scholarly journals Shock pressure induced by 0.44 μm laser radiation on aluminum targets

2003 ◽  
Vol 21 (4) ◽  
pp. 481-487 ◽  
Author(s):  
D. BATANI ◽  
H. STABILE ◽  
A. RAVASIO ◽  
T. DESAI ◽  
G. LUCCHINI ◽  
...  
Keyword(s):  
Laser Radiation ◽  
Laser Intensity ◽  
Streak Camera ◽  
Present Report ◽  
Target Thickness ◽  
Shock Velocity ◽  
Shock Pressure ◽  
Phase Zone ◽  
Laser Absorption ◽  
Good Agreement

Shock pressure generated in aluminum targets due to the interaction of 0.44 μm (3 ω of iodine laser) laser radiation has been studied. The laser intensity profile was smoothed using phase zone plates. Aluminum step targets were irradiated at an intensity I ≈ 1014 W/cm2. Shock velocity in the aluminum target was estimated by detecting the shock luminosity from the target rear using a streak camera to infer the shock pressure. Experimental results show a good agreement with the theoretical model based on the delocalized laser absorption approximation. In the present report, we explicitly discuss the importance of target thickness on the shock pressure scaling.

A model for the relation between respiratory neural and mechanical outputs. III. Validation

1981 ◽  
Vol 51 (4) ◽  
pp. 990-1001 ◽  
Author(s):  
M. Younes ◽  
W. Riddle ◽  
J. Polacheck
Keyword(s):  
Respiratory System ◽  
Pressure Wave ◽  
Time Course ◽  
Present Report ◽  
Occlusion Pressure ◽  
Single Breath ◽  
Wave Forms ◽  
Inspiratory Activity ◽  
Good Agreement

In the preceding two communications we described a model for the relation between respiratory neural and mechanical outputs. In the present report we test the accuracy of the model in predicting volume and flow from occlusion pressure wave forms, and vice versa. We performed single-breath airway occlusions in 21 unconscious subjects and determined the time course of occlusion pressure. We also measured the passive properties of the respiratory system. The time course of volume and flow was predicted from the occlusion pressure wave forms, and the results were compared with the spontaneous breaths immediately preceding occlusion. Inspiratory duration, shape and amplitude of occlusion-pressure wave forms, and the passive properties of the respiratory system varied widely among subjects. There was good agreement between predicted and observed values in all cases. Except for some prolongation of inspiration (Hering-Breuer reflex), diaphragmatic activity did not change during occlusion. Since occlusion pressure is proportional to inspiratory activity, we conclude that the model described provides a good approximation of the relation between inspiratory activity and spirometric output.

scholarly journals Shock impedance matching experiments in foam-solid targets and implications for “foam buffered ICF”

1999 ◽  
Vol 17 (3) ◽  
pp. 529-535 ◽  
Author(s):  
W. NAZAROV ◽  
D. BATANI ◽  
A. MASINI ◽  
A. BENUZZI ◽  
M. KOENIG ◽  
...  
Keyword(s):  
Streak Camera ◽  
Second Harmonic ◽  
Impedance Matching ◽  
Max Planck ◽  
Phase Zone ◽  
Third Harmonic ◽  
Shock Impedance ◽  
Al Foam ◽  
Pulse Energies ◽  
Mismatch Effect

We studied the influence of foams on laser produced shocks. Experiments were performed at LULI using a Nd laser converted to second harmonic, and at MPQ (Max Planck Institut für Quantenoptik) using the iodine Asterix laser converted to third harmonic. In both cases, sub-ns lasers with pulse energies of several tens of joules were focused on large focal spots (hundreds of microns) to reduce 2D effects. The laser beams were optically smoothed with phase zone plates (PZP) and directly focused on layered targets made of a foam layer on the laser side and a stepped Al layer on the other side. A visible streak camera was used to detect shock breakthrough at the base and at the step of the Al target, allowing shock velocity to be determined. Using the well known SESAME Al equation of state, we determined shock pressure. A stronger pressure increase was measured when foam was present, compared to what was obtained by focusing the laser beam directly on the Al target. This was due to the impedance mismatch effect at the Al-foam interface.

scholarly journals Generation of hot and dense plasmas in laser accelerated colliding foil systems

1998 ◽  
Vol 16 (1) ◽  
pp. 21-30 ◽  
Author(s):  
P. Angelo ◽  
H. Derfoul ◽  
P. Gauthier ◽  
P. Sauvan ◽  
A. Poquerusse ◽  
...  
Keyword(s):  
Thermal Conduction ◽  
Focal Spot ◽  
Laser Intensity ◽  
Dense Plasma ◽  
Lateral Expansion ◽  
Dense Plasmas ◽  
Monochromatic Imaging ◽  
Thin Foils ◽  
Plasma Effects ◽  
Good Agreement

We create hot (Te > 200 eV) and dense (Ne > 1023 cm−3) plasmas in the colliding zone of two thin foils accelerated by two laser beams of the LULI facilities. Three spectroscopic diagnostics (two 1D space-resolved spectrographs and a 2D monochromatic imaging) are used to drive the efficiency of the compression. We show that 2D effects are important. Realistic simulations of these experiments must be done, taking into account the inhomogeneity of the laser intensity in the focal spot, the foil distorsion, the plasma lateral expansion, and the lateral thermal conduction. Two-dimensional LASNEX code results are in good agreement with our experimental results. The optimized compressed plasmas generated are favorable for the exhibition of dense plasma effects due to molecular formations, and they reproduce in laboratory some astrophysical situations.

Massive Parallel Laser Shock Peening: Simulation, Verification, and Analysis

2005 ◽  
Author(s):  
A. W. Warren ◽  
Y. B. Guo ◽  
S. C. Chen
Keyword(s):  
Residual Stress ◽  
Surface Integrity ◽  
Compressive Residual Stress ◽  
Laser Intensity ◽  
Shock Pressure ◽  
Laser Shock Peening ◽  
Massively Parallel ◽  
Laser Shock ◽  
Laser Material ◽  
Shock Peening

Laser shock peening (LSP) is a surface treatment process to improve the surface integrity of metallic components. The nearly pure mechanical process of LSP results in favorable surface integrity such as compressive residual stress and improved surface material properties. Since LSP is a transient process with laser pulse duration time on the order of 40 ns, real time in-situ measurement of laser/material interaction is very challenging, if not impossible. A fundamental understanding of laser/material interactions is essential for LSP planning. Previous finite element simulations of LSP have been limited to a single laser shock location for both two and three dimensional modeling. However, actual LSP are performed in a massively parallel mode which involves almost simultaneous multi-laser/material interactions in order to induce uniform compressive residual stress across the entire surface of the workpiece. The massively parallel laser/material interactions have a significant compound/interfering effect on the resulting surface integrity of the workpiece. The numerical simulation of shock pressure as a function of time and space during LSP is another critical problem. The purpose of this paper is to investigate the effects of parallel multiple laser/material interactions on the stress/strain distributions in the workpiece during LSP of AISI 52100 steel. FEA simulations of LSP in single and multiple passes were performed with the developed spatial and temporal shock pressure model via a subroutine. The simulated residual stresses agree with the measured data in nature and trend, while magnitude can be influenced by the interactions between neighboring peening zones and the locations of residual stress measurement. Design-of-experiment (DOE) based simulations of massive parallel LSP were also performed to determine the effects of laser intensity, laser spot size, and peening spacing on stresses and strains. Increasing the laser intensity increases both the stress magnitude and affected depth. The use of smaller laser spot sizes decreases the largest magnitude of residual stress and also decreases the depth affected by LSP. Larger spot sizes have less energy attenuation and cause more plastic deformation. Spacing between peening zones is critical for the uniformity of mechanical properties across the surface. The greatest uniformity and largest stress magnitudes are achieved by overlapping of the laser spots.

CO2 Laser Measurements on Shock Fronts

1974 ◽  
Vol 52 (21) ◽  
pp. 2083-2087 ◽  
Author(s):  
A. R. Strilchuk ◽  
A. A. Offenberger
Keyword(s):  
Co2 Laser ◽  
Atmospheric Pressure ◽  
Low Pressure ◽  
Shock Velocity ◽  
Piezoelectric Transducers ◽  
Angle Of Incidence ◽  
Laser Measurements ◽  
Heterodyne Technique ◽  
Shock Fronts ◽  
Good Agreement

CO2 laser measurements on reflectivity of shock fronts in N2, Ar, and CO2 at atmospheric pressure and N2 at low pressure are presented as well as results of shock velocity determination using a heterodyne technique. The measured and expected variation of reflectivity with angle of incidence show good agreement as do velocities compared with those determined using piezoelectric transducers.

scholarly journals Simulation of femtosecond laser absorption by metallic targets and their thermal evolution

2017 ◽  
Vol 35 (3) ◽  
pp. 415-428 ◽  
Author(s):  
A. Suslova ◽  
A. Hassanein
Keyword(s):  
Femtosecond Laser ◽  
Laser Intensity ◽  
Laser Energy ◽  
Absorption Efficiency ◽  
Optical Parameters ◽  
Temperature Dependent ◽  
Simulation Code ◽  
Laser Absorption ◽  
Plasma State ◽  
Wide Range

AbstractThe interaction of femtosecond laser with initially cold solid metallic targets (Al, Au, Cu, Mo, Ni) was investigated in a wide range of laser intensity with focus on the laser energy absorption efficiency. Our developed simulation code (FEMTO-2D) is based on two-temperature model in two-dimensional configuration, where the temperature-dependent optical and thermodynamic properties of the target material were considered. The role of the collisional processes in the ultrashort pulse laser–matter interaction has been carefully analyzed throughout the process of material transition from the cold solid state into the dense plasma state during the pulse. We have compared the simulation predictions of the laser pulse absorption with temperature-dependent reflectivity and optical penetration depth to the case of constant optical parameters. By considering the effect of the temporal and spatial (radial) distribution of the laser intensity on the light absorption efficiency, we obtained a good agreement between the simulated results and available experimental data. The appropriate model for temperature-dependent optical parameters defining the laser absorption efficiency will allow more accurate simulation of the target thermal response in the applications where it is critical, such as prediction of the material damage threshold, laser ablation threshold, and the ablation profile.

scholarly journals Ion energy enhancement from TNSA plasmas obtained from advanced targets

2014 ◽  
Vol 32 (3) ◽  
pp. 383-389 ◽  
Author(s):  
L. Torrisi
Keyword(s):  
Electric Field ◽  
Double Layer ◽  
Laser Intensity ◽  
Laser Wavelength ◽  
Rear Side ◽  
Energetic Ions ◽  
Ion Energy ◽  
Fast Electrons ◽  
Surface Reflection ◽  
Laser Absorption

AbstractLaser generated plasmas from target normal sheath acceleration produce energetic ions from the rear side of the target due to the formation of a high directive electric field. Fast electrons are ejected from the rear side of the target and a successive Coulomb explosion is driven by the fast electrons generating a high electric field of double layer. The ion acceleration is mainly controlled by the laser intensity and by the square of the laser wavelength. Literature reports that at intensities of the order of 1018 W/cm2 and at wavelengths of about 1 µm the ion energy is of the order of 5 MeV/nucleon. The use of advanced targets realized with the aim to reduce the surface reflection, to increase the laser absorption coefficient and, with an optimal thickness, to increase the electric field of the double layer, permits to enhance the ion energy acceleration, so that the energy of 5.0 MeV per charge state can be reached at about 1016 W/cm2, as it will be presented and discussed.

scholarly journals X-ray emission by the rear side of laser-irradiated gold targets

1991 ◽  
Vol 9 (2) ◽  
pp. 527-540 ◽  
Author(s):  
D. Babonneau ◽  
J. L. Bocher ◽  
C. Bayer ◽  
A. Decoster ◽  
D. Juraszek ◽  
...  
Keyword(s):  
Energy Balance ◽  
Streak Camera ◽  
Thermal Flux ◽  
Rear Side ◽  
Time Resolved ◽  
X Ray ◽  
Transmission Grating ◽  
Flux Limiter ◽  
Conversion Efficiencies ◽  
Good Agreement

We present results of X-ray emission by the rear side of gold thin targets irradiated by the Phebus laser at λ = 0.35 μm, τ = 0.7 and 1.3 ns, and EL = 1.5 kJ. A streak camera coupled with a transmission grating gave the time-resolved X-ray emission of the rear side. Also, a streak camera coupled with a slit allowed us to obtain information about the space and time evolution of the plasma. Some other diagnostics gave information about the energy balance and the X-ray conversion efficiency. The results are in good agreement with previous ones obtained with the Octal laser, particularly on optimum thicknesses for X-ray conversion efficiencies. Values of the thermal flux limiter are deduced. Simulations with FCI 1 code with multigroup radiative transfer and non-LTE ionization reproduce the experimental results only about some points. A number of reasons, such as 2-D effects and problems of opacity, are invoked.

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