Pulsed Laser Melting of Graphite

1985 ◽  
Vol 51 ◽  
Author(s):  
G. Braunstein ◽  
J. Steinbeck ◽  
M. S. Dresselhaus ◽  
G. Dresselhaus ◽  
B. S. Elman ◽  
...  
Keyword(s):  
Energy Density ◽  
Laser Pulse ◽  
Crystalline Structure ◽  
Pulse Energy ◽  
Laser Pulse Energy ◽  
Pulsed Laser ◽  
Laser Melting ◽  
Liquid Carbon ◽  
Pulse Energy Density ◽  
Ion Implanted

ABSTRACTExperimental evidence for laser melting of graphite, by irradiation with 30ns pulses from a ruby laser, is presented. RBS-channeling analysis, Raman scattering and TEM measurements reveal that the surface of graphite melts at a threshold energy density of about 0.6 J/cm2. For laser pulse energy densities above 0.6 J/cm2, the melt front penetration depth increases nearly linearly with increasing energy density. An intense emission of carbon particles during and after irradiation is observed. The thickness of the carbon layer removed in this process also increases nearly linearly with increasing pulse fluence. A dramatic redistribution of ion implanted impurities is also observed. Furthermore, the crystalline structure of the resolidified material is shown to depend on the energy density of the laser pulse. In order to explain these phenomena, a model for laser melting of graphite at high temperatures to form liquid carbon has been developed in which a free electron gas approximation is used to describe the properties of liquid carbon. The model is solved numerically to give the time and depth dependences of the temperature as a function of the laser pulse energy density. Very good agreement is found between the observed melt depth dependence on laser pulse energy density, as determined by RBS-channeling, and the model calculations. The redistribution of ion implanted impurities and the modification of the crystalline structure, caused by the pulsed laser irradiation, are also consistent with the model and permit the determination, for the first time, of interfacial segregation coefficients for impurities in liquid carbon. The model also predicts that liquid carbon at low pressure (p < 1 kbar) has metallic properties.

scholarly journals Спектральные характеристики свечения поверхности частиц каменных углей во время воздействия лазерных импульсов в режиме свободной генерации

2020 ◽  
Vol 128 (12) ◽  
pp. 1898
Author(s):  
Б.П. Адуев ◽  
Д.Р. Нурмухаметов ◽  
Я.В. Крафт ◽  
З.P. Исмагилов
Keyword(s):  
Energy Density ◽  
Laser Pulse ◽  
Pulse Energy ◽  
Laser Pulse Energy ◽  
Emission Spectra ◽  
Radiation Energy ◽  
Laser Pulses ◽  
Radiation Energy Density ◽  
Pulse Energy Density ◽  
Coal Particles

In this work, we investigated the glow spectra of coal fractions with dimensions 63 μm directly during the action of neodymium laser pulses (120 μs). Depending on the radiation energy density H, the emission spectra have a different character. The glow at the minimum values ​​of the laser pulse energy density Hcr (1) is associated with the ignition of small coal particles (~ 1 μm) present in the fractions and the ignition of reactive microprotrusions on the surface of the larger coal particles. The glow spectra at this stage are of a non-thermal nature and are associated with the emission of molecules of volatile substances in the gas phase and the products of their oxidation. With an increase in the laser pulse energy density H, a thermal glow of the surface of larger coal particles is observed, which is described by the Planck formula at T = 3100 K. When H = Hcr (2) is reached, the surface of the coal particles is ignited during the action of the laser pulse. Contributions to the spectra are the glow of the surface of coal particles, emitted carbon particles, and the glow associated with the emission of excited molecules H2, H2O, CO2. With an increase in H> Hcr (2), the processes leading to the glow of coal particles during a laser pulse are similar to those described above for Hcr (2), but the glow intensity increases

The influence of nanosecond laser pulse energy density for paint removal

Optik ◽  
2018 ◽  
Vol 156 ◽  
pp. 841-846 ◽  
Author(s):  
Xiaokui Li ◽  
Qiuhui Zhang ◽  
Xinzhi Zhou ◽  
Daoqiang Zhu ◽  
Quanxi Liu
Keyword(s):  
Energy Density ◽  
Laser Pulse ◽  
Pulse Energy ◽  
Laser Pulse Energy ◽  
Nanosecond Laser Pulse ◽  
Nanosecond Laser ◽  
Pulse Energy Density ◽  
Paint Removal

Bilayer Structures Obtained by Pulsed Laser Quenching of Binary Systems

1988 ◽  
Vol 100 ◽  
Author(s):  
P. Baeri ◽  
G. Foti ◽  
M. G. Grimaldi ◽  
F. Priolo ◽  
R. Reitano ◽  
...  
Keyword(s):  
Energy Density ◽  
Laser Pulse ◽  
Binary Systems ◽  
Pulsed Laser ◽  
Epitaxial Layers ◽  
Silicon Substrates ◽  
High Fluence ◽  
Laser Quenching ◽  
Ion Implanted

ABSTRACTNiSi and Ni2Si layers on silicon substrates as well as high fluence Si(As) ion implanted layers,have been rapidly melted by 30 ns Nd laser pulse irradiation.The energy density ranged between 0.4 and 1.2 J/cm2. Bilayer structures have been observed when the energy density has been chosen properly.Buried epitaxial layers together with an amorphous or a policrystalline layer on top,have been detected by RBS and TEM measurements.

Femtosecond and Nanosecond Laser Pulse Crystallization of Thin a-Si:H Films on Non-Refractory Glass Substrates

2007 ◽  
Vol 131-133 ◽  
pp. 479-484 ◽  
Author(s):  
Vladimir A. Volodin ◽  
M.D. Efremov ◽  
G.A. Kachurin ◽  
S.A. Kochubei ◽  
A.G. Cherkov ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Energy Density ◽  
Laser Pulse ◽  
Raman Scattering ◽  
Pulse Energy ◽  
Laser Wavelength ◽  
Nanosecond Laser ◽  
Glass Substrates ◽  
Pulse Energy Density ◽  
Krf Laser

Thin (90 nm) a-Si:H films on Corning 7059 glass substrates have been crystallized by 120 fs pulses of Ti:sapphire and nanosecond pulse XeCl and KrF excimer lasers. Initial films were deposited using low-temperature plasma enhanced deposition technique. The structural properties of the films were characterized using the spectroscopy of Raman scattering, excited by the argon laser (line 514.5 nm) and using electron microscopy. For the femtosecond pulse treatments the ablation threshold was found to be some more than 65 mJ/cm2. When pulse energy density was lower than ~30 mJ/cm2 no structural changes were observed. In optimal regimes the films were found to be fully crystallized with needle grain structure, according to the Raman scattering and electron microscopy data. Estimates show the pulse energy density was lower than the Si melting threshold, so non-thermal “explosive” impacts may play some role. The main result in nanosecond XeCl and KrF laser pulse crystallization is the narrower window between beginning of crystallization and ablation for KrF laser (wavelength 248 nm) than for the XeCl laser (wavelength 308 nm). So, the possibility of the femtosecond and nanosecond laser pulses to crystallize a-Si films on non refractory glass substrates was shown. The results obtained are of great importance for manufacturing of polycrystalline silicon layers on non-refractory large-scale substrates for giant microelectronics.

A Model Ni–Al–Mo Superalloy Studied by Ultraviolet Pulsed-Laser-Assisted Local-Electrode Atom-Probe Tomography

2015 ◽  
Vol 21 (2) ◽  
pp. 480-490 ◽  
Author(s):  
Yiyou Tu ◽  
Elizaveta Y. Plotnikov ◽  
David N. Seidman
Keyword(s):  
Laser Pulse ◽  
Charge State ◽  
Pulse Energy ◽  
Atom Probe Tomography ◽  
Laser Pulse Energy ◽  
Pulsed Laser ◽  
Atom Probe ◽  
Resolving Power ◽  
Full Width ◽  
Experimental Conditions

AbstractThis study investigates the effects of the charge-state ratio of evaporated ions on the accuracy of local-electrode atom-probe (LEAP) tomographic compositional and structural analyses, which employs a picosecond ultraviolet pulsed laser. Experimental results demonstrate that the charge-state ratio is a better indicator of the best atom-probe tomography (APT) experimental conditions compared with laser pulse energy. The thermal tails in the mass spectra decrease significantly, and the mass resolving power (m/Δm) increases by 87.5 and 185.7% at full-width half-maximum and full-width tenth-maximum, respectively, as the laser pulse energy is increased from 5 to 30 pJ/pulse. The measured composition of this alloy depends on the charge-state ratio of the evaporated ions, and the most accurate composition is obtained when Ni2+/Ni+ is in the range of 0.3–20. The γ(f.c.c.)/γ'(L12) interface is quantitatively more diffuse when determined from the measured concentration profiles for higher laser pulse energies. Conclusions of the APT compositional and structural analyses utilizing the same suitable charge-state ratio are more comparable than those collected with the same laser pulse energy.

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