The model of plasma production by laser radiation onto a solid target
was developed taking into account plasma heating by the emitted electrons
and target heating by ion bombardment, as well as by the laser radiation.
The near target plasma structure was analyzed. The space charge sheath was
studied solving the Poisson equation and taking into account the volume
charge of accelerated electrons and ions. The kinetics of atoms evaporated
from the target and the back-flow of atoms and ions from the plasma
towards the surface was analyzed. A system of equations, including
equations for solid heat conduction, plasma generation and the plasma
expansion was formulated. The calculation for Cu target, laser spot radius
100 μm, pulse duration 1 ms, 103, 10, 1ns and laser power
density qL = 10−3–1
GW/cm2 was conducted. The ratio of net evaporation rate to
the total evaporated mass flux was determined. It was shown that the
plasma mainly generated in the electron emission beam relaxation region
and there the plasma flow is subsonic. The electric field at the target
surface is relatively large and therefore the ion current to the surface
in the space region is large and comparable with the electron emission
current. A large contribution of the plasma energy flux in the target heat
regime was obtained, showing that the laser generated plasma significantly
converts the absorbed laser energy to kinetic and potential energy of the
plasma particles, which transport part of the energy through the
electrostatic sheath to the solid surface.
Laser plasma generation and plasma interaction with ablative
target