scholarly journals Asymptotic measurements of free surface instabilities in laser-induced shock waves

1996 ◽  
Vol 14 (2) ◽  
pp. 133-147 ◽  
Author(s):  
M. Werdiger ◽  
B. Arad ◽  
Z. Henis ◽  
Y. Horowitz ◽  
E. Moshe ◽  
...  
Keyword(s):  
Free Surface ◽  
Shock Waves ◽  
Pulse Width ◽  
Laser System ◽  
Optical Scattering ◽  
Liquid Transition ◽  
Aluminium Copper ◽  
Metallic Sample ◽  
Mass Ejection ◽  
Surface Occurrence

An experimental technique based on optical scattering to detect melting in release of strongly shocked materials is presented. This method is used to study the asymptotic behavior of the free surface of shock-loaded materials. After reflection of a shock wave from a metallic sample free surface, occurrence of a solid to liquid transition will induce a dynamic behavior such as mass ejection and development of instabilities. A study of the mass ejection due to laser-induced shock waves in aluminium, copper, and tin targets is presented. Shock waves of order of hundreds of kilobars to more than one megabar are produced by a Nd:YAG laser system with a wavelength of 1.06 μm, pulse width of 7 ns FWHM focused to spot of 200 μm. The velocities, size, and topological structure of the ejected particles are measured. The radii of the ejecta are in the range 0.5–7 μm.

scholarly journals Detecting of melting by changes of rear surface reflectivity in shocked compressed metals using an interferometric diagnostic method

1999 ◽  
Vol 17 (3) ◽  
pp. 547-556 ◽  
Author(s):  
M. WERDIGER ◽  
S. ELIEZER ◽  
S. MAMAN ◽  
Y. HOROVITZ ◽  
E. MOSHE ◽  
...  
Keyword(s):  
Shock Wave ◽  
Free Surface ◽  
Pulse Width ◽  
Diagnostic Method ◽  
Laser System ◽  
Rear Surface ◽  
Power Laser ◽  
Shock Wave Pressure ◽  
Surface Reflectivity ◽  
Pressure Regime

When a high power laser (1012 W/cm2) irradiates a target, it induces a shock wave, which reaches the (free) rear surface. The free surface is accelerated and the shock wave is back-reflected as a rarefaction wave. In the shock wave pressure regime involved here, melting of the target during the shock or during the rarefaction may occur. An optically recording velocity interferometric system (ORVIS) has been developed to measure the time evolution of the change in the reflectivity of the free surface. Shock waves of the order of hundreds of kilobars are produced in 50–125 μm thick Sn and Al foils, by a Nd:YAG laser system with a wavelength of 1.06 μm, pulse width of 7 ns (FWHM), and irradiance in the range (1.4–2.4)·1013 W/cm2. The changes in the reflectivity occur along two time scales: a slow one, more than 17 ns in Al and more than 30 ns in Sn, and a rapid one, less than 2.5 ns, in both materials. A possible explanation for the sharp decreases in the time scale is that melting occurs during the release of the free surface.

scholarly journals Development of holographic methods for investigating a moving free surface, accelerated by laser-induced shock waves

1999 ◽  
Vol 17 (4) ◽  
pp. 653-660 ◽  
Author(s):  
M. WERDIGER ◽  
S. ELIEZER ◽  
S. MAMAN ◽  
Y. HOROVITZ ◽  
B. ARAD ◽  
...  
Keyword(s):  
Shock Wave ◽  
Free Surface ◽  
Shock Waves ◽  
Atmospheric Pressure ◽  
Laser Light ◽  
Laser System ◽  
Rear Surface ◽  
Green Laser ◽  
Forward Scattering ◽  
High Power Lasers

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.

scholarly journals Scanning electron microscope studies on laser ablation of solids

2019 ◽  
Vol 37 (01) ◽  
pp. 101-109 ◽  
Author(s):  
Mohamed E. Shaheen ◽  
Joel E. Gagnon ◽  
Brian J. Fryer
Keyword(s):  
Pulse Width ◽  
Laser Energy ◽  
Laser System ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Ablation Rate ◽  
Laser Wavelength ◽  
High Laser Fluence ◽  
Electron Imaging ◽  
Scanning Electron

AbstractThis study investigates the interaction of picosecond laser pulses with sapphire and brass in air using scanning electron microscopy. A picosecond laser system operating at a wavelength of 785 nm, pulse width of 110 ps, and variable repetition rate (1–1000 Hz) was used in this study. The pulse width applied in this work was not widely investigated as it lies in the gap between ultrashort (femtosecond) and long (nanosecond) pulse width lasers. Different surface morphologies were identified using secondary electron and backscattered electron imaging of the ablated material. Thermal ablation effects were more dominant in brass than in sapphire. Exfoliation and fractures of sapphire were observed at high laser fluence. Compared with brass, multiple laser pulses were necessary to initiate ablation in sapphire due to its poor absorption to the incident laser wavelength. Ablation rate of sapphire was lower than that of brass due to the dissipation of a portion of the laser energy due to heating and fracturing of the surface.

Detection of coronal mass ejection associated shock waves in the outer corona

2000 ◽  
Vol 105 (A3) ◽  
pp. 5081-5092 ◽  
Author(s):  
N. R. Sheeley ◽  
W. N. Hakala ◽  
Y.-M. Wang
Keyword(s):  
Shock Waves ◽  
Coronal Mass Ejection ◽  
Outer Corona ◽  
Mass Ejection

scholarly journals Shock Wave Interactions with Viscosity Observed after the Coronal Mass Ejection Activities Occurred on December 18, 1999 and April 4, 2001

2018 ◽  
pp. 1-11
Author(s):  
Huseyin Cavus ◽  
Aysel Ibrahim Karafistan
Keyword(s):  
Shock Waves ◽  
Geomagnetic Storms ◽  
Magnetic Activity ◽  
Wave Interactions ◽  
Major Objective ◽  
Subsonic Regime ◽  
Interaction Of Shock Waves ◽  
Shock Wave Interactions ◽  
Solar Magnetic Activity ◽  
Mass Ejection

The release of magnetic field and plasma from the solar atmosphere (i.e. coronal mass ejections-CMEs and solar wind) resulting from solar magnetic activity can produce shock waves and geomagnetic storms. Shock waves are known to occur while the solar ejected particles alter from the supersonic to the subsonic regime. Especially, in the supersonic case for the flow of compressible gas interaction of shock waves with viscosity plays a key role for space weather broadcasts. Therefore, the major objective of this paper was to search the outcome of viscosity in the shocks subsequently detected after the CMEs occurred on December 18, 1999 and April 4, 2001 by using the previous modelling study of [1].  

scholarly journals Femtosecond Laser Machining At Submicron And Nano Scale

2021 ◽  
Author(s):  
Alireza Dalili
Keyword(s):  
Femtosecond Laser ◽  
Pulse Energy ◽  
Repetition Rate ◽  
Pulse Width ◽  
Laser System ◽  
High Repetition Rate ◽  
Silicon Wafers ◽  
Good Precision ◽  
High Repetition ◽  
Nano Scale

The arrival of the femtosecond laser with a MHz repetition rate has provided the industry with a new tool to conduct submicron and nano scale machining. Several advantages such as high quality machining finish, good precision and high throughput can be obtained when using femtosecond laser to conduct nanomachining over lithography techniques currently in use. High repetition rate systems are preferred over low repetition rate femtosecond laser systems that have been studied by others due to their increased stability, speed, quality and discovery of new phenomena such as ripples and grains. This thesis proposes a high repetition rate fiber femtosecond laser system for meeting the above-mentioned conditions. The influence of the laser repetition rate and pulse energy on the size and quality of nano features fabricated on silicon wafers was investigated. Higher repetition rates led to smaller cutlines with uniform width. A 110 nm crater with a small heat affected zone of 0.79 µm was obtained at 13 MHz repetition rate and 2.042 J/cm² energy fluence. In terms of nanomachining below the ablation threshold (surface patterning), the influence of pulse width, repetition rate and pulse energy on the spacing of ripples, as well as diameter of grains created on silicon wafers, was examined. For the pulse width, repetition rate and pulse energy range used, the ripple spacing and grain diameter increased with laser pulse duration while other parameters did not play a significant role. These results show the capability of the proposed system in meeting the industry requirements.

scholarly journals Numerical Analysis of Free Surface Shock Waves around Bow by Modified MAC-Method

1981 ◽  
Vol 1981 (150) ◽  
pp. 1-8 ◽  
Author(s):  
Akira Suzuki ◽  
Hideaki Miyata ◽  
Hisashi Kajitani ◽  
Makoto Kanai
Keyword(s):  
Free Surface ◽  
Numerical Analysis ◽  
Shock Waves ◽  
Mac Method

The Effects of Near Surface and Bulk Microstructure on Lithium Intercalation of Disordered, “Hard” Carbons

1997 ◽  
Vol 496 ◽  
Author(s):  
William R. Even ◽  
Lawrence W. Peng ◽  
Nancy Yang ◽  
Ronald Guidotti ◽  
Thomas Headley
Keyword(s):  
Free Surface ◽  
Surface Reconstruction ◽  
Pulse Width ◽  
Loss Rate ◽  
Average Power ◽  
Rate Capability ◽  
Irreversible Loss ◽  
Near Surface ◽  
Surface Ordering ◽  
Bulk Structure

ABSTRACTDisordered carbons were synthesized at 700°C from methacrylonitrile-divinylbenzene precursors. The disorder, even at the free surface, was confirmed with TAM. These powdered carbons were subjected to rapid surface heating by a pulsed infrared laser. While the bulk structure remained essentially unchanged, there was substantial surface reconstruction to a depth of 0.25μm after heating (5.9 W average power at 10Hz, 10 ns pulse width, 1064nm wavelength). The surface ordering appears similar to the bulk microstructure of carbons isothermally annealed at 2,200°C (i.e., turbostratic). Improvements were observed in first cycle irreversible loss, rate capability, and coulombic efficiencies of the reconstructed carbons, relative to the untreated carbon.

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