The irradiation of solids with high energy laser or particle beams has led to a deeper understanding of the relaxation processes inside the target material. However, a lot of open questions remain. In the present paper, we will examine the irradiation of the model system Xe23+ @ 93 MeV → SrTiO3 within the framework of the two-temperature-model and study the electron-phonon-coupling g and the electron diffusivity De as well as the lattice diffusivity Dp. These are crucial parameters for which no experimental data is available. Experimentally, g is very difficult to measure and therefore theoretical predictions are of great importance. With the approach presented here it is possible to determine the coupling-constant by one order of magnitude.

The paper is devoted to the study of plasma effects, which are present in laser ablation at relatively high intensity (I ≥ 1012 W/cm2). We start from the classical “two temperature model” of laser ablation (“cold solid approximation”) and we extend it to higher intensities where laser-induced heating and laser-induced changes in the background material become relevant. The new model is also compared to experimental results on laser ablation of solid targets from short pulse lasers at high intensities (up to 1014 W/cm2). Finally, we consider the effects on laser-ablation of laser-generated fast electrons.

The present study deals with the propagation of short laser pulses in a parabolic plasma channel. A variational technique is used to obtain simultaneous evolution equations describing the laser pulse length and spot size in the presence of relativistic and ponderomotive nonlinearities. The effect of wakefields (inside the pulse) on the propagation characteristics of the laser beam is studied. Numerical methods are used to graphically analyze the evolution of the laser pulse length and intensity.

We report on the investigation of strong radiative shocks generated with the high energy, sub-nanosecond iodine laser at PALS. These shock waves are characterized by a developed radiative precursor and their dynamics is analyzed over long time scales (~50 ns), approaching a quasi-stationary limit. We present the first preliminary results on the rear side XUV spectroscopy. These studies are relevant to the understanding of the spectroscopic signatures of accretion shocks in Classical T Tauri Stars.

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.

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.

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.

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.

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.

Relativistic self distortion of a Gaussian laser pulse in inhomogeneous plasma in one dimension is investigated. The relativistic mass effect causes different portions of the pulse to travel with different group velocities leading to the steepening of the pulse front and broadening of the rear. This asymmetry created in the pulse shape gives rise to stronger ponderomotive force on electrons at the front and weaker at the rear. The fast moving electrons under this force are shown to have very significant net energy gain. The energy gain increases with the density scale-length and then saturates.

Dielectric functions of an electron plasma are calculated for an electron gas in which number, momentum, and energy are conserved during electron-electron collisions. They are compared with others in the literature, revealing that, in general, that imposition of the conservation laws tends to make the full conserving dielectric response more similar to the random phase approximation dielectric response than without it. This is due to the fact that in the random phase approximation model all the conservation laws are also enforced. Our model is checked for other plasma degeneracies; concretely we consider partially degenerate plasmas and classical plasmas. The behaviour of the dielectric functions of these plasmas is similar to the degenerate one. Differences among dielectric functions are more significant than for the degenerate case, but it is mainly due to low relaxation time values. The most relevant issue for these plasmas is the fact that the consideration of energy conservation in the dielectric function is more important in these cases, because plasma temperature is significant.

The short D-D distance of 2.3 pm in the condensed material ultra-dense deuterium means that it is possible that only a small disturbance is required to give D+D fusion. This disturbance could be an intense laser pulse. The high excess kinetic energy of several hundred eV given to the deuterons by laser induced Coulomb explosions in the material increases the probability of spontaneous fusion without the need for a high plasma temperature. The temperature calculated from the normal kinetic energy of the deuterons of 630 eV from the Coulomb explosions is 7 MK, maybe a factor of 10 lower than required for ignition. We now report on experiments where several types of high-energy particles from laser impact on ultra-dense deuterium are detected by plastic scintillators. Fast particles with energy up to 2 MeV are detected at a time-of-flight as short as 60 ns, while neutrons are detected at 50 ns time-of-flight after passage through a steel plate. A strong signal peaking at 22.6 keV u−1 is interpreted as due to mainly T retarded by collisions with H atoms in the surrounding cloud of dense atomic hydrogen.

Collimated proton beams from laser interaction with a slab having a hole on its backside are investigated using particle-in-cell simulation. The hot target electrons driven by the laser expand rapidly into the hole. However, at the hole's corners the electrons are strongly compressed and an intense electron jet is emitted from each corner, tightly followed by the ions. The plasma jets focus and collimate along the axis of the hole and can propagate without divergence within the hole. The effect of the hole diameter on the collimated proton beam is considered.

An infrared laser propagating through a semiconductor waveguide, embedded with a density ripple of wave number q, resonantly excites third harmonic radiation. The phase matching is achieved when q equals difference between third harmonic wave number and three times the wave number of the laser. The excited third harmonic is in higher order radial Eigen mode than the pump laser. The third harmonic efficiency increases with electron concentration and decreases with the frequency of the laser.

In this article, we investigate the effects of foam target composition and laser parameters on deuterium ion energy spectra with particle-in-cell simulations. We find that localized electrostatic fields with multi peaks around the surfaces of lamellar layers inside foam target are induced. These fields accelerate deuterium ions from thin foam layers by restricting the flow of hot electrons. This mechanism of ion acceleration called as bulk ion acceleration generates large number of high energy deuterium ions. Deuterons inside foam target are accelerated up to 126 MeV in case of oblique optimal angle of 30° where it is much greater than the normal laser incidence energy of 88 MeV.

This paper presents an investigation of the focusing of Hermite-cosh-Gaussian laser beams in magneto-plasma by considering ponderomotive nonlinearity. The dynamics of the combined effects of nonlinearity and spatial diffraction is presented. To highlight the nature of focusing, plot of beam-width parameter vs. dimensionless distance of propagation has been obtained. The effect of mode index and decentered parameter on the self-focusing of the beams has been discussed.

In this paper, the ion jet generation from the interaction of an ultraintense laser pulse and a rear-side concave target is investigated analytically using a simple fluid model. We find that the ion expanding surface at the rear-side is distorted due to a strong charge-separation field, and that this distortion becomes dramatic with a singular cusp shown on the central axis at a critical time. The variation of the transverse ion velocity and the relative ion density diverge on the cusp, signaling the emergence of an on-axis ion jet. We have obtained analytical expressions for the critical time and the maximum velocity of the ion jet, and suggested an optimum shape for generating a collimated energetic ion jet. The above theoretical analysis has been verified by particle-in-cell (PIC) numerical simulations.