References11

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Abstract The electron-ion and electron-electron collision frequencies in a highly ionized plasma are determined for drift velocities greatly exceeding the therm

We have measured the absorption of 1-ps laser pulses interacting with matter at intensities from 10/sup 10/ to 10/sup 16/ W/cm/sup 2/. The variations of absorption with incidence angle and polarization have been used to infer submicron plasma-density-gradient scale lengths. The results show a transition between a regime of laser interaction with sharply bounded dense cold matter (Iless than or equal to5 x 10/sup 12/ W/cm/sup 2/), where absorption is by the usual skin depth effect, to a regime of...

We describe temporal and spectroscopic measurements of high-density plasmas produced by focusing intense, 160-fsec laser pulses on solids. Soft x-ray emission with a duration of 2 +- 2 psec is observed up to photon energies of a kilovolt. We observe reduced emission from long-lived spectral lines, indicating the presence of a short-lived, high-density plasma. Reflectivity measurements indicate that absorption of the laser pulse occurs at the surface of the solid before it expands.

When an intense electromagnetic wave is incident obliquely on a sharply bounded overdense plasma, strong energy absorption can be accounted for by the electrons that are dragged into the vacuum and sent back into the plasma with velocities vapprox. =v/sub osc/. This mechanism is more efficient than usual resonant absorption for v/sub osc//..omega..>L, with L being the density gradient length. In the very high-intensity CO/sub 2/-laser--target interaction, this mechanism may account for most of t...

Experimental information on laser-induced multiple ionization is analyzed in terms of a model that includes the scaling of the generalized cross sections and the time dependence during the pulse. A comparison of direct with sequential processes reveals the dominance of the latter. The role of multiply excited states in strong-laser studies is also discussed.

The force exerted by a high-frequency electric field on a macroscopic body is calculated. Starting from total momentum conservation, a rigorous definition of radiation force density is given, and the relationship between a time-averaged Maxwellian stress tensor and radiation pressure is clarified. Formulas are presented for calculating the volume force density of the radiation-force term. It is further shown that all resonant wave–wave interactions of nonlinear optics, such as stimulated Brillou...

Inverse bremsstrahlung absorption in strong radiation fields during binary collisions: 'straight-line path' approximation

Considers the relationship between the impact, Born and 'straight-line path' approximations and the overlap of the regions of applicability. Particular emphasis is given to a perturbative fully classical model of the electron motion. It is shown that the perturbative fully quantum-mechanical approach (Born approximation) leads to a formally similar result. The impact approximation is shown to exist as an asymptotic limit. These results are used to study the role of cut-offs for Coulomb scatterin...

Inverse bremsstrahlung absorption in large radiation fields during binary collisions-classical theory

The approach allows calculations to be made of the absorption at any field strength provided the field is classical and the electron is nonrelativistic and its thermal distribution function is isotropic. Calculations are made for electron/atom collisions interacting by a power law central force. The results are extended to discuss absorption in plasmas. The effects of electron-electron and inelastic collisions are also considered.

Electron-impact ionization cross-sections and ionization rate coefficients for atoms and ions from scandium to zinc

Using the empirical formula recently proposed, electron-impact ionization cross-sections for single ionization from the ground state are given for free atoms and for nearly all ionization stages from scandium (Z=21) to zinc (Z=30). For these species ionization rate coefficients are given under the assumption of a Maxwellian distribution of the impacting electrons. Multiple ionization, lowering of ionization potential, or collision limit are not taken into account.

Electron Impact Ionization Cross-Sections and Ionization Rate Coefficients for Atoms and Ions from Hydrogen to Calcium

Using the empirical formula recently proposed, electron-impact ionization cross-sections for single ionization from the ground state are given for free atoms and for all ionization stages from hydrogen to calcium (Z=20). Ionization rate coefficients are given for these species on the assumption of a Maxwellian distribution of the impacting electrons. Multiple ionization, lowering of ionization potential, or collision limit are not taken into account.

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Inverse bremsstrahlung absorption of electromagnetic radiation in plasma with anisotropic two-temperature bi-Maxwellian electron distribution function over velocities is investigated. In the case of a weak field, absorption is more effective if the radiation field is polarized in the plane in which the plasma electrons have the smaller of the two temperatures. In the case when the distribution function is highly anisotropic, absorption changes strongly when the field polarization changes its dir...

The interaction of high power lasers with plasmas has been an active field of research for over 30 years. Motivated primarily by inertial confinement fusion1 and x-ray laser research,2 most studies have used nanosecond pulse gas lasers — CO2 lasers in the early days, then excimer (KrF and XeCl) lasers — and solid state Nd:glass lasers, eventually frequency up-converted to 0.53µm (2ω0), O.34µm (3ω0), and O.26µm (4ω0). Laser-plasma interaction physics has been studied extensively to explore the ef...

A class of nonlinear optical effects related to fast field ionization in an interference pattern is investigated by numerical simulations. Interference between counter-propagating ultra-short pulses slightly below the ionization threshold produces a layered distribution of free-electron density. In a dense dielectric target, this effect allows us to trap light between plasma layers creating a sort of optical microcavity. Other peculiar features include frequency upshift, pulse lengthening and se...

Second and third harmonic generation in the interaction of a prepulse-free 700-fs, 248-nm laser pulse with solid targets was observed for maximum intensities of /spl sim/5.10/sup 15/ W/cm/sup 2/. Both s- and p-polarized light generated harmonic emission without observable difference. Harmonic generation was shown to prefer the specular direction. The results showed short-pulse ultraviolet lasers to be efficient drivers of harmonics in the vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) ra...

Picosecond laser pulses at a wavelength of 266 nm have been focused onto a solid metal cathode in coincidence with high gradient electric fields to produce high brightness electron beams. At power densities exceeding 109 W/cm2, a solid density plasma is formed and intense bursts of electrons are emitted from the target accompanied by macroscopic surface damage. An inferred ∼1 μC of integrated charge with an average current of ∼20 A is emitted from a radio‐frequency cavity driven at electric fiel...