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The applicability of hydrodynamic models for theoretical
description of UV laser ablation of polymers is studied.
The plume formation is considered as a first-kind phase
transition. In case of strongly absorbing polymers this
phase transition occurs as a surface evaporation, and in
case of weakly absorbing polymers as a bulk evaporation.
The vapor plume is assumed to be transparent for laser
radiation, and its expansion is described by the isoentropic
hydrodynamic equations. New analytical expressions for
ablation (etch) depths per pulse are obtained, which are
in good agreement with the available experimental data
(Afanasiev et al. 1997).
The experiments to study the indirect drive targets'
dynamics in a highly symmetrical X-radiation field were
performed on the ISKRA-5 facility. This paper covered the
results of experiments with the targets in the form of
a Cu spherical hohlraum, the internal surface of which
is coated with Au, with six holes for laser radiation input.
In the center of the aforementioned hohlraum, a glass capsule
filled with D–T gas was placed. In several experiments,
the central capsule was coated with an ablator made of
plastic with a different thickness. This allowed us to
perform a series of experiments in which the different
compression degree of D–T fuel was achieved. The
analyses of experimental results revealed good agreement
between the latter and the spherically symmetrical hydrodynamic
Two shells with the diameter of 0.8–0.9 mm
and a wall thickness of ≅1 μm were produced at
the Lebedev Physics Institute for the experiments conducted
at the ISKRA-5 facility. The results of two experiments
with the aforementioned shells conducted at the ISKRA-5
facility with the use of an indirect-drive set up. In one
of the experiments, the diameter of the golden hohlraum
was D = 2 mm while in the other it was D =
4 mm. In these experiments it was observed to be ≅4
times the difference of the average laser intensity on the
hohlraum surface. The results of computational analysis of the
experiments are also presented here.
The investigations of the influence of various
types of wavefront distortions, varying in time, on the
intensity distribution on the surface of a target are carried
out. It is shown that distortions of a wavefront, equivalent
to transverse displacement in time of a beam in far field
at an angle of approximately 10 diffraction angles, results
in practically full smoothing of a specl-structure of intensity
distribution. Creation of phase distortions of a beam assigned
as running in a cross section wave with an amplitude of
more than 3 radian and with a spatial size exceeding 20–30
times the size of the kinoform phase plate element, permits
us to reduce the depth of modulation in distribution of
intensity in far field also. The capability of application
is considered as a smoothing device of the dynamic plasma
layer, based on the volume-structured medium. The model
of energy transport process in such media is developed.
Matching of calculation and experimental results is conducted.
Electromagnetic emission at the plasma frequency
ωp and its harmonics
nωp has been
studied. Although such emission is well known from very
low density plasmas (electron density of the order of
ne ≈ 108
cm−3) now, for the first time it has
also been observed from a high density plasma (electron
density of the order of ne ≈
1023 cm−3) produced by a
high-intensity femtosecond laser pulse. This radiation is
strongly connected to jets of high energy electrons produced
in such steep gradient plasmas by collective mechanisms, and
probably to nonlinear Langmuir waves in the overdense plasma
region. Theoretical investigations using particle-in-cell
simulations have been made to pinpoint the physical origin
and properties of the emission. Preliminary results show a
very weak scaling of the ωp and
2ωp emission with intensity, which
should provide clues for future theoretical analyses. Although
not the main subject of the present work, also harmonics up
to the 20th of the laser fundamental may have been
observed close to the ωp and
2ωp line emission in the present
experiment (PACS numbers: 52.40.Nk, 42.65.ky, 52.65.-y,
Results of turbulent mixing research of thin Al
and Au layers under laser acceleration of the three-laser
targets Si/Al/Au are presented. Analyses of experimental
data under the program SND-TUR, where the Nikiforov model
is used for turbulent mixing description, testify to the
essential impact of hot spots on the examined processes
in distribution of laser radiation intensity on the surface
of the target. Experimental setup on the laser beams'
smoothing by the “foam” coated on the target,
has been considered. The results of the first experiments
In the present study we performed an experimental
investigation of the Rayleigh–Taylor instability
(RTI) in a mixing zone between two gases entrapped into
accelerated motion by a nonstationary compression wave.
Acceleration g was ∼1.5·107
cm/s2, Atwood numbers ranged from 0.04 to 0.77.
A mixing zone was formed by an oxygen-hydrogen mixture
and an inert gas (Ne, Ar, Kr, Xe) or SF6. The
initial gas pressure was 0.5 atm. A specific feature of
our experiment is compressibility of media tested and initially
continuous interface between gases of different densities.
The present work is a continuation of investigations on
nonlinear, transition, and early turbulent stages of the
In this work, the Saha equation is solved using
atomic data provided by means of analytical potentials
to calculate the ionization state and ion abundances for
local thermodynamic equilibrium (LTE) plasmas of Al, Fe,
and Au. The plasma effects are taking into account using
an analytical potential which includes plasma effects.
The problem of the cut off partition functions in the Saha
equation is also analyzed using three different criteria.
Finally, some opacity calculations are performed.
Presently, a great part of the attention paid to
the studies on the Richtmyer–Meshkov instability
(RMI) is focused on the case of shock passage through a
system of gas layers of different densities. The interest
to this problem has been induced, in particular, by multiple
attempts to minimize the process of mixing between the
layers of different densities in targets for inertial confinement
fusion (ICF), caused by excitation of the RMI on the layer
boundaries. The RMI suppression is one of the most important,
but difficult problems in worldwide efforts on ICF. A direct
investigation of this phenomenon in laser experiments (in
NOVA, for example) is a rather difficult task. Shock tubes
are a more promising tool for modeling the impulsively-driven
instabilities in gas layers, for they allow us a detailed
investigation of the mechanism of initiation and the pathways
of evolution of the instability (Jacobs et al.
1995; Aleshin et al. 1995a). A series of shock-tube
experiments for the shock passage through a system of gas
layers of different densities has been carried out. The
effect of a suppression of the RMI has been found. A 2.5-fold
reduction of the mixing region thickness in the presence
of the layer as compared to the thickness without it has
Holographic methods developed to study the behavior
of surfaces shocked by high power lasers are reported.
Shock waves of the order of hundreds of kilobars are generated
in Sn targets 50-μm thick, by a Nd:YAG laser system
with a wavelength of 1.06 μm, a pulse duration of 7.5
ns FWHM, and irradiance in the range (1.0–2.6)·1013
W/cm2. Two configurations of off-axis holography
were applied: holograms based on forward scattering, and
holograms of both backward and forward scattering. The
hologram is produced by scattering of a pulse, 6.7 ns (FWHM),
of green laser light synchronized with the laser that generates
the shock wave. Holograms of the topology of the rear surface
of shocked Sn targets moving in vacuum and in air (at atmospheric
pressure) are reported.
Recently much attention has been paid to multilayer
inertial confinement fusion (ICF) targets, among them the
targets with low-density layers. This allows one to get
a number of interesting results using the presently existing
and future facilities. This concerns the volume absorption
of the laser radiation in a porous matter of the density
higher than the critical plasma density, and the formation
of the radiation absorption region under condition of increasing
geometric opacity of the low-density matter. We consider
the low-density foams, 3D nets, free-standing “snow-like”
layers, and pseudo low-density layers. We use artificial
foam as a convenient model to allow easier comparison of
the experimental laser shot data and the simulation. The
requirements to such layers are also analyzed. The methods
of precision control of the low-density targets are discussed.
High intensity fs-laser pulses can deliver focused intensities
in the region of 1016–1019
W/cm2. If the laser pulse is focused onto a
solid or gaseous material, a plasma is created. The electrons,
as well as the ions are accelerated in the strong laser
field up to energies in the range of keV to several MeV.
The interaction of the high energy particles with cold
material, that is, the solid target yield of intense X-ray
emission, K-shell—as well as bremsstrahlung-radiation.
The K-shell emission from layered targets is a
useful indicator of the production efficiency, energy distribution,
and transport of hot electrons produced in fs-laser plasmas.
For the diagnosis of laser plasma interaction and its application
as an intense X-ray source, the spatial, temporal and spectral
distribution of K-shell X rays is of fundamental
importance. Focusing crystal spectrographs can be used
to obtain a single shot X-ray spectra of laser plasmas
produced by table top fs-lasers. With a spatial- and spectral-focusing
spectrograph based on a toroidally bent crystal, the emission
region of the hot plasma and Kα-radiation
can be determined. Recording the spectra online by a frontside
illuminated charge-coupled device (CCD) allows alignment
of the crystal spectrograph, as well as the laser beam
focusing leading to different X-ray source sizes. Using
a controlled fs-prepulse, an increase in Kα
radiation could be observed with the diagnostic.
Measurements of calibrated high resolution spectra are compared
with particle-in-cell (PIC) calculations of the laser absorption
and hot electron production postprocessed by a Monte–Carlo
(MC) transport model of electron stopping and Kα X-ray
A whole family of laser-plasma interaction experiments
is based on the phase analysis of the laser pulse after
the propagation in a plasma. Typically, this phase is obtained
by means of interferometry. As pulsed interferometry is
a much more difficult task than taking simple images of
the beam, we developed a numerical code for extracting
phase information from images. The technique, based on
the algorithm of Gerchberg–Saxton, showed to be very
effective in retrieving 2D phase distributions of simulated
as well as real beams. The convergence of the algorithm
is fast (some minutes on a personal computer). The electronic
noise in real images is intrinsically discarded by the
Beam smoothing techniques and focused beam profile
control techniques for high efficiency KrF laser fusion
are reported. We have developed 1D and 2D broadband random
phase (BRP) irradiation techniques. Our next idea is the
combination of a laser oscillator with a wide beam divergence
angle and phase plates. The wide divergence angle laser
beam eliminates the speckle patterns caused by the phase
plates. Well characterized focal spot patterns have been
observed with the front-end pulse of the Super-ASHURA KrF
laser system. Amplification experiments are on going.
A diffusion technique most commonly used for filling
targets with a gas fuel. The need to minimize the tritium
inventory in the fill station and to decrease the radiation
damage during the fill raises a question of its thorough
analyses to determine an efficient pressurization scheme
for single and multilayer polymer shells. In this report,
we present the results obtained in this area.
In conventional inertial confinement fusion (ICF),
a high power laser system is used to compress a cryogenic
target and create energy. One of the challenges for ICF
cryogenics is producing the homogeneous and uniform fuel
on the inside surface of a spherical polymer shell. In
this report, we will discuss a conceptual approach based
on freestanding targets and the results of our recent and
Determining the cryogenic target parameters with
high precision calls for the development of a new direction
in the area of target characterization based on microtomography
methods of data processing. In this report we present our
first results in this area.
The project ITEP-TWAC (Tera Watt Accumulator) being
in progress at ITEP (Moscow) requires He-like ions for
non-Liouvillean injection into the storage ring to accumulate
≈2·1013 particles with medium masses
up to 59Co25+. Powerful lasers were
found to be the best choice for those ions production.
This work presents the experimental results of highly charge
ion generation in plasmas produced by the second harmonic
of Nd-glass laser facility with a total energy E
≤ 50 J and pulse duration of about 2.5 ns at GPI (Moscow).
Ti and Ta targets were under investigation. An electrostatic
ion energy analyzer and an ion charge collector were used
to measure the ion charge state spectra at a 3-m distance
from the targets. 5·107 He-like Ti ions
per cm2 within 1 μs pulse as well as 107
Ta+41 per cm2 within 0.8 μs were
The results of numerical simulation of the neutron
generation process in the cone lead targets exposed to
laser irradiation are presented. The experimental time
dependence of the target shell is used as a boundary condition
for the hydrodynamic equations. Deuterium compression is
calculated on the assumption that some part of the shell
that continues to move inward onto the conical target is
decelerated by deuterium in the absence of the reactive
force. The behavior of deuterium is described by the 2D
equations of two temperature gas dynamics with the electron
and ion contributions to the heat conduction taken into
account. The behavior of lead is described by the 2D equations
of gas dynamics closed by the real wide range equation
of state (EOS). The neutron yield in the experiments under
discussion is caused by short duration steep rises of the
ion temperature generated by the collapse of the heading
shock wave and the first reflected one. The stage of adiabatic
compression of the high-temperature plasma was lacking
in the experiment due to the small mass of the shell.
Two series of experiments on laser irradiation
of the different thickness Al-foils were made using laser
facilities “GARPUN” and “PICO”
(Lebedev Physical Institute, Moscow). “GARPUN”
is the KrF-laser with pulse energy Elas
≈ 100 J and pulse duration τ ≈ 100 ns. “PICO”
is a Nd-laser facility. The laser energy is
Elas1 ≈ 20 J and τ ≈
3–4 ns in a single beam. The burn through time
(tb) of different thickness
foils was studied. We have varied the foil thickness:
d = 20–500 μm for “GARPUN”
facility experiments, and d = 3–12 μm
for the case of “PICO” experiments. It was
discovered that the rates of the foil burn through are
much higher than those obtained in (Dahmani et al.,
1991a,b). The experimental data were analyzed with the
help of 2D numerical simulations, using the 2D Euler code
“NUTCY.” Good agreement was obtained between
numerical and experimental results. In the first case the
rate of foil “enlightment” is defined by transversal
displacement of matter (“drilling effect”).
With allowance for the effect of “hot spots formations”
it was possible to explain the burn through of thick foils
and low laser energy at the rear side of films in “PICO”
facility experiments (“microdrilling effect”).
The methods of the diminishing of the influence of microdrilling
effect (or “imprint” effect) on the nonuniformity
of ablation pressure are discussed.