Chapter 2
Laser Absorption by Coulomb Collision
2.1 Plasma Generation by Lasers
2.1.1 Field-Induced Electron Emission
Plasma production in laboratory has started with gas discharge in a low-pressure gas
in a glass tube by applying high voltage between the minus and pulse electrodes. The
material of the minus side, cathode, is metal in general. The electric potential
structure of binding energy to an electron is schematically shown in Fig. 2.1.
Metal confines many free electrons, and their maximum energy at zero temperature
is called Fermi energy, Ε F , which is only a function of electron density. The electric
potential near the metal surface is in general of a profile given by black in Fig. 2.1.
The potential difference from the inside of metal to the vacuum is called work
function W. For example, usual metals have the work function of, for example,
4.4 eV [Cu], 4.25 eV [Al], 4.5 eV [W], and so on.
When a high voltage is imposed to the surface of such metals, the electric field by
the high voltage alters the electric potential structure as shown by green in Fig. 2.1.
In the case where the external electric field is high enough, it is possible for the
electrons in the metal to come out through the metal surface. This is due to the
tunneling effect well-known in quantum mechanics. Such ionization is called fieldinduced emission.
The emission rate of the electrons from the metal surface is approximately
calculated by the use of WKB method. Given the external electric field E in z
direction perpendicular to the metal surface, the effective potential to the electron is
in the form:
© Springer Nature Switzerland AG 2020
H. Takabe, The Physics of Laser Plasmas and Applications - Volume 1, Springer
Series in Plasma Science and Technology,
https://doi.org/10.1007/978-3-030-49613-5_2
29
Laser Absorption by Coulomb Collision
2.1 Plasma Generation by Lasers
2.1.1 Field-Induced Electron Emission
Plasma production in laboratory has started with gas discharge in a low-pressure gas
in a glass tube by applying high voltage between the minus and pulse electrodes. The
material of the minus side, cathode, is metal in general. The electric potential
structure of binding energy to an electron is schematically shown in Fig. 2.1.
Metal confines many free electrons, and their maximum energy at zero temperature
is called Fermi energy, Ε F , which is only a function of electron density. The electric
potential near the metal surface is in general of a profile given by black in Fig. 2.1.
The potential difference from the inside of metal to the vacuum is called work
function W. For example, usual metals have the work function of, for example,
4.4 eV [Cu], 4.25 eV [Al], 4.5 eV [W], and so on.
When a high voltage is imposed to the surface of such metals, the electric field by
the high voltage alters the electric potential structure as shown by green in Fig. 2.1.
In the case where the external electric field is high enough, it is possible for the
electrons in the metal to come out through the metal surface. This is due to the
tunneling effect well-known in quantum mechanics. Such ionization is called fieldinduced emission.
The emission rate of the electrons from the metal surface is approximately
calculated by the use of WKB method. Given the external electric field E in z
direction perpendicular to the metal surface, the effective potential to the electron is
in the form:
© Springer Nature Switzerland AG 2020
H. Takabe, The Physics of Laser Plasmas and Applications - Volume 1, Springer
Series in Plasma Science and Technology,
https://doi.org/10.1007/978-3-030-49613-5_2
29