Heat Treatment of the Surface of the ChS57 Alloy with Powerful Nanosecond Ultraviolet Laser Pulses

The threshold of optical breakdown of the nickel alloy ChS57 (Inconel) was measured at a wavelength of 0.355 μm with a laser pulse duration of 10 ns. Heat treatment of ChS57 above pulse energy density threshold (1 - 2.5 J/cm2) occurred mainly in the ablative mode with almost no melting. The elemental composition of the surface layer did not change at an irradiation in a fixed spot. When a laser beam moves along the surface of the sample at a speed of 1 mm / s and at pulse energy density of about 0.02 J/cm2, oxygen was detected in the elemental composition (3 – 4 wt. %). However, the proportions of the elemental composition of the alloy remained virtually unchanged. Heat treatment under threshold at pulse energy density ≥ 0.25 J/cm2 revealed a rise of the surface layer with traces of high-temperature plastic deformation in the form of slippage on grain boundaries and crystallographic slip.

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

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

Monitoring the Sky with the Prototype All-Sky Imager on the LWA1

We present a description of the Prototype All-Sky Imager (PASI), a backend correlator and imager of the first station of the Long Wavelength Array (LWA1). PASI cross-correlates a live stream of 260 dual-polarization dipole antennas of the LWA1, creates all-sky images, and uploads them to the LWA-TV website in near real time. PASI has recorded over 13,000[Formula: see text]hr of all-sky images at frequencies between 10 and 88[Formula: see text]MHz creating opportunities for new research and discoveries. We also report rate density and pulse energy density limits on transients at 38, 52, and 74[Formula: see text]MHz, for pulse widths of 5[Formula: see text]s. We limit transients at those frequencies with pulse energy densities of [Formula: see text][Formula: see text][Formula: see text], [Formula: see text][Formula: see text][Formula: see text], and [Formula: see text][Formula: see text][Formula: see text][Formula: see text]J[Formula: see text]m[Formula: see text][Formula: see text]Hz[Formula: see text] to have rate densities [Formula: see text][Formula: see text][Formula: see text], [Formula: see text][Formula: see text][Formula: see text], and [Formula: see text][Formula: see text][Formula: see text] year[Formula: see text].

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

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.

Simulation Of Polycrystalline Silicon Growth By Pulsed Excimer Laser Annealing

The dynamic simulation of poly-Si film synthesis has been fulfilled by means of the overlapping irradiation of single- and double-pulsed XeCl excimer lasers shaped into the line beam. A novel model applied to the dynamic simulation is based on the homogeneous nucleation, and the growth and shrinkage velocity of Si grains. The results simulated with the single-pulsed XeCl excimer laser has reproduced the super lateral growth (SLG) phenomenon which occurs in the very narrow range of energy density (the near complete melt regime). The actual energy density dispersion within 5.3% allows us to visualize the multiformity of grain sizes in the cross sectional texture. Standing on the reproduction of the SLG phenomenon by the single-pulsed irradiation, we have obtained the practical knowledge of the growth process of larger grains by the double-pulsed irradiation. We intend that the first pulse has charge of completely melting and the second pulse has charge of adjusting the number of nuclei. The adjustment of the first pulse energy density rather than that of the second pulse energy density leads to the growth of huge columnar grains much larger than the thickness of the Si layer. For the double-pulsed irradiation, the influence of the worst energy density dispersion (each of double pulses has the same fluctuation as the single pulse) is much larger than that of the actual delay time jitter (within 2.5ns) in a sense of the multiformity of grain sizes.

Microstructures of Luminescent nc-Si by Excimer Laser Annealing of a-Si:H

We have reported for the first time on visible photoluminescence (PL) in crystallized a-Si:H/a-SiNx:H multilayer structures by CW Ar ion laser annealing treatments. In this paper we present new results on visible PL from crystallized a-Si:H by using KrF excimer pulse laser (wavelength 248 nm) irradiating treatments. The transmission electron microscopy and Raman scattering studies reveal the microstructures of crystallized Si films, which depend on the pulse number and the pulse energy density of KrF laser. When the laser pulse energy density is higher than 520 mJ/cm2, the nanosized Si crystallites (nc-Si) can be formed from a-Si:H layers with a thickness of 100 nm and strong PL with a peak wavelength of 610 nm has been observed at room temperature.