Kinetic Energies of Ions Produced by Laser Giant Pulses

Gregg, D.W.; Thomas, Scott J.

doi:10.1063/1.1708034

Cited by 51 publications

(8 citation statements)

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“…The keV ions should only form part of the plasma produced, as observed [26,33], but may cause anomalous absorption due to the nonlinear force, as was observed in gas breakdown [32]. The nonlinear onset [25,26] of the process at powers P exceeding 1 MW is evident, but its sublinear continuation [27] may be explained by the fact that the bent surface at the beginning of the filaments will cause some saturation. This bending may also cause some large divergence of the nonlinearly created ion beam, while under plane conditions (without self-focusing) at I~ 1014 W/cm 2 very well-directed ion emission with small beam divergence should characterise the nonlinearly accelerated ions, as Lindl and Kaw [11] pointed out.…”

Section: Discussionmentioning

confidence: 86%

“…It may still be considered an anomaly that Linlor [25] observed at laser powers of l0 s W maximum ion energies gimax of the thermal kind of a few eV, while keV ions occurred at l0 T W. The strong superlinear increase of eim~x with the laser power P was measured very carefully by Namba, Schwarz et al and before [26], while eimax increased sublinearly [27] with P at P~ 100 MW. The special effects at P around 106 W were also seen from the electron emission of laser produced plasmas.…”

Section: Discussionmentioning

confidence: 96%

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Self-focusing and nonlinear acceleration process in laser produced plasma

Hora

1970

Opto-electronics

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Ruby laser intensities exceeding/* -101' W/cm 2 create a predominant acceleration of dense plasma due to nonlinear collisionless interaction resulting mainly from collective effects. Recoil causes confinement of the plasma interior in the form of a superlinearly increased radiation pressure. Similar nonlinear forces produce selffocusing in plasmas at a threshold laser power of only 10' to 10' W. The resulting filaments have intensities/*, from which their diameter can be determined in agreement with measurements of Korobkin and Alcock. These high intensities should allow some observed properties of laser produced plasmas (keV ions, linear increase of the ion charge) to be interpreted on the basis of the nonlinear acceleration described. IntroductionWhen intense laser radiation interacts with dense materials, e.g. gases or solids, many complicated processes occur. After absorption of the radiation, heating, evaporation, and ionisation of the material, the plasma is subjected to an expansion process. The energy of the light is transferred at least initially by a thermalisation process into the plasma, where electron collisions cause an inverse bremsstrahlung mechanism. Besides this process there is direct interaction between the laser light and the plasma owing to collective effects of the electrons. This leads to acceleration of the plasma due to a nonlinear force. The mechanism can be described as a collisionless nonlinear absorption process.Section 2 presents the essential properties of the acceleration process and shows that the nonlinear force is a special part of Landau and Lifshitz's formulation [1] of the ponderomotive force if the collective effects are essential. The mechanism can still be described non-relativistically, and the relativisitic change of the plasma frequency I-2] is still negligible. The properties of the force are described according to a modification of a preceding derivation I-3].Section 3 describes some analytic integrations of the nonlinear force, resulting in the momentum being transferred to the plasma surface region, which is accelerated by a pressure exceeding the radiation pressure by a factor up to more than one hundred. The resulting ion energy increases superlinearly relative to the laser intensity if the electrons have a higher energy due to coherent oscillation than to random (thermal) motion, this being the case at intensities around I* ~ 1014 W/cm 2 for ruby or neodymium lasers.Section 4 confirms the predominance of the nonlinear force over the gasdynamical (thermokinetic) forces at laser intensities 1 > I*. This threshold is also the intensity at which a nonlinear decrease of the collision frequency starts, causing a decrease of the collision induced absorption constant at higher or increasing intensity L This behaviour was deduced on the

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Section: Discussionmentioning

confidence: 86%

Section: Discussionmentioning

confidence: 96%

Self-focusing and nonlinear acceleration process in laser produced plasma

Hora

1970

Opto-electronics

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“…arbitrary units Figure 1.1 Nearly linear increase of the ion velocity with the laser power P at laser irradiation with about 10 MW (after Isenor [65]). and higher laser power (after Gregg and Thomas [68]). …”

Section: Review Of Phenomena and Resultsmentioning

confidence: 99%

Plasmas at High Temperature and Density

Hora¹

1991

Lecture Notes in Physics Monographs

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Preface"New physics" is an appealing new keyword, not yet devalued by the ravages of inflation. But what has this to do with such an ugly field as plasma physics, steeped in classical physics, mostly outworn, with all its unsolved and ambiguous technological problems and its messy and open ended numerical studies?"New physics" is concerned with quarks, Higgs particles, grand unified theory, superstrings, gravitational waves, and the profound basics of cosmology and black holes. It is the field of astonishing quantum effects, demonstrated by the von Klitzing effect and hightemperature superconductors. But what can plasma physicists offer, after so many years of expensive and frustrating research to solve the problem of fusion energy?One may suggest that the fascinating research of chaos with applications to plasma, or the achievements of statistical mechanics applied to plasmas, has something to offer and should be the subject of attention. However, this is not the aim of this book.Complementing the traditional aim of physics, which is to interpret the phenomena of nature by generalizing laws such that exact predictions about new properties and effects can be drawn, this book demonstrates how new physics has been derived over the last 30 years from the state of matter which exists at high temperatures (plasma). The advent of the laser, with its very high energy densities and its concentration to extremely small volumes and to very short time periods, opened up a whole new regime for the interaction of materials and high-density plasmas, which enforced the appearance of the "rather new physics".Here are a few examples:• Who would have expected that optical waves in vacuum have a longitudinal component? Thomas Young discovered in 1801 the pure transversality of optical radiation. This was not understandable at that time, when it was known that mechanical waves never exist without longitudinal components. Maxwell's equation then only revealed solutions of the purely transverse plane waves in electromagnetism. Against all this traditional knowledge, the recent findings about the dynamics of electrons driven by laser beams by nonlinear forces led to thẽ xact derivation of longitudinal optical wave components.• The same nonlinear force interaction, in view of momentum transfer in experiments, led to the clarification of the angular momentum ofoptical beams and brought about the first substantiation of the photon spin by a macroscopic property.• The conditions of very high laser intensities led to nonlinear and relativistic generalization of the optical response (dielectrics and absorption) with a prediction of relativistic self-focusing to understand how GeV ions are produced by laser irradiation of solid targets.• The quantum generalization of Coulomb collisions in plasmas at high temperatures explains the anomalous resistivity, in agreement with observations where links are given between the simply derived Coulomb collision frequency and quantum electrodynamics, including stimulated emission. IX that after the first l...

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“…This investigation deals with the kinetic energy of evaporated ions, determined by time of flight measurements [26][27][28][29]. Time of flight (TOF) studies of the plasma give vital information regarding the time taken by a particular state of the constituents to evolve after the plasma is formed.…”

Section: Tof Studies In Ag Plasma Using the Faraday Cup Ion Probe Methodsmentioning

confidence: 99%