The interaction of powerful laser and X-ray pulses
with planar low average density (0.5–10 mg/cm3)
porous agar-agar targets was experimentally studied. At
a laser power density of ∼5 × 1013
W/cm2 (λ = 1.054 μm) the laser light
absorption and following energy transfer processes, as well
as dynamics of produced plasma were investigated in detail
with a variety of optical and X-ray diagnostic methods. Volume
absorption is shown to occur in experiments with laser-irradiated
agar targets. An extended laser energy deposition region filled
with hot (0.8–1 keV) plasma is formed inside a porous
target. The laser light absorption efficiency is as high as ∼80%.
The emission of 2ω0 and 3ω0/2 harmonics
from laser-produced plasma is observed over the time of the laser pulse
even with agar targets of 0.5 mg/cm3 average density.
Characteristics of energy transfer in low-density porous media are
measured in experiments on illumination of agar targets by laser
pulses or X rays emitted by a thin Cu converter. The hydrodynamic
mechanism is responsible for the energy transfer in laser-illuminated
porous targets and the radiative energy transfer seems to be dominant
in the case of X-ray irradiation. The experimental data are in
reasonable agreement with predictions of a developed theoretical model
describing the hot plasma layer formation and the two-stage homogenization
process within the illuminated porous targets.