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Starting from the same initial structure, solid-hydrogen shells were dynamically compressed at different implosion velocities by performing large-scale molecular dynamic simulations to explore their microscopic evolution under the ultrafast dynamic compression. The ultrafast dynamic compression is revealed to prohibit the solid shell from the structural phase transition, while the phase transition is first initiated at the inner surface of the shell. A faster compression generates a higher pressure in the shell at a given convergence ratio by preventing the hydrogen atoms from ejecting out of the solid-hydrogen shell to release pressure. These results provide a glimpse of the microscopic scenario of the solid-hydrogen shell at early times during the ultrafast dynamic compression, suggesting that the implosion velocity must be carefully determined to mitigate the growth of hydrodynamic instabilities on the inner surface of the solid-hydrogen shell. [ABSTRACT FROM AUTHOR]

Mbar-level ablative plume pressures, produced by single-shot femtosecond laser ablation of a dry Ti alloy surface and driving shock waves in air and in the solid target, were characterized using non-contact broad-band ultrasonic measurements. X-ray diffraction measurements reveal the resulting shock-wave induced sub-GPa residual compressive stresses over multi-micrometer depths inside the target, indicating GPa-level residual compressive stresses on its surface. [ABSTRACT FROM AUTHOR]

Silicon (Si) and Germanium (Ge) can be used as the dopant in the ablator material for the purpose of reducing preheating in indirect-drive inertial confinement fusion. Their performances in reducing preheating are quite different. A method to evaluate the difference of these two kinds of dopants has been presented in this letter. In the Shenguang-II high power laser facility, the M-band (1.6-4.4 keV) transmission flux of Si-coated plastic (CH) and Ge-coated plastic (CH) has been measured by using the M-band x-ray diode. In the experiment, we find that the Si-coated CH can absorb more M-band x-rays and thus reduce the preheating of the fuel in our experiment condition. By using the radiation hydrodynamic code MULTI-1D, we got the simulation result which was well suited for the experiment. The comparison of their opacities (Te = 60-100 eV and q = 0:1-0:5g/cm³) also shows that the opacity of Si is higher than that of Ge almost in the whole range of 1.6-4.4 keV. [ABSTRACT FROM AUTHOR]

Electron density was measured by Stark broadening in an ablative pulsed plasma thruster. The asymmetrical deconvolution is used to obtain Stark broadening. The result shows that the electron density in the discharge channel is 2.534×1022 m-3 when the discharge energy is 5 J and the measured electron temperature is 18 000 K, and it is in excellent agreement with other experimental and theoretical data. The electron density in the discharge channel increases very minimally with increasing discharge energy. [ABSTRACT FROM AUTHOR]

This letter reports observation of ablated holes as small as 0.7 μm fabricated by single 25 ns pulses of KrF (λ=248 nm) laser focused onto a 5.6 μm spot. Samples with high thermal conductivity films with respect to that of the substrate (Si/silica, Al/glass) repeatedly showed considerable reduction in the size of the ablated spot (0.7- and 1.2-μm-diam holes, respectively). This letter also presents a likely mechanism of the observed super-resolution and the criteria necessary to achieve super-resolution. Due to the nonoptical origin of this effect it is expected that a tightly focused (<0.5 μm) laser beam can be used to ablate with nanoscale (<100 nm) resolution. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Conditions for ablation of materials and film deposition were analyzed for a pulsed (∼100 ns) electron beam produced by a channel-spark source. For dielectric materials, we found the existence of an optimal source voltage related to the saturation of the pulse current. Our analysis indicates a larger ablated mass, smaller optimal deposition rates (∼0.25 Å/pulse), and a larger optimal target to substrate distance relative to pulsed laser deposition process. [ABSTRACT FROM AUTHOR]

Short pulses of far-ultraviolet (193 nm) laser radiation are capable of etching organic polymer films without melting the remaining sample. The mechanism proposed for this ablative photodecomposition attributes ablation to the increase in volume that accompanies the photolysis of the polymer. A model of the microscopic process is presented here. The predictions of the model include ablation without melting, a mean perpendicular ejection velocity of 1300 m/s, and an angular distribution of the ablated material which has a narrow peak normal to the surface. [ABSTRACT FROM AUTHOR]

Measurements of the total energy carried by fast ablator-ions in direct-drive implosions on OMEGA have been conducted using magnetic and Thomson Parabola spectrometers. It is shown that the total laser energy lost to fast ablator-ions for plastic and glass targets is comparable and that it is a modest fraction of the incident laser energy (<=1%). These measurements have been used to infer a non-linear, voltage-dependent target capacitance (∼0.1 nF) associated with the space-charge that accelerates the fast-ions. [ABSTRACT FROM AUTHOR]

We present a laser induced ablation process to fabricate ultrathin graphitic flakes. By varying the fluence of the ablating pulsed fs-laser radiation, we identify distinct values for "thermal" evaporation and so-called "non-thermal" ablation of graphitic flakes. The presence of the non-thermal ablation is a direct consequence of the strong asymmetry of the bonding strength in normal and in-plane direction in layered materials, such as graphite. The experimentally extracted non-thermal ablation threshold for graphite of 250 mJ/cm2 agrees well with theoretical predictions. Finally, we deposited ultrathin graphitic flakes of 50 μm2 in size, which we characterize by Raman spectroscopy and scanning force microscopy. [ABSTRACT FROM AUTHOR]