Wide Range Of Fluences Research Articles

Effect of Laser Pulse Overlap and Scanning Line Overlap on Femtosecond Laser-Structured Ti6Al4V Surfaces.

Surface structuring is a key factor for the tailoring of proper cell attachment and the improvement of the bone-implant interface anchorage. Femtosecond laser machining is especially suited to the structuring of implants due to the possibility of creating surfaces with a wide variety of nano- and microstructures. To achieve a desired surface topography, different laser structuring parameters can be adjusted. The scanning strategy, or rather the laser pulse overlap and scanning line overlap, affect the surface topography in an essential way, which is demonstrated in this study. Ti6Al4V samples were structured using a 300 fs laser source with a wavelength of 1030 nm. Laser pulse overlap and scanning line overlap were varied between 40% and 90% over a wide range of fluences (F from 0.49 to 12.28 J/cm²), respectively. Four different main types of surface structures were obtained depending on the applied laser parameters: femtosecond laser-induced periodic surface structures (FLIPSS), micrometric ripples (MR), micro-craters, and pillared microstructures. It could also be demonstrated that the exceedance of the strong ablation threshold of Ti6Al4V strongly depends on the scanning strategy. The formation of microstructures can be achieved at lower levels of laser pulse overlap compared to the corresponding value of scanning line overlap due to higher heat accumulation in the irradiated area during laser machining.

Treatment of pastirma with pulsed UV light: Modeling of Staphylococcus aureus inactivation and assessment of quality changes.

The efficacy of pulsed UV (PUV) light treatment carried out in a wide range of fluence was investigated on pastirma slices by characterizing Staphylococcus aureus inactivation using mathematical models and by assessing the treatment effects on quality attributes. Pastirma slices inoculated on top surface with S. aureus were subjected to pulsed UV light for 5, 15, 25, 35, and 45 s at 5, 8, and 13 cm from the quartz window. Although the 5 cm/45 s treatment (72.3 J/cm2) yielded a maximum reduction of 2.99 log cfu/cm2 for S. aureus, this treatment changed the color, moisture, and thiobarbituric acid-reactive substances (TBARS) values of pastirma significantly (p < 0.05). The quality of pastirma tended to change above 20 J/cm2, below which the highest log reduction of S. aureus was ∼1.3 log cfu/cm2 obtained after the 8 cm/15 s treatment (18 J/cm2). Kamau's model provided better fit to inactivation data (root mean square error: 0.049-0.116, Af: 1.013-1.046, R2: 0.991-0.999) than Cerf's and Weibull models.

Photoenhanced metastable c-axis electrodynamics in stripe-ordered cuprate La1.885Ba0.115CuO4

Quantum materials are amenable to nonequilibrium manipulation with light, enabling modification and control of macroscopic properties. Light-based augmentation of superconductivity is particularly intriguing. Copper-oxide superconductors exhibit complex interplay between spin order, charge order, and superconductivity, offering the prospect of enhanced coherence by altering the balance between competing orders. We utilize terahertz time-domain spectroscopy to monitor the c-axis Josephson plasma resonance (JPR) in La2-xBaxCuO4 (x = 0.115) as a direct probe of superconductivity dynamics following excitation with near-infrared pulses. Starting from the superconducting state, c-axis polarized excitation with a fluence of 100 μJ/cm2 results in an increase of the far-infrared spectral weight by more than an order of magnitude as evidenced by a blueshift of the JPR, interpreted as resulting from nonthermal collapse of the charge order. The photoinduced signal persists well beyond our measurement window of 300 ps and exhibits signatures of spatial inhomogeneity. The electrodynamic response of this metastable state is consistent with enhanced superconducting fluctuations. Our results reveal that La2-xBaxCuO4 is highly sensitive to nonequilibrium excitation over a wide fluence range, providing an unambiguous example of photoinduced modification of order-parameter competition.

Influence of carbon-ion irradiation on the superconducting critical properties of MgB2 thin films

We investigate the influence of carbon-ion irradiation on the superconducting (SC) critical properties of MgB2 thin films. MgB2 films of two thicknesses, 400 nm (MB400nm) and 800 nm (MB800nm), were irradiated by 350 keV C ions having a wide range of fluence, 1 × 1013–1 × 1015 C atoms cm−2. The mean projected range (R p) of 350 keV C ions in MgB2 is 560 nm, thus the energetic C ions will pass through the MB400nm, whereas the ions will remain into the MB800nm. The SC transition temperature (T c), upper critical field (H c2), c-axis lattice parameter, and corrected residual resistivity (ρ corr) of both the films showed similar trends with the variation of fluence. However, a disparate behavior in the SC phase transition was observed in the MB800nm when the fluence was larger than 1 × 1014 C atoms cm−2 because of the different T cs between the irradiated and non-irradiated parts of the film. Interestingly, the SC critical properties, such as T c, H c2, and critical current density (J c), of the irradiated MgB2 films, as well as the lattice parameter, were almost restored to those in the pristine state after a thermal annealing procedure. These results demonstrate that the atomic lattice distortion induced by C-ion irradiation is the main reason for the change in the SC properties of MgB2 films.

Effect of Epitaxial Stresses on the Time Dynamics of Photoexcited Charge Carriers in InGaAs–Based Superlattices

ABSTRACTWe report on the time-resolved measurements of photocarrier dynamics in InGaAs/InAlAs superlattices with epitaxial stresses in a wide range of optical pump fluences. We demonstrated that the contribution of free carrier absorption and two-photon absorption to the carrier dynamics decreases with an increase of epitaxial stresses. The lowest relaxation times of 1.7 and 8.3 ps, respectively attributed to carrier trapping and carrier recombination, were obtained for the structure with maximum epitaxial stresses.

Comparison of irradiation tolerance of two MAX phases-Ti4AlN3 and Ti2AlN

The microstructures of two MAX phases, Ti2AlN and Ti4AlN3, irradiated at room temperature with 70 keV He ions over a wide fluence range have been studied to reveal the dependence of MAX phase irradiation tolerance on structure. Grazing incident x-ray diffraction (GIXRD) reveals that a new set of diffraction peaks appears after ion irradiation for both MAX phases and the positions of diffraction peaks gradually shift towards lower 2θ values with increasing fluence. Transmission electron microscope characterizations show both MAX phases experience a similar structure transformation at low fluences, forming an intermediate structure. The d-spacings derived from electron diffraction analysis of intermediate structures are basically consistent with that of new peaks in GIXRD. At high fluences a nano-twinned microstructure is found in Ti2AlN, but no such microstructure is observed in Ti4AlN3. Based on the simulation results of electron diffractions and the irradiation responses of other MAX phases, the structure characteristics and formation mechanisms of the intermediate structure are derived and the discrepancy in the phase stability of both MAX phases at high fluences is discussed.

Phononic crystal as a neutron detector

A perfect phononic crystal model composed of concrete and epoxy, and another defect model of Aluminum/Concrete/Epoxy were proposed. The two models were analyzed computationally and theoretically based on the transfer matrix method. The proposed models were capable of detecting and sensing neutrons irradiations over a wide fluence range based on the effects of neutrons fluence on the Young's modulus of the concrete. The neutrons fluence significantly changed the transmission spectra of the phononic crystal models whether the neutrons-induced temperature was considered or not as the phononic band gaps and the local resonant peaks were shifted. Also, neutrons irradiations made a strong dispersion in the conventional parameters of the proposed phononic crystal models. The results presented in this work might pave the way for designing an effective detector that works over a wide range of neutron fluence.

Laser threshold and cell damage mechanism for intravascular photoacoustic imaging.

Intravascular photoacoustic (IVPA) imaging is being developed to image atherosclerotic plaques, a leading cause of morbidity and mortality in the United States. However, the safety of this imaging modality, which requires repeated irradiation with short laser pulses, has not yet been investigated. This study has two objectives. First, determine in vitro the limit of cumulative fluence that can be applied to cells before death at IVPA relevant wavelengths. Second, evaluate if high single pulse fluences are a potential cause of cell death during IVPA imaging. Experiments were conducted using endothelial cells, macrophages, and smooth muscle cells. The cumulative fluence experiments were conducted at 1064 and 1197 nm, using a high pulse repetition frequency laser. Cells were irradiated with a wide range of cumulative fluences and evaluated for cell death. The thresholds for death were compared to the maximum expected clinical cumulative fluence. To evaluate the effect of single pulse fluences, cells were irradiated at 1064, 1210, and 1720 nm. Light was delivered at a range of pulse energies to emulate the fluences that cells would be exposed to during clinical IVPA imaging. At 1064 nm, all three cell types remained viable at cumulative fluences above the maximum expected clinical cumulative fluence, which is calculated based on common IVPA imaging protocols. At 1197 nm, cells were viable near or just below the maximum expected clinical cumulative fluence, with some cell type to cell type variation. All three cell types remained viable after irradiation with high single pulse fluences at all three wavelengths. The cumulative fluence experiments indicate that safety considerations are likely to put constraints on the amount of irradiation that can be used in IVPA imaging protocols. However, this study also indicates that it will be possible to use IVPA imaging safely, since cumulative fluences could be reduced by as much as two orders of magnitude below the maximum expected clinical cumulative fluence by varying the imaging protocol, albeit at the expense of image quality. The single pulse fluence experiments indicate that cell death from single pulse fluence is not likely during IVPA imaging. Thus, future studies should focus on heat accumulation as the likely mechanism of tissue damage. Lasers Surg. Med. 51:466-474, 2019. © 2018 Wiley Periodicals, Inc.

Effects of He ion irradiation on the microstructures and mechanical properties of t' phase yttria-stabilized zirconia ceramics

Abstract The dense ZrO2-8 wt.% Y2O3 ceramics with tetragonal (t') phase were prepared by spark plasma sintering (SPS). The micro-structure modification in poly-crystalline t' phase YSZ ceramics irradiated with 60 KeV He ions over a wide fluence range were studied. It is found that, the t' → t + c phase transformation was detected for the samples irradiated at the fluence above 2 × 1017 cm−2. In addition, a three-steep model for damage stages has been proposed and discussed for interpreting the evolution of mechanical properties of t'-YSZ ceramics after irradiated, mainly revealed by the analysis from HRTEM results. Firstly, as the He+ fluences range from 0.5 × 1017 cm−2 to 1 × 1017 cm−2, the hardening effects were confirmed in t'-YSZ owing to the irradiation induced defects serve as obstacles to resist slipping of dislocations. As the fluence was increased to 2 × 1017 cm−2, the degradation of mechanical properties was evidenced, which could be ascribed to the deterioration effect of aggregated He bubbles inside t' YSZ grains. While the fluence increased to 10 × 1017 cm−2, a seriously damaged region was approximately located at 250 nm in depth, at which a great number of He bubbles with different shape and dislocation loops were evidenced, leading to a further reduction of hardness and elastic modulus. No micro-cracks emerge even for He+ fluences as high as 10 × 1017 cm−2, indicating high irradiation stability and resistance to micro-crack propagation in t'-YSZ.

Effect of ballistic damage in UO2 samples under ion beam irradiations studied by in situ Raman spectroscopy

Abstract The damage induced in uranium dioxide (UO2) during ion irradiation at low energy was studied by micro-Raman spectroscopy. Polycrystalline UO2 samples were irradiated by 0.9-MeV I, 2-MeV Au at 25 °C and by 4-MeV Kr ions at −160 °C in a wide range of fluences. In situ Raman measurements show similar spectra evolution no matter the ion beam used. The T2g band centred at 445 cm−1 related to the fluorine structure reveals a broadening with the irradiation damage increase. In addition, several bands ranging from 500 to 700 cm−1, which are attributed to sub- or sur-stoichiometric structural defects, are observed at the early stages of irradiation. Their intensities grow with the irradiation fluence to similar asymptotic relative values for all the irradiation conditions. The obtained Raman kinetics are compared with data from the literature on the microstructure evolution observed by Transmission Electronic Microscopy (TEM) and on the fraction of displaced atoms determined by Rutherford Backscattering Spectroscopy in channelling mode (RBS-C).

Toward a comprehensive UV laser ablation modeling of multicomponent materials—A non-equilibrium investigation on titanium carbide

Titanium carbide (TiC) coatings of great quality can be produced using nanosecond pulsed laser deposition (PLD). Because the deposition rate and the transfer of the target stoichiometry depend strongly on the laser-target/laser-plasma interaction as well as the composition of the laser induced plume, investigating the ruling fundamental mechanisms behind the material ablation and the plasma evolution in the background environment under PLD conditions is essential. This work, which extends previous investigations dedicated to the study of nanosecond laser ablation of pure target materials, is a first step toward a comprehensive non-equilibrium model of multicomponent ones. A laser-material interaction model coupled to a laser-plasma interaction one is presented. A UV 20 ns KrF (248 nm) laser pulse is considered. Ablation depths, plasma ignition thresholds, and shielding rates have been calculated for a wide range of laser beam fluences. A comparison of TiC behavior with pure titanium material under the same conditions is made. Plasma characteristics such as temperature and composition have been investigated. An overall correlation between the various results is presented.

Nanosecond laser-metal ablation at different ambient conditions

Ablation of metals under different ambient conditions and laser fluences, was investigated through series of experiments. A 1064nm, 6ns Nd:YAG laser was used to ablate 1mm thick metal targets with laser energy ranging from 2mJ to 300mJ. The experiments were designed to study the effect of material properties, laser fluence, ambient gas, and ambient pressure on laser-metal ablation. The first experiment was conducted under vacuum to study the effect of laser fluence and material properties on metal ablation, using a wide range of laser fluences (2J/cm2 up to 300J/cm2) and two different targets, Al and W. The second experiment was conducted at atmospheric pressure using two different ambient gases air and argon, to understand the effect of ambient gas on laser-metal ablation process. The third experiment was conducted at two different pressures (10Torr and 760Torr) using the same ambient gas to investigate the effect of ambient pressure on laser-metal ablation. To compare the different ablation processes, the amount of mass ablated, ablation depth, crater profile and melt formation were measured using White Light Profilometer (WLP). The experimental results show that at low laser fluence: the ablated mass, ablation depth, and height of molten layer follow a logarithmic function of the incident laser fluence. While, at high laser fluence they follow a linear function. This dependence on laser fluence was found to be independent on ambient conditions and irradiated material. The effect of ambient pressure was more pronounced than the effect of ambient gas type. Plasma shielding effect was found to be very pronounced in the presence of ambient gas and led to significant reduction in the total mass ablation.

Optical properties of silicon-vacancy color centers in diamond created by ion implantation and post-annealing

Silicon-vacancy (SiV) color centers have been created in diamond by ion implantation and post annealing at LABEC (Florence). A wide range of implantation depths (0–2.4 μm) and fluences (108–1015 cm−2), along with a variety of substrates (single and poly-crystals) have been explored. The photoluminescence properties of the SiV centers have been studied at room temperature, including their single-photon emission characteristics. Single-photon emitters have been obtained at the lower-end of the implantation fluences range. They exhibit a short excited-state lifetime (~1 ns), a strong zero-phonon transition with a narrow linewidth (~1.6 nm) and a very small inhomogeneous broadening (0.015 nm), features that qualify them for application in quantum optical technologies. The activation yield of SiV centers has been assessed under different experimental conditions. It has been found to be independent of the implantation energy and in the range of 3% after thermal annealing.

The center for production of single-photon emitters at the electrostatic-deflector line of the Tandem accelerator of LABEC (Florence)

Abstract The line for the pulsed beam of the 3 MeV Tandetron accelerator at LABEC (Florence) has been upgraded for ion implantation experiments aiming at the fabrication of single-photon emitters in a solid-state matrix. A system based on Al attenuators has been calibrated in order to extend the energy range of the implanted ions from MeV down to the tens of keV. A new motorized XY stage has been installed in the implantation chamber for achieving ultra-fine control on the position of each implanted ion, allowing to reach the scale imposed by lateral straggling. A set-up for the activation of the implanted ions has been developed, based on an annealing furnace operating under controlled high-vacuum conditions. The first experiments have been performed with silicon ions implanted in diamond and the luminescent signal of the silicon-vacancy (SiV) center, peaked at 738 nm, has been observed for a wide range of implantation fluences (108 ÷ 1015 cm−2) and implantation depths (from a few nm to 2.4 µm). Studies on the efficiency of the annealing process have been performed and the activation yield has been measured to range from 1% to 3%. The implantation and annealing facility has thus been tuned for the production of SiV centers in diamond, but is in principle suitable for other ion species and solid-state matrices.

Revealing ionization-induced dynamic recovery in ion-irradiated SrTiO3

The lack of fundamental understanding on the coupled effects of energy deposition to electrons and atomic nuclei on defect processes and irradiation response poses a significant roadblock for the design and control of material properties. In this work, SrTiO3 has been irradiated with various ion species over a wide range of ion fluences at room temperature with a goal to deposit different amounts of energy to target electrons and atomic nuclei by varying the ratio of electronic to nuclear energy loss. The results unambiguously show a dramatic difference in behavior of SrTiO3 irradiated with light ions (Ne, O) compared to heavy ions (Ar). While the damage accumulation and amorphization under Ar ion irradiation are consistent with previous observations and existing models, the damage accumulation under Ne irradiation reveals a quasi-saturation state at a fractional disorder of 0.54 at the damage peak for an ion fluence corresponding to a dose of 0.5 dpa; this is followed by further increases in disorder with increasing ion fluence. In the case of O ion irradiation, the damage accumulation at the damage peak closely follows that for Ne ion irradiation up to a fluence corresponding to a dose of 0.5 dpa, where a quasi-saturation of fractional disorder level occurs at about 0.48; however, in this case, the disorder at the damage peak decreases slightly with further increases in fluence. This behavior is associated with changes in kinetics due to irradiation-enhanced diffusional processes that are dependent on electronic energy loss and the ratio of electronic to nuclear energy dissipation. These findings are critical for advancing the fundamental understanding of ion-solid interactions and for a large number of applications in oxide electronics where SrTiO3 is a foundational material.

Tungsten borides layers deposited by a nanosecond laser pulse

Tungsten borides belong to the group of potentially superhard materials which hardness could be compared to cubic boron nitride and diamond. However, difficulty in fabrication of single phase material using conventional methods is the main drawback of this group of ceramics. In order to overcome this problem material can be deposited as a thin layer e.g. in the pulsed laser deposition process. In this paper, the effect of laser wavelength and energy density of nanosecond Nd:YAG laser on the WBx-type layers were analyzed using wavelengths 355 and 1064nm with the energy density of laser beam from 1.7 to 5J/cm2 and from 1.7 to 9.3J/cm2, respectively. The WB2.5 and WB4.5 targets synthesized in Spark Plasma Sintering process were used and the layers were deposited onto Si (100) substrate heated to a temperature of 570°C. Layers' microstructure were analyzed using X-ray Diffraction and scanning electron microscope equipped with energy dispersive X-ray spectrometer. Change of laser wavelength and energy density resulted in variations of the chemical composition and morphology of deposited layers. Finally, W2B-βWB, αWB-WB-WB3 and WB3, and boron layers were deposited wherein WB3 structure is formed in a wide range of laser fluences and at both investigated wavelength. Next, WB3 layers were investigated in the indentation test at a load of 5–30mN and its hardness was up to 50±10GPa.

Raman spectroscopy study of damage induced in cerium dioxide by swift heavy ion irradiations

The damage induced in cerium dioxide by swift heavy ion irradiation was studied by micro-Raman spectroscopy. For this purpose, polycrystalline sintered pellets were irradiated by 100-MeV Kr, 200-MeV Xe, 10-MeV, and 36-MeV W ions in a wide range of fluence and stopping power (up to ∼28 MeV μm−1). No amorphization of ceria was found whatsoever, as shown by the presence of the peak of Raman-active T2g mode (centered at 467 cm−1) of the cubic fluorite structure for all irradiation conditions. However, a clear decrease of the T2g mode peak intensity was observed as a function of ion fluence to an asymptotic relative value of about 45%. Similar decays were also observed for satellite peaks and second-order peaks. Track radii deduced from the decay kinetics for the 36-MeV W ion data are in good agreement with previous determinations by X-ray diffraction and reproduced by the inelastic thermal spike model for low ion velocities. However, interaction between the nuclear and electronic stopping powers is needed to describe the decay kinetics of 10-MeV W ion data by the thermal spike process. Moreover, the asymmetrical broadening of the main T2g peak after irradiation was analyzed with different theoretical models.

Radiation hardness of Silicon Photomultipliers for CBM@FAIR, NA61@CERN and BM@N experiments

Results of radiation hardness study of Silicon Photomultipliers (SiPMs) to be used at forward hadron calorimeters, including designed Projectile Spectator Detector (PSD) of CBM, PSD of NA61 beyond 2020 upgrade and Zero Degree Calorimeter (ZDC) at BM@N are presented. High intensity beams at future heavy-ion accelerator facilities up to 106∕107 interactions/second will lead to high neutron fluence around calorimeters up to 3×1012 neq/cm2 accumulated during a year of the experiment operation. SiPMs produced by Ketek, Zecotek, Hamamatsu and Sensl manufacturers were irradiated at cyclotron of NPI Rez in a wide range of neutron fluences from 4×1010 up to 6×1012 n/cm2. Change of SiPM’s main parameters after irradiation including dark current, breakdown voltage, noise and signal response to LED was studied in the lab. Furthermore, several packs of irradiated SiPMs were installed at the currently operating NA61 PSD to study the cumulative radiation effect on the calorimeter performance. Beam scan with 20–80 GeV/c protons was performed to determine the dependency of detector energy resolution on beam energy before and after irradiation.

Laser-assisted fabrication of gold nanoparticle-composed structures embedded in borosilicate glass.

We present results on laser-assisted formation of two- and three-dimensional structures comprised of gold nanoparticles in glass. The sample material was gold-ion-doped borosilicate glass prepared by conventional melt quenching. The nanoparticle growth technique consisted of two steps – laser-induced defect formation and annealing. The first step was realized by irradiating the glass by nanosecond and femtosecond laser pulses over a wide range of fluences and number of applied pulses. The irradiation by nanosecond laser pulses (emitted by a Nd:YAG laser system) induced defect formation, expressed by brown coloration of the glass sample, only at a wavelength of 266 nm. At 355, 532 and 1064 nm, no coloration of the sample was observed. The femtosecond laser irradiation at 800 nm also induced defects, again observed as brown coloration. The absorbance spectra indicated that this coloration was related to the formation of oxygen deficiency defects. After annealing, the color of the irradiated areas changed to pink, with a corresponding well-defined peak in the absorbance spectrum. We relate this effect to the formation of gold nanoparticles with optical properties defined by plasmon excitation. Their presence was confirmed by high-resolution TEM analysis. No nanoparticle formation was observed in the samples irradiated by nanosecond pulses at 355, 532 and 1064 nm. The optical properties of the irradiated areas were found to depend on the laser processing parameters; these properties were studied based on Mie theory, which was also used to correlate the experimental optical spectra and the characteristics of the nanoparticles formed. We also discuss the influence of the processing conditions on the characteristics of the particles formed and the mechanism of their formation and demonstrate the fabrication of structures composed of nanoparticles inside the glass sample. This technique can be used for the preparation of 3D nanoparticle systems embedded in transparent materials with potential applications in the design of new optical components, such as metamaterials and in plasmonics.

Irradiation-induced defect formation and damage accumulation in single crystal CeO2

The accumulation of irradiation-induced disorder in single crystal CeO2 has been investigated over a wide range of ion fluences. Room temperature irradiations of epitaxial CeO2 thin films using 2 MeV Au2+ ions were carried out up to a total fluence of 1.3×1016 cm−2 Post-irradiation disorder was characterized using ion channeling Rutherford backscattering spectrometry (RBS/C) and confocal Raman spectroscopy. The Raman measurements were interpreted by means of a phonon confinement model, which employed rigid ion calculations to determine the phonon correlation length in the irradiated material. Comparison between the dose dependent changes in correlation length of the Raman measurements and the Ce disorder fraction from RBS/C provides complementary quantitative details on the rate of point and extended defect formation on the Ce and O sub-lattices over a broad range of ion fluences. Raman measurements, which are significantly more sensitive than RBS/C at low doses, reveal that the nucleation rate of defects is highest below 0.1 displacements per atom (dpa). Comparison between Raman and RBS/C measurements suggests that between 0.1 and 10 dpa the damage evolution is characterized by modest growth of point defects and/or small clusters, while above 10 dpa the preexisting defects rapidly grow into extended clusters and/or loops.