Optical absorption in fused silica during TRIGA reactor pulse irradiation
Spectral transmission characteristics of fused silica before, during, and after exposure to reactor irradiation pulses
De Crescente, M. A.↗
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Results for “PULSED IRRADIATION”
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Formation of laser-induced periodic surface structures on fused silica upon two-color double-pulse irradiation
The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica with multiple irradiation sequences consisting of laser pulse pairs (50 fs single-pulse duration) of two different wavelengths (400 and 800 nm) is studied experimentally. Parallel polarized double-pulse sequences with a variable delay Δt between −10 and +10 ps and between the individual fs-laser pulses were used to investigate the LIPSS periods versus Δt. These two-color experiments reveal the importance of the ultrafast energy deposition to the silica surface by the first laser pulse for LIPSS formation. The second laser pulse subsequently reinforces the previously seeded spatial LIPSS frequencies.
36 MATERIALS SCIENCE↗
Generation of high spatial frequency ripples on silicon under ultrashort laser pulses irradiation
Periodic high spatial frequency ripples structures have been generated in silicon under femtosecond laser pulses irradiation. The period of the ripples is wavelength dependent. It increases from 110 up to 160 nm when the wavelength varies from 700 to 950 nm, respectively. We propose a refined model of the second harmonic generation ripples spacing theory {Lambda}={lambda}/2n{sub {lambda}*} taking into account the modified femtosecond laser excited silicon refractive index n{sup *} related to the Drude model. Good agreement is found between experimental results and the presented revisited model.
36 MATERIALS SCIENCE↗
Formation of laser-induced periodic surface structures on fused silica upon multiple cross-polarized double-femtosecond-laser-pulse irradiation sequences
The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica with multiple irradiation sequences consisting of five Ti:sapphire femtosecond (fs) laser pulse pairs (150 fs, 800 nm) is studied experimentally. A Michelson interferometer is used to generate near-equal-energy double-pulse sequences with a temporal pulse delay from -20 to +20 ps between the cross-polarized individual fs-laser pulses ({approx}0.2 ps resolution). The results of multiple double-pulse irradiation sequences are characterized by means of Scanning Electron and Scanning Force Microscopy. Specifically in the sub-ps delay domain striking differences in the surface morphologies can be observed, indicating the importance of the laser-induced free-electron plasma in the conduction band of the solids for the formation of LIPSS.
36 MATERIALS SCIENCE↗
Enhancement of K{sub {alpha}} emission through efficient hot electron generation in carbon nanotubes on intense laser pulse irradiation
Near complete absorption of the energy of intense ultra-short laser pulses (45 fs, intensity {approx}1.6 Multiplication-Sign 10{sup 16} to 2.5 Multiplication-Sign 10{sup 17} W/cm{sup 2}) is observed in carbon nanotubes deposited on a planar molybdenum substrate. The hollow structure of the nanotube plasma facilitates resonant electric field enhancement during its ionization phase. This resonantly enhanced localized field at a density much larger than the critical density n{sub c} leads to efficient hot electron generation, which results in enhanced K{sub {alpha}} emission of Mo at 17.5 keV. It is observed that for nanotubes, depending on the degree of hollowness, there is an optimum laser intensity for maximum x-ray enhancement compared to a planar uncoated target.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Time response of Cd{sub 0.9}Zn{sub 0.1}Te crystals under transient and pulsed irradiation
A CdZnTe detector based on high-quality Cd{sub 0.9}Zn{sub 0.1}Te crystals was developed and tested as a monitor in high-intensity radiation fields. The current-voltage measurements were performed using thermally evaporated Au contacts deposited on the crystals, which revealed resistivity of 10{sup 10}{Omega}{center_dot}cm. Typical leakage current for the planar devices was {approx}3 nA for a field strength of 1000 V{center_dot}cm{sup -1}. The test results show that the CdZnTe detector has a fast time response, with a rise time of approximately 2 ns, when exposed to transient and pulsed irradiation of X-rays or electron beams. The decay of current curves is observed and discussed according to charge carrier trapping effects and space-charge accumulation mechanisms. It is suggested that the current decreases quickly with strengthening of the electric field, possibly because of charge de-trapping.
36 MATERIALS SCIENCE↗
Nanosecond Pulsed Laser Irradiation of Titanium: Oxide Growth and Effects on Underlying Metal.
Abstract not provided.
Adams, David Price↗
Photothermal transformation of Au–Ag nanocages under pulsed laser irradiation
Pulsed laser irradiation can photothermally transform Au–Ag nanocages into pseudo-spherical, solid nanoparticles. The results may have implications for the future use of Au–Ag nanocages in biomedicine, catalysis, and sensing.
Hood, Zachary D.↗
Determination of Refractive Indices of a Layered Medium under Pulsed Irradiation
Problems related to determination of refractive indices of layered strongly scattering biological media by means of an optical tomography are investigated. Methods of reconstruction of refractive indices of layers, which are based on the smoothness properties of the solution to the initial-boundary problem, are proposed within the framework of the nonstationary radiative-transfer model. The influence of the probe-pulse duration on the accuracy of recovery of the sought-for characteristics of the medium is investigated numerically.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Optical absorption and fluorescence in fused silica during TRIGA pulse irradiation
Spectral transmission measurements on fused silica during and after exposure to pulsed neutron irradiation
Gagosz, R.↗
Magnetic-field generation by pulsed irradiation of aluminium in air
Magnetic-field generation arising under irradiation of an aluminium barrier in the air by a series of laser pulses is studied experimentally. It is found that the magnetic field increases nonlinearly from 10{sup -5} to 10{sup -3} T with increasing laser power density from 10{sup 7} to 10{sup 9} W cm{sup -2}, the degree of nonlinearity being different for single nanosecond pulses, for a series of such pulses with a repetition rate of 100 – 150 μs and for a combination of a millisecond laser pulse and a series of nanosecond laser pulses. The dependences of the magnetic-field induction on the power density of laser radiation in the above-mentioned regimes are established. (interaction of laser radiation with matter)
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Effect of focused nanosecond laser pulse irradiation on microtribological properties of diamond-like films
We have examined the effect of focused nanosecond laser pulses on the formation and tribological properties of microstructures in the form of a matrix of craters produced in a – C : H : Si : O diamond-like films (DLFs), both undoped and doped with tungsten. The studies are performed by scanning probe microscopy (SPM) using SPM probes of standard design with a tip and probes without a tip (tipless-type probes). A special procedure is developed for assessing the wettability (contact angle) of individual sections of the laser-induced microstructure by the local adhesion force. According to estimates, the material inside the crater becomes softer and more hydrophobic as a result of laser irradiation. This is manifested to the greatest extent in tungsten-doped DLFs, where the crater walls are arranged like terraces formed by ‘nanoflakes’, i.e. grains of the substance. Scanning of microstructures with a tipless probe in the regime of lateral force microscopy demonstrates a decrease in friction in the crater area. (interaction of laser radiation with matter. laser plasma)
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Godiva II—An Unmoderated Pulse-Irradiation Reactor
Design features of Godiva II, the improved pulsed reactor successor to Lady Godiva, are discussed together with characteristics of power excursions, and performance is compared with that of the original Godiva. Measurements of the wait time between stepwise reactivity insertion and the occurrence of a burst are presented and compared with theory based on a statistical model of fission chains. Analytical and numerical solutions of the reactor equations are developed to reproduce experimental data and extrapolate to higher energy release. Here, consideration is also given to perturbations arising from room-returned neutrons. Two different modes of operation are discussed and some design problems of Godiva-type pulsed reactors are briefly mentioned. Typical bursts are illustrated with peak powers up to 13,000 Mw and widths at half-maximum down to 35 μsec.
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
Removal of water from a shallow bath under laser pulse irradiation
An experimental investigation was made of water removal from a shallow bath under the action of a CO{sub 2}-laser radiation pulse focused to a spot of size substantially smaller than the bath length. We showed that the specific expenditure of energy is determined by the intensity of laser radiation at the water surface for different values of the focal spot area and pulse duration. The removal dynamics was studied by single-frame photography technique. It was determined that the water is removed layerwise only from the walls of the cavern, which expands in the horizontal direction upon cessation of the radiation pulse. Two-dimensional numerical simulations were made of the water removal, and a mechanism was proposed to explain the experimentally observed removal pattern. (interaction of laser radiation with matter)
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Target optimisation for the yield of X-rays of desired hardness under femtosecond pulse irradiation
Different regimes of electron acceleration from solid foils and low-density targets are investigated using three-dimensional numerical simulations. The size of the plasma corona is shown to be the main parameter characterising the temperature and number of hot electrons, which determine the yield of X-ray radiation and its hardness. Also studied is the generation of X-ray radiation by laseraccelerated electrons, which bombard the converter target located behind the laser target. (extreme laser radiation: physics and fundamental applications)
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Primary radical yields in pulse irradiated alkaline aqueous solution
Primary radical yields of hydrated electrons, H atoms, and OH radicals are determined by measuring hydrated electron formation following a 4 microsecond pulse of X rays. The pH dependence of free radical yields beyond pH 12 is determined by observation of the hydrated electrons.
Fielden, E. M.↗
Efficient multi-keV x-ray source generated by nanosecond laser pulse irradiated multi-layer thin foils target
A new target configuration is proposed to generate efficient multi-keV x-ray source using multiple thin foils as x-ray emitters. The target was constructed with several layers of thin foils, which were placed with a specific, optimized spacing. The thin foils are burned though one by one by a nanosecond-long laser pulse, which produced a very large, hot, underdense plasma. One-dimensional radiation hydrodynamic simulations show that the emission region and the multi-keV x-ray flux generated by multi-layer thin foil target are similar to that of the low-density gas or foam target, which is currently a bright multi-keV x-ray source generated by laser heating. Detailed analysis of a range of foil thicknesses showed that a layer-thickness of 0.1 μm is thin enough to generate an efficient multi-keV x-ray source. Additionally, this type of target can be easily manufactured, compared with the complex techniques for fabrication of low-density foam targets. Our preliminary experimental results also verified that the size of multi-keV x-ray emission region could be enhanced significantly by using a multi-layer Ti thin foil target.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Environmental resistance of oxide tags fabricated on 304L stainless steel via nanosecond pulsed laser irradiation
Nanosecond pulsed laser irradiation was used to fabricate colored, mechanically robust oxide “tags” on 304L stainless steel. Immersion in simulated seawater solution, salt fog exposure, and anodic polarization in a 3.5% NaCl solution were employed to evaluate the environmental resistance of these oxide tags. Single layer oxides outside a narrow thickness range (~ 100–150 nm) are susceptible to dissolution in chloride containing environments. The 304L substrates immediately beneath the oxides corrode severely—attributed to Cr-depletion in the melt zone during laser processing. For the first time, multilayered oxides were fabricated with pulsed laser irradiation in an effort to expand the protective thickness range while also increasing the variety of film colors attainable in this range. Layered films grown using a laser scan rate of 475 mm/s are more resistant to both localized and general corrosion than oxides fabricated at 550 mm/s. Furthermore, in the absence of pre-processing to mitigate Cr-depletion, layered films can enhance environmental stability of the system.
54 ENVIRONMENTAL SCIENCES↗