Generation of large amplitude plasma waves using high-power lasers in either the wakefield or beat-wave scheme is considered. We show how the nonlinear behavior of the plasma wave may make it advantageous to split the total energy into more than one pulse in the wavefield scheme. When a beat wave is generated by a pulse of finite length, we show how the final wave amplitude may be enhanced if the frequency of one or both pulses is chirped in such a way that the wavelength of the beat increases from the front to the back of the pulse.

The time-dependent soft X-ray emission of helium and nitrogen plasmas generated by optical-field ionization is reported. The experiments were carried out by focusing pulses of the high-power Ti:sapphire laser of the Lund Institute of Technology (λ = 796 nm, pulse duration 150 fs, pulse energy 150 mJ) to a 50-μm diameter spot close to a nozzle, using He and N2 as target gases. The emission on He+, N4+, and N3+ resonance lines was recorded by means of a flat-field grating spectrometer coupled to an X-ray streak camera. A pronounced difference in the temporal shape of the emission of the Lyman-α line of hydrogen-like helium and of the 2p−3d resonance lines of lithium-like and beryllium-like nitrogen was observed. The helium line exhibited an initial spike followed by a slow revival of the emission, whereas the nitrogen lines showed a slow decay after a fast initial rise. These observations are explained with the help of simulations.

Far-field images produced using different random phase plates on a pulsed laser beam focused with variousf/numbers were recorded by a charge-coupled device (CCD) camera and then analyzed. Envelope spot sizes agree with diffraction theory while mean sizes of the pattern structures have been found to be larger than the diffraction limit. The probability density distribution of intensity in the focal plane is not the expected exponential. A central symmetry of the pattern has also been seen after suitably aperturing the beam. Some consequences for the use of powerful RPP-treated laser beams in laser-plasma interactions are discussed.

The plasma produced during pulsed-laser deposition of thin carbon films is studied in the presence of ambient gases (Air, He, Ar) at low and moderate irradiances of Nd:YAG laser. The presence of ambient gas shows a pronounced effect on the dynamics of the plasma plume. At moderate intensity, we report an appearance of a peculiar double-peak structure in the temporal profile of the C II transition in laser-produced carbon plasma as it expands into a background gas. We believe that the structure originates mainly due to stratification of the plasma into fast and slow ion components at the interface where Rayleigh-Taylor instability occurs. Thin carbon films deposited on silicon in the presence of argon gas have shown the characteristic features of diamond-like carbon in X-ray diffraction and Raman Spectroscopy. The X-ray diffraction pattern of carbon film deposited at 1 torr of argon gas pressure shows the dominance of (111), (220), (311), and (400) crystalline plane of cubic diamond.

An experimental investigation on X-ray emission from laser-produced plasmas is presented and the properties of such an emission of interest for application purposes are examined. Plasmas were generated by focusing 1 μm, 3 ns Nd laser pulses onto Al and Cu targets at an intensity of 1013 W/cm2. The temporal evolution of the emission and its spectral features were investigated by using an X-ray streak-camera and an X-ray photodiode. In the case of Cu targets, the analysis of the emission showed two spectral components. The main component was centered at ≈ 1.2 keV and a minor component, whose intensity was measured to be 10-3 of the previous component, was observed at ≈7 keV. The X-ray conversion efficiency, in the investigated spectral region, was measured to be 1% for Cu targets and 0.3% for Al targets.

A vertical dispersion variant of the Johann spectrometer has been used to record the highresolution X-ray spectra of the chlorine He-like resonance line group emitted from lowradiance plasma. The emission profiles were measured at two observation angles and decomposed into single spectral lines by using a fit based on the Levenberg-Marquardt algorithm. The results of computerized analysis of the one-dimensional (1-D) spatially resolved spectra were used to evaluate the distribution of the main plasma parameters. The electron temperature gradient 7.5·104 eV cm-1 was computed by modeling the measured spectra with the collisional-radiative package RATION. The blowoff maximum velocities 4.2–6.1·107 cm s-1 and the velocity gradients 0.9–1.6·109 s-1 were determined from the Doppler shifts of individual spectral lines within their different spatial extent.

In this paper we present measurements of energy transport in hot, high-density plasmas produced by picosecond laser interaction with solid targets. The propagation of the ablative heat wave was studied by using X-ray-ultraviolet (XUV) spectroscopy with picosecond temporal resolution. Measurements show that for laser intensities on target above 1016 W/cm2, strong inhibition of heat flux toward the cold target occurs. A detailed modelling of the experimental data is presented in which heat transport and absorption processes are taken into account self-consistently. Finally the role played by lateral transport and self-induced magnetic fields in our experiment is also discussed.

Stimulated Raman scattering driven by intense subpicosecond laser drivers is analyzed, in particular, the effects of the pulse shape and relativity on the instability and its characteristic spectra. The analysis is carried out in the pulse group velocity frame (Lorentz transformed) where growth rates for backscattering are decreased relative to their values when analyzed in the laboratory frame, while forward-scattered growth rates have greatly enhanced values. A range of intensities and densities is considered, appropriate to recent experiments, which ranges from strongly coupled scattering at high densities (even for forwardscattering) to stimulated Compton scattering regimes for backscattering and relativistically trapped forwardscattering at low densities. The inhomogeneities in intensity and density cause mode conversion between waves inside and outside the pulse. This can be at a modest level, as for backscattering, or extreme as in the case of forwardscattering when the Raman scattered light can be trapped within the laser pulse. The consequent feedback between modes within the pulse allows solutions, absolutely growing in the pulse frame, to be found.

The physics of the formation of cryogenic fuel layers with various internal structures has been studied in regard to the development of promising layering techniques for modern inertial confinement fusion (ICF) experiments. The investigations have been made with inertial confinement fusion target (ICF targets) and in a target modeling system (TMS) with the nonisochoric process of cryogenic layer formation. The results indicate that the solidlayer structure in TMS differs essentially from that obtained in ICF targets. The thermal history of a fuel layer at separation into the condensed and vapor phases is found to depend upon whether the initial gas density is more, less, or equal to the critical value for a given fuel material. The issue on the fuel-layer fabrication in the form of a long-living quasiamorphous layer is considered. A new low-temperature method to homogenize a polycrystalline cryogenic layer has been proposed and examined. The operational temperature was 4.2 K. The time to achieve the complete homogeneity of solid hydrogen was 150 s. No limitation, with respect to the thickness of a cryogenic layer, was found. The critical target is suggested as a new type of an ICF target.

A steady-state analysis of Gaussian laser beam in a nonlinear medium has been presented. It is shown that an oscillatory self-guided beam (whose width is oscillating with the propagation distance) in a saturable nonlinear medium can be uptapered by material gain. Moreover, the present investigation suggests that under certain conditions it is possible to obtain a stationary self-guided beam (planar wavefront) in a nonabsorbing medium from an initially oscillatory (nonplanar wavefront) beam in a nonabsorbing medium by uptapering it in a gain medium.