic tool.

Influence of the shape of the focal spot on compression and heating of matter has also been studied using an elliptic focal spot with an ellipticity of 1.5 (semimajor axis is along y-axis and is 1.5 times the semiminor axis which is along x-axis). It has been found that the temporal behavior of the development of density, pressure, and temperature profiles along different directions is quite different, which is not the case with a circular focal spot.

Laser pulses are focused in the interior of a human eye in areas of opacity to produce there an optical breakdown resulting in a high-temperature plasma, after which the filling up with liquid results in a transparent area. The empirically given limits for Q-switch laser pulses in the nanosecond range and for mode-locked pulses in the picosecond range are analyzed, and it is shown that these limits are below the self-focusing condition of laser beams in plasmas. A further analysis evaluates theoretically where the maximum limits are given in order to provide the parameters for the highest possible pulse energy that avoids damage in the eye by self-focusing.