Observation of MeV ions in long-pulse, large-scale laser-produced plasmas

A new approach for investigation of the generation of fast ions and hot electrons inside the same plasma volume in laser-produced plasmas is proposed. It is based on the spectroscopic observation of line radiation from singly and doubly excited levels with simultaneous high spectral and spatial resolution. The experimental results demonstrate the observation of fast ions from highly charged target material inside the plasma volume and suggest that the generally accepted scaling relations are seriously invalid under certain conditions. Even at rather modest intensities ions with energies of several MeV are observed. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 4, 262–267 (25 August 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Pulsations and chaos in laser-produced plasmas

A general criterion is proposed predicting the onset of chaotic behavior for parametric processes in a laser-produced plasma. The conditions when the transition to the stochastic regime occur are determined for various parametric instabilities excited when a high intensity laser interacts with a plasma. The complicated temporal structure observed in 3/2₀, 2₀, 1₀, and fast electron emission in experiments using high-intensity (I10^15–17 W/cm²), short ( _L 40–200 psec) Nd laser pulses is attributed to the reflection seeded SBS instability being driven into this regime.Lebedev Physics Institute, Leninsky Prospect 53, Moscow 117924 Russia.     

The importance of photoexcitation to the ionization dynamics of laser-produced carbon plasmas

The influence of temperature and density variations and opacity effects on the ionization dynamics of a spherical carbon plasma are determined. The calculations were done for solid, hollow and absorbing center geometries. The results of these calculations show that there are wide-spread differences in the amount and distribution of resonance line radiation emitted from the hydrogen- and helium-like ionization stages that depend on the model describing the ionization dynamics.     

Ionization effects in laser-produced plasmas

We describe a steady state density and temperature dependent atomic physics package TRIP (4) which we have incorporated into a 1-D lagrangian computer code MEDUSA. Using this modified version of the code we evaluate the degree of ionization and study the effect of atomic processes in laser-compression simulations of gas filled micro-balloons.     

Observation of megagauss-field topology changes due to magnetic reconnection in laser-produced plasmas

The spatial structure and temporal evolution of megagauss magnetic fields generated by interactions of up to 4 laser beams with matter were studied with an innovative, time-gated proton radiography method that produces images of unprecedented clarity because it uses an isotropic, truly monoenergetic back-lighter (14.7-MeV protons from D3He nuclear fusion reactions). Quantitative field maps reveal precisely and directly, for the first time, changes in the magnetic topology due to reconnection in a high-energy-density plasma (n(e) approximately 10(20)-10(22) cm(-3), T(e) approximately 1 keV).     

Density scalelength estimation in laser-produced plasmas

The relative intensities of the blue- and red-shifted satellites of three-halves harmonic spectra backscattered from plasmas produced by irradiation of targets with a high power Nd laser pulse have been measured. These have been used to estimate the plasma density scalelength due to the different emergent paths of each satellite.     

Filamentation and jets in line-focused laser-produced plasmas

In line-focused laser-produced plasma experiments on planar and cylindrical targets, we have observed the line-focused laser beam breakup into filaments as well as small-scale plasma jet-like structures. These phenomena might become obstacles in achieving optimum X-ray lasing in the type of experiments using line-focused laser-produced plasmas as a gain medium.     

Optical energy balance in laser-produced plasmas

Optical energy balance in plasmas produced by irradiating solid targets by highpower laser pulses, has been experimentally determined. The total light scattered has been measured as a function of the laser intensity and the irratiated spot diameter. It has been found that the net light absorption does not depend on the laser intensity alone, but is also affected by the irradiated spot area. It has also been observed that diffuse back reflection becomes a dominant loss mechanism at high incident flux and small irradiated spot area.     

Effect of self-generated magnetic field on the two-plasmon decay instability in a laser-produced plasma

Summary In this paper we have made a theoretical investigation on the two-plasmon decay instability of laser radiation in the presence of the selfgenerated magnetic field at the quarter-critical density region in a laserproduced plasma. The Vlasov equation in terms of guiding centre coordinates has been employed to obtain the nonlinear response of electrons in the plasma. The threshold power density of the incident laser radiation for the two-plasmon decay instability is always exceeded in currently employed power densities in laser-target experiments and above the threshold the growth rate of the instability is quite large. It is also noticed that the selfgenerated magnetic field enhances the threshold to a large extent, thus drastically reducing the growth rate of the instability. To speed up publication, the author of this paper has agreed to not receive the proofs for correction     

X-ray spectrometry of laser-produced aluminum plasmas

X-ray lines and continuum emission from a laser-produced aluminum plasma have been studied. The electron temperature variations during the laser pulse (30 ns) were deduced from time-dependent measurements of intensities of resonance lines (2.5 ns time-resolution). Comparison is made with electron temperature values deduced from ion emission measurements.     

High-order harmonic generation in nanoparticle-containing laser-produced plasmas

Nanoparticle-containing media can be used for the efficient high-order harmonic generation (HHG) of laser radiation in the extreme ultraviolet range. We review the results of recent studies of the HHG in laser-produced plasmas containing Ag, Au, Pd, Pt, Ru, GaN, BaTiO₃, and SrTiO₃ nanoparticles. The harmonics of femtosecond radiation up to the 55th order were achieved using the nanoparticle-containing plumes, when the femtosecond radiation propagated through the preformed plasma. These results are compared with the high-order harmonics generated from the plasma produced on the surface of bulk targets at different delays between the subnanosecond heating prepulse and femtosecond pulse. We discuss a six-fold enhancement of the HHG yield, which was achieved in the case of nanoparticle-containing plumes with regard to the monoparticle-containing plasmas.     

Observation of Stark-shifts of Lyman-α lines of low-Z ions in laser-produced plasmas

Red-shifts have been observed for Lyman-α lines of Z = 4–7 ions at an electron density of 10²¹ cm^-3. The plasma was produced by a 0.1 TW 100 ps glass laser. The shift was measured relative to the line center of the spatially resolved unperturbed line. The results are compared with theory.