Semiclassical Theory of Ion Stopping

More, R.M.; Warren, K.H.

doi:10.1051/jphyscol:1988707

Cited by 6 publications

(11 citation statements)

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“…Results are consistent with conductive heating of the first 1000 Å. [S0031-9007(96)00721-1] PACS numbers: 52.70.Nc, 52.40.Nk, 52.50.Jm, 52.65.Kj Recent advances in high intensity sub-ps laser technology have allowed new regimes of hot dense matter to be investigated [1][2][3][4][5][6]. Plasmas in the kilovolt temperature range at near solid densities are relevant to areas such as intense x-ray source development [6] and for inertial confinement fusion applications [7].…”

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“…Hydrodynamic simulations relate the measured velocities to the sound speed, determining the temperature along the central axis of the plasma. Results Recent advances in high intensity sub-ps laser technology have allowed new regimes of hot dense matter to be investigated [1][2][3][4][5][6]. Plasmas in the kilovolt temperature range at near solid densities are relevant to areas such as intense x-ray source development [6] and for inertial confinement fusion applications [7].…”

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Electron Temperature Measurements of Solid Density Plasmas Produced by Intense Ultrashort Laser Pulses

1996

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We report the first spatially and temporally localized measurements of 500 eV electron temperatures in solid density Al plasmas generated by a 3 3 10 17 W͞cm 2 , 170 fs laser. Expansion velocities of marker layers from various depths are sampled with mass-resolved ion time-of-flight spectroscopy. Hydrodynamic simulations relate the measured velocities to the sound speed, determining the temperature along the central axis of the plasma. Results are consistent with conductive heating of the first 1000 Å. [S0031-9007(96)00721-1] PACS numbers: 52.70.Nc, 52.40.Nk, 52.50.Jm, 52.65.Kj Recent advances in high intensity sub-ps laser technology have allowed new regimes of hot dense matter to be investigated [1][2][3][4][5][6]. Plasmas in the kilovolt temperature range at near solid densities are relevant to areas such as intense x-ray source development [6] and for inertial confinement fusion applications [7]. The macroscopic properties of these plasmas are determined by complex interactions such as laser absorption mechanisms at high intensities [4,5], and the generation and transport of radiation [8-10] and particle fluxes [11][12][13][14].Dense, high temperature plasmas are typically studied by x-ray spectroscopy, particle emission, and Doppler shift spectroscopy. Ion time-of-flight (TOF) measurements have been used previously to determine suprathermal electron temperatures of plasmas produced by lasers with pulse lengths from 1 ps [15] to 1 ns [16]. Ion energy distributions with MeV proton energies have recently been reported from 3 ps laser pulses [17]. Spatially and temporally averaged x-ray spectra of sub-ps laser produced plasmas have shown electron temperatures of a few hundred eV [9,10]. However, determining the peak temperature from x-ray spectra is problematic, since the fastest reported x-ray streak camera response is 0.89 ps [18], while simulations presented here indicate cooling times of a few hundred femtoseconds. Attenuation of cold Ka emission with depth in the target has been used to measure the suprathermal electron temperature [13,14] but does not measure the thermal electron temperature. Doppler shift measurements have been used to determine temperatures at lower intensities [19,20] but interpretation requires the inclusion of ponderomotive effects above 10 17 W͞cm 2 [21].For sub-ps laser heating, solid density plasmas are produced with scale lengths shorter than the laser wavelength.Hydrodynamic expansion of such plasmas should be relatively simple to measure and interpret theoretically. Ions from the surface expand during the laser pulse, and therefore are driven by an electron distribution which may contain a suprathermal component. For the plasma conditions of this Letter, expansion from depths greater than ϳ100 Å occurs after the laser pulse, and therefore is driven only by thermal electron pressure. Thus, expansion velocities from surface and embedded materials are indicative of suprathermal and thermal temperatures, respectively. The work presented in this Letter is novel in that embedded la...

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Electron Temperature Measurements of Solid Density Plasmas Produced by Intense Ultrashort Laser Pulses

1996

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“…+ p Amplified, high contrast femtosecond laser pulses [1] have opened a new regime of laser-solid interactions in which intense light is deposited into a solid faster than the target surface can hydrodynamically expand [2]. While numerous experiments have used a single pulse to both excite and probe such sharply bound solid density fluids [3], they have not individually identified the many competing collisional and collisionless absorption mechanisms unique to this regime which an extensive theoretical literature [4][5][6][7][8][9][10] has enumerated.…”

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Experimental Identification of “Vacuum Heating” at Femtosecond-Laser-Irradiated Metal Surfaces

et al. 1999

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Aluminum and iron targets were irradiated by intense (I # 10 15 W͞cm 2 ), 120 fs laser pulses with sufficiently high contrast such that the surface expanded no more than the peak electron quiver amplitude during excitation. Under these experimentally verified conditions, obliquely incident, p-polarized pulses uniquely experienced anomalous absorption, proportional to ͑Il 2 ͒ 0.64 , and as high as 20%. This extra absorption was distinguished from competing pump-induced linear mechanisms by fs-time-resolved reflectivity, and agreed quantitatively with essential features of Brunel's "vacuum heating," in which light is absorbed by drawing electrons into the vacuum and sending them back into the plasma with approximately the quiver velocity. [S0031-9007 (99)09116-4] PACS numbers: 52.50.Jm, 78.20.Ci, 78.47. + p Amplified, high contrast femtosecond laser pulses [1] have opened a new regime of laser-solid interactions in which intense light is deposited into a solid faster than the target surface can hydrodynamically expand [2]. While numerous experiments have used a single pulse to both excite and probe such sharply bound solid density fluids [3], they have not individually identified the many competing collisional and collisionless absorption mechanisms unique to this regime which an extensive theoretical literature [4-10] has enumerated. For example, Brunel [4] proposed over ten years ago that a moderately intense, p-polarized light pulse incident obliquely on an atomically abrupt metal surface could be strongly absorbed by pulling electrons into the vacuum during an optical cycle, then returning them to the surface with approximately the quiver velocity. Later simulations [5] predicted that, with a slight surface expansion of scale length L ϵ ͑≠ lnn e ͞≠z͒ 21 , the optical field would pull more electrons into the vacuum, and thus be even more strongly absorbed, as long as L did not significantly exceed the electron quiver amplitude x osc eE͞mv 2 . While this "vacuum heating" (VH) mechanism has been incorporated into laser-plasma codes [6], and may influence surface x-ray [11] and high harmonic [12] generation, and intense laser interaction with nanoclusters [13] and hollow capillaries [14]-and although a microscopically similar mechanism underlies high harmonic generation and above-threshold ionization in gases [15]-quantitative experimental identification of VH at metal surfaces is completely lacking.Two important barriers to such identification have been the production and verification of Brunel's condition L & x osc , and distinction of VH from competing linear mechanisms [7] such as inverse bremsstrahlung (IB), anomalous skin effect (ASE) [8], sheath inverse bremsstrahlung (SIB) [9], sheath transit absorption (STA) [10], and resonance absorption (RA) [16]. For example, 120 fs pulsed excitation at l 0.62 mm and peak intensity I 10 15 W͞cm 2 heats Al targets to a peak electron temperature of kT e ϳ 100 eV [3,7], resulting in a collision frequency n ϳ 5 3 10 15 s 21 [7]. For L 0, IB dominates under these conditions...

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“…This approximation, usually called the Kramers formula (Zeldovich & Raizer 1966), is Equation (1) does not seem very accurate even for hydrogen, yielding 40% higher values than quantum results; furthermore, it is evaluated for isolated ions only. For nonhydrogenic atoms within the context of the screened hydrogenic model, More (1986) proposed the / expression J ""' Using the semiclassical WKB approximation, More and Warren (1988) developed the oscillator strength formula f nr_ 2m (F max(/,Q . .,.…”

Section: Review Of the Oscillator Strength Formulationmentioning

confidence: 99%

Analytical approximation for oscillator strengths of H-like ions

Mı́nguez

1990

Laser Part. Beams

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The main objective of this work is to find analytical formulas for the oscillator strength / of hydrogen-like ions. It is well known that / is proportional to the energy of the transitions between eigenstates (A£), and to the square of the R matrix. Therefore, the problem of calculating / can be reduced to finding analytical expressions for both parameters, AE and R. Hence these expressions would be in accordance with quantum results based on more sophisticated calculations.

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Semiclassical Theory of Ion Stopping

Cited by 6 publications

References 0 publications

Electron Temperature Measurements of Solid Density Plasmas Produced by Intense Ultrashort Laser Pulses

Electron Temperature Measurements of Solid Density Plasmas Produced by Intense Ultrashort Laser Pulses

Experimental Identification of “Vacuum Heating” at Femtosecond-Laser-Irradiated Metal Surfaces

Analytical approximation for oscillator strengths of H-like ions

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