Laser-generated electron emission from surfaces: Effect of the pulse shape on temperature and transient phenomena

Lin, Jui‐Teng; George, Thomas F.

doi:10.1063/1.331713

Cited by 51 publications

(11 citation statements)

References 15 publications

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“…In fact, charge carriers may reach thermal equilibrium in about 10 s, but, due to electron-phonon interactions which seem to have a positive feedback, there is also a very fast energy transfer to the lattice which is complete in about 10 s [1]. The form of the laser-pulse intensity Ip adopted in our simulation will be taken as "triangular" [6]: ductivity (units as in Table I) and S(x, t) is the heat source term given by Eq. (1) multiplied by p. The quantities c, p, and K will be subsequently assumed to be temperature and space independent.…”

Section: Absorption Of the Laser Radiationmentioning

confidence: 99%

Laser-pulse sputtering of aluminum: Vaporization, boiling, superheating, and gas-dynamic effects

Peterlongo¹,

Miotello²,

Kelly³

1994

Phys. Rev. E

157

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We have developed a numerical method to describe laser-pulse sputtering of Al in a thermal regime. The irradiation consists of a single pulse of triangular form having a duration of 30 ns. The laser light is assumed to be absorbed according to a simple exponential mechanism. Heat transport in the Al is described by the heat Bow equation with boundary conditions for vaporization, with or without boiling. Vaporization rates are evaluated by the Clausius-Clapeyron law and the boiling mechanism (when boiling is assumed to be possible) is implemented as soon as the vapor pressure reaches 1 atm. A critical analysis of the time scales necessary for true boiling, as well as for superheating above the boiling temperature, is made in order to understand the relevance of these phenomena with respect to particle emission from the Al surface. Moreover, on the basis of the calculated vaporization rates, it is possible to distinguish between different gas-dynamic regimes. When the rate is less than 1 ML in 20 ns, the particles emerging from the surface do not achieve local thermal equilibrium, and therefore undergo free Bight describable by a modified Maxwellian. When the rate is 1 ML in 20 ns, a Knudsen layer forms, at the boundary of which particles achieve local thermal equilibrium and only subsequently undergo free Bight. Finally, when the rate is sufBciently greater than~1 ML in 20 ns, the gas dynamics of the particles leaving the Knudsen layer may be described with the gas-dynamic equations, if the density is high enough, or, otherwise, by the Boltzmann equation. Numerical results concerning the effectiveness of laser sputtering in producing craters in irradiated Al, as well as the main features of the gas dynamics (including recondensation or re6ection of the gas at the Al surface), are illustrated.

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Section: Absorption Of the Laser Radiationmentioning

confidence: 99%

Laser-pulse sputtering of aluminum: Vaporization, boiling, superheating, and gas-dynamic effects

Peterlongo¹,

Miotello²,

Kelly³

1994

Phys. Rev. E

157

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“…In this regime, the efficiency increases as the accelerating voltage increases as again justified by the Schottky effect and equation. (10).…”

Section: Resultsmentioning

confidence: 95%

“…It is important even to stress that the plasma is responsible for the short circuits present in the diode gap at high accelerating voltage. From equation (10), the current increase can be due only to a decreasing of the effective work function. It diminishes as the electric field increases.…”

Section: Resultsmentioning

confidence: 97%

Photo-emission studies from Zn cathodes under plasma phase

Belloni¹,

Caretto²,

Lorusso³

et al. 2005

Radiation Effects and Defects in Solids

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In this paper, we report investigations of the electron emission from pure Zn cathodes irradiated by UV laser pulses of 23 ns (full-width at half-maximum) at a wavelength of 248 nm (5 eV). The metal cathodes were tested in a vacuum photodiode chamber at 10 −5 Pa. They were irradiated at normal incidence and the anode-cathode distance was set at 3 mm. The maximum applied accelerating voltage was 18 kV, limited by the electrical breakdown of the photodiode gap. Under the above experimental conditions, a maximum applied electric field of 6 MV/m resulted. In the saturation regime, the measured quantum efficiency value increased with the accelerating voltage due to the plasma formation. The highest output current was achieved with 14 mJ laser energy, 18 kV accelerating voltage and its value was 12 A, corresponding to a global quantum efficiency (GQE) approximately of 1 × 10 −4 . The temporal quantum efficiency was 1.0 × 10 −4 at the laser pulse onset time and 1.4 × 10 −4 at the pulse tail. We calculated the target temperature at the maximum laser energy. Its value allowed us to obtain output pulses of the same laser temporal profile. Tests performed with a lower laser photon energy (4.02 eV) demonstrated a GQE of two orders of magnitude lower.

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“…The laser pulse shape was assumed to be a triangular, with rising and falling times equal to the pulse width. This assumption well approximates the Gaussian time dependence [17]. The dotted and solid lines represent the calculation results obtained using the calculated reflectivity and experimental reflectivity, respectively.…”

Section: Current Lidt Data and Numerical Assessmentmentioning

confidence: 95%

Assessment of Laser Transmission Mirror Materials for ITER Edge Thomson Scattering Diagnostics

Kajita

Hatae

Voitsenya

2008

Plasma and Fusion Research

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An assessment of in-vessel metallic mirror materials for the transmission of the laser beam used in the ITER edge Thomson scattering diagnostics is reported. The transient temperature increase due to the laser pulse irradiation on the laser transmission mirror is calculated by a one-dimensional heat conduction equation. Candidate mirror materials are discussed based on a comparison between the numerical calculation and current data relevant to the laser-induced damage threshold (LIDT). Gold, silver, and copper are considered promising because of its high reflectivity. The LIDT is evaluated considering multi-pulse effects and used to determine the necessary size for the laser transmission mirror for the ITER edge Thomson scattering diagnostics.

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Laser-generated electron emission from surfaces: Effect of the pulse shape on temperature and transient phenomena

Abstract: Reproduction in whole or in part is permitted for any purpose of the United States Government. This document has been approved for public release and sale; its distribution is unlimited.

Cited by 51 publications

References 15 publications

Laser-pulse sputtering of aluminum: Vaporization, boiling, superheating, and gas-dynamic effects

Laser-pulse sputtering of aluminum: Vaporization, boiling, superheating, and gas-dynamic effects

Photo-emission studies from Zn cathodes under plasma phase

Assessment of Laser Transmission Mirror Materials for ITER Edge Thomson Scattering Diagnostics

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