Spatiotemporal evolution of high-power relativistic laser pulses in electron-positron-ion plasmas

The spatiotemporal pulse dynamics of a high-power relativistic laser pulse interacting with an electron-positron-ion plasmas is investigated theoretically and numerically. The occurrence of pulse compression is studied. The dependence of the mechanism on the concentration of the background ions in electron positron plasma is emphasized.

Creation of persistent, straight, 2 mm long laser driven channels in underdense plasmas

The experimental study of the behavior of deuterium plasma with densities between 2 X 1018 and 2 x 10(20) cm(-3), subjected to a 6 TW, 30 ps, 3 X 10(18) W cm(-2) laser pulse, is presented Conclusive experimental proof that a single straight channel is generated when the laser pulse interacts with the lowest densities is provided This channel shows no small-scale longitudinal density modulations, extends up to 2 mm in length and persists for up to 150 ps after the peak of the interaction Bifurcation of the channel after 1 mm propagation distance is observed for the first time For higher density interactions, above the relativistic self-focusing threshold, bubblelike structures are observed to form at late times These observations have implications for both laser wakefield accelerators and fast ignition inertial fusion studies (C) 2010 American Institute of Physics [doi 10 1063/1 3505305]

Spatially Resolved Measurements of Laser Filamentation in Long Scale Length Underdense Plasmas with and without Beam Smoothing

The onset of filamentation, following the interaction of a relatively long (tau(L) similar or equal to 1 ns) and intense (I-L similar or equal to 5 x 10(14) W/cm(2)) laser pulse with a neopentane filled gas bag target, has been experimentally studied via the proton radiography technique, in conditions of direct relevance to the indirect drive inertial confinement fusion scheme. The density gradients associated with filamentation onset have been spatially resolved yielding direct and unambiguous evidence of filament formation and quantitative information about the filamentation mechanism in agreement with previous theoretical modelings. Experimental data confirm that, once spatially smoothed laser beams are used, filamentation is not a relevant phenomenon during the heating laser beams propagation through typical hohlraum gas fills.

Application of a picosecond laser plasma continuum light source to a dual-laser plasma photoabsorption experiment

The characteristics of an extreme-ultraviolet (XUV) continuum light source and its application to a dual-laser plasma (DLP) photoabsorption experiment are described. The continuum emitting plasma was formed by focusing a 7 ps, 248 nm, 15 mJ laser pulse onto a number of selected targets known to be good XUV continuum emitters (Sm, W, Au and Pb), while the second absorbing plasma was produced by a 15 ns, 1064 nm, 300 mi pulse. The duration of the continuum emission for these plasmas has a mean value of similar to 150 ps, but depends on both the target material and the picosecond laser pulse energy. Using this picosecond DLP set-up we have been able to measure the photoabsorption spectrum of an actinide ion (thorium) for the first time.

Spectroscopic characterization of prepulsed x-ray laser plasmas

Through the use of time-integrated space-resolved keV spectroscopy, we investigate line plasmas showing gain in Ne-like nickel, copper, and zinc for irradiation using the prepulse technique. The experiments were conducted at 1.06 mu m with the prepulse to main pulse intensity contrast ranging from 10(-6) to 10(-2). The effect of the prepulses on the plasma conditions is inferred through spectroscopic line ratio diagnostics for the electron temperature, the Ne-like ground-state density, and the lateral size of the Ne-like region. It is observed that neither the value of the electronic temperature nor its spatially resolved profile along the linear focus axis varies significantly with the prepulse level, contrary to the lateral width and the density of the Ne-like region in the plasma, which are seen to increase. These results explain, at least in part, why prepulsed x-ray lasers show such high gain and brightness.

EFFECT OF WEAK PREPULSES ON COLLISIONAL X-RAY LASER PLASMAS

Through the use of time-integrated space-resolved keV spectroscopy, we characterize line plasmas showing gain in Ne-like Zn with prepulsed irradiation to explain the enhanced performances of x-ray lasers using the prepulse technique. It is observed that the value of the electron temperature does not vary significantly with prepulse level, nor does its spatially resolved profile along the line. The lateral width and density of the Ne-like region in the plasma are seen to increase with the prepulse level. (C) 1995 Optical Society of America

THE EXPANSION HISTORY OF ALUMINUM TARGETS RELEVANT TO X-RAY LASER SCHEMES

For the first time, the technique of point projection absorption spectroscopy - which uses an intense, point source of X-rays to project and spectrally disperse an image of a plasma onto a detector- has been shown to be applicable to the study of expanding aluminium plasmas generated by approximately 80ps (2-omega) laser pulses. Massive, stripe targets of approximately 125-mu-m width and wire targets of 25-mu-m diameter have been studied. Using a PET Bragg crystal as the dispersive element, a resolving power of approximately 3500 was achieved with spatial resolution at the 5-mu-m level in frame times of the order of 80ps. Reduction of the data for times up to 150ps after the peak of the incident laser pulse produced estimates of the temperature and densities present, as a function of space and time.

Effect of laser intensity on fast-electron-beam divergence in solid-density plasmas

Metal foil targets were irradiated with 1 mu m wavelength (lambda) laser pulses of 5 ps duration and focused intensities (I) of up to 4x10(19) W cm(-2), giving values of both I lambda(2) and pulse duration comparable to those required for fast ignition inertial fusion. The divergence of the electrons accelerated into the target was determined from spatially resolved measurements of x-ray K-alpha emission and from transverse probing of the plasma formed on the back of the foils. Comparison of the divergence with other published data shows that it increases with I lambda(2) and is independent of pulse duration. Two-dimensional particle-in-cell simulations reproduce these results, indicating that it is a fundamental property of the laser-plasma interaction.

A nearly real-time high temperature laser-plasma diagnostic using photonuclear reactions in tantalum

A method of measuring the temperature of the fast electrons produced in ultraintense laser-plasma interactions is described by inducing photonuclear reactions, in particular (gamma,n) and (gamma,3n) reactions in tantalum. Analysis of the gamma rays emitted by the daughter nuclei of these reactions using a germanium counter enables a relatively straightforward near real-time temperature measurement to be made. This is especially important for high temperature plasmas where alternative diagnostic techniques are usually difficult and time consuming. This technique can be used while other experiments are being conducted. (C) 2002 American Institute of Physics.

Extreme ultraviolet line emission at 24.7 nm from Li-like nitrogen plasma produced by a short KrF excimer laser pulse

Recently using KrF high power laser (248 nm; 350 fs; 5.0x10(16) W/cm(2)) in the Rutherford Appleton Laboratory an experimental search for recombination extreme ultraviolet (XUV) laser action in Li-like nitrogen ions was performed. To understand the experimental results of line emission at 24.7 nm in the 3d(5/2)-2p(3/2) transition of the Li-like nitrogen ion a simulation was undertaken using a one-dimensional Lagrangian hydrodynamic code. From the simulation results, we confirmed that there was nonlinear dependence of spectral line emission on the gas density which was well matched to the experimental results. Only a six times increase of the 24.7 nm emission intensity was obtained when the plasma length was increased 1000 times from 1 mu m as an optically thin case to 1 mm. Also, the spatial profile of the electron density and temperature was obtained and the electron temperature was about 40-50 eV which was too high for the optical field ionization x-ray lasing. We could not find evidence of x-ray laser gain. (C) 1996 American Institute of Physics.

2ND-HARMONIC LIGHT GENERATION IN THE INTERACTION OF LASER-BEAMS WITH UNDERCRITICAL PLASMAS

The process of second harmonic generation (SHG) in undercritical plasmas is studied. It is shown that filamentation and self-focusing of the laser beam in the plasma can break the plasma density symmetry and lead to SHG by free electrons. In turn, second harmonic emission may be used to investigate the plasma parameters and to diagnose the process of laser beam filamentation itself.