Average Fluence Research Articles

Characterization on deuterium retention in tungsten target using spatially resolved laser induced desorption-quadrupole mass spectroscopy

It is still challenging to achieve the quantitative analysis with a spatially resolved measurement for a non-uniform fuel retention in Plasma Facing Materials (PFMs). In this work, a long-pulse (τ p ≈ 750 μs) Laser Induced Desorption-Quadrupole Mass Spectroscopy (LID-QMS) has been developed as a diagnostic approach for characterizing inhomogeneous deuterium (D) retention in tungsten (W) target exposed to D plasma for ∼1 h with the total ion flux of 4.0 × 1021 D/(m2 s) at the substrate temperature of 400 K. The behavior of desorption of trapped D during LID was analyzed. 2D-distribution features of D retention in the exposed and shadowed areas of the W-target were investigated with a lateral resolution of about 650 μm and depth resolution of approximately 175 μm. The results show that the D retention is almost uniform along lateral dimension in the D plasma exposure area with an average fluence of (2.51 ± 0.40) × 1020 D m−2, while the value in the shadow area is only (0.25 ± 0.04) × 1020 D m−2 which is one order of magnitude smaller than that in the exposure region. In the depth dimension, about 86.5% of the retained D is desorbed by the first laser pulse, which indicates that the D-retention is mainly distributed in the region less than 6.6 μm based on the diffusion length. The micro-structures of W target exposed to D plasma after the long-pulse laser irradiation present swelling, blistering as well as bubble-bursting, which might be attributed to the thermodynamic interaction due to the rapid release of D particles from bulk to surface of W target during LID.

Laser ablation of lanthanum phosphate for pulsed laser deposition

AbstractA theoretical model has been used to simulate pulsed laser ablation of Lanthanum Phosphate (LaPO4) by nanosecond Nd:YAG laser irradiation. Material ablation rate per laser pulse was experimentally measured as a function of average incident laser fluence up to 12J/cm2. Calculations were performed by solving the heat conduction equation by an explicit finite‐difference technique to generate time evolution of temperature distribution, melt depth and ablation rate from the target during and after irradiation with a nanosecond laser pulse. Good agreement between our experimental and calculated ablation rates validates our theoretical model. The calculated maximum surface temperature of the LaPO4 target indicated that for laser fluence levels, up to 20J/cm2 material ejection from LaPO4 target is expected to occur via normal boiling and evaporation successfully avoiding explosive boiling. Our calculations confirm that operating with laser fluence at near ablation threshold levels for LaPO4 also restricts dissociation of the LaPO4 target to oxides with loss of gaseous products. Therefore, our study of pulsed laser ablation of LaPO4 target helps in making judicious selection of laser parameters for Pulsed Laser Deposition (PLD) of LaPO4 coatings and films of desired stoichiometric purity and homogeneity, while successfully ensuring phase stability of the target.

Absence of Bursts between 4 and 8 GHz from FRB 20200120E Located in an M81 Globular Cluster

Abstract We report the non-detection of dispersed bursts between 4 and 8 GHz from 2.5 hr of observations of FRB 20200120E at 6 GHz using the Robert C. Byrd Green Bank Telescope. Our fluence limits are several times lower than the average burst fluences reported at 600 and 1400 MHz. We conclude that these non-detections are either due to high-frequency bursts being weaker and/or scintillation-induced modulated. It is also likely that our observations were non-concurrent with any activity window of FRB 20200120E.

UV light-emitting diode (UV-LED) at 265 nm as a potential light source for disinfecting human platelet concentrates.

The risk of sepsis through bacterial transmission is one of the most serious problems in platelet transfusion. In processing platelet concentrates (PCs), several methods have been put into practice to minimize the risk of bacterial transmission, such as stringent monitoring by cultivation assays and inactivation treatment by photoirradiation with or without chemical agents. As another potential option, we applied a light-emitting diode (LED) with a peak emission wavelength of 265 nm, which has been shown to be effective for water, to disinfect PCs. In a bench-scale UV-LED exposure setup, a 10-min irradiation, corresponding to an average fluence of 9.2 mJ/cm2, resulted in >2.0 log, 1.0 log, and 0.6 log inactivation (mean, n = 6) of Escherichia coli, Staphylococcus aureus, and Bacillus cereus, respectively, in non-diluted plasma PCs. After a 30-min exposure, platelet counts decreased slightly (18 ± 7%: mean ± SD, n = 7); however, platelet surface expressions of CD42b, CD61, CD62P, and PAC-1 binding did not change significantly (P>0.005), and agonist-induced aggregation and adhesion/aggregation under flow conditions were well maintained. Our findings indicated that the 265 nm UV-LED has high potential as a novel disinfection method to ensure the microbial safety of platelet transfusion.

Degradation of micropolluants in flow-through VUV/UV/H2O2 reactors: Effects of H2O2 dosage and reactor internal diameter

The degradation of atrazine (ATZ), sulfamethoxazole (SMX) and metoprolol (MET) in flow-through VUV/UV/H2O2 reactors was investigated with a focus on the effects of H2O2 dosage and reactor internal diameter (ID). Results showed that the micropollutants were degraded efficiently in the flow-through VUV/UV/H2O2 reactors following the pseudo first-order kinetics (R2 > 0.92). However, the steady-state assumption (SSA) kinetic model being vital in batch reactors was found invalid in flow-through reactors where fluid mixing was less sufficient. With the increase of H2O2 dosage, the ATZ removal efficiency remained almost constant while the SMX and MET removal was enhanced to different extents, which could be explained by the different reactivities of the pollutants towards HO•. A larger reactor ID resulted in lower degradation rate constants for all the three pollutants on account of the lower average fluence rate, but the change in energy efficiency was much more complicated. In reality, the electrical energy per order (EEO) of the investigated VUV/UV/H2O2 treatments ranged between 0.14–0.20, 0.07–0.14 and 0.09–0.26 kWh/m3/order for ATZ, SMX and MET, respectively, with the lowest EEO for each pollutant obtained under varied H2O2 dosages and reactor IDs. This study has demonstrated the efficiency of VUV/UV/H2O2 process for micropollutant removal and the inadequacy of the SSA model in flow-through reactors, and elaborated the influential mechanisms of H2O2 dosage and reactor ID on the reactor performances.

Corrections for photons attenuation and scattering for the extrapolation chamber for measurement of air-kerma strength of 125I brachytherapy source

A type of extrapolation chamber was designed in China Institute of Atomic Energy, CIAE. The chamber was used for the measurement of the air-kerma strength of the medical radiation 125I source on primary standard level. In order to obtain the air-krema strength with a low uncertainty, some correction factors such as photon attenuation and scattering are needed to calculate. Correction factors for different types of 125I seeds were estimated with increasing chamber depth. Based on the relation between ionization current and average photon fluence, attenuation correction factors were calculated with the analytical solution. Additionally, the scattering correction factors were estimated by a suitable method of Monte Carlo simulation. Photon attenuation includes four components. katt-volume, katt-foil, katt-sf, and katt-Al. The differences of correction factors are concerned, mainly due to the variation of chamer depths and 125I seed types. katt-volume increases from 1.001 to 1.005. katt-foil varies between 1.0012 and 1.0014. katt-sf changes from 1.015 to 1.018. katt-Al varies between 1.038 and 1.048, which largely depend on the photon spectrum from the source. Meanwhile, the geometric dimension of the ionization chamber has a great influence on the scattering correction factors. The ksca values vary from 0.9960 to 0.9964 with different chamber depths, which only has 0.04% fluctuation.

Femtosecond laser-induced nanostructures on Fe-30Mn surfaces for biomedical applications

FeMn alloy is a promising biodegradable metal due to its high strength and biocompatibility, but the inadequate degradation rate and poor surface performance impede its further development. To overcome the drawbacks, femtosecond laser surface modification was used to establish nano-ripple structure on the Fe-30Mn alloy surface in this work. After laser texturing, typical nano-ripple structures were established on the alloy surfaces. With the increase of laser average line fluence from 10 to 30 J cm−2, the nano-ripple period decreased and vertical sinuous grooves were formed on the surface, resulting in a high roughness value and a hydrophobic surface. Compared with the polished sample, the nano-ripple structure surface exhibited significant improvement of the actual biodegradation rate. Further, in vitro cell counting kit-8 test showed that the laser surface modification had few effects on the cytocompatibility of Fe-30%Mn alloy. The results indicate its great potential for physical surface modification of biodegradable metals.

Fabrication of a 3D Multi-Depth Reservoir Micromodel in Borosilicate Glass Using Femtosecond Laser Material Processing.

Micromodels are ideal candidates for microfluidic transport investigations, and they have been used for many applications, including oil recovery and carbon dioxide storage. Conventional fabrication methods (e.g., photolithography and chemical etching) are beset with many issues, such as multiple wet processing steps and isotropic etching profiles, making them unsuitable to fabricate complex, multi-depth features. Here, we report a simpler approach, femtosecond laser material processing (FLMP), to fabricate a 3D reservoir micromodel featuring 4 different depths—35, 70, 140, and 280 µm, over a large surface area (20 mm × 15 mm) in a borosilicate glass substrate. The dependence of etch depth on major processing parameters of FLMP, i.e., average laser fluence (), and computer numerically controlled (CNC) processing speed (), was studied. A linear etch depth dependence on was determined while a three-phase exponential decay dependence was obtained for . The accuracy of the method was investigated by using the etch depth dependence on relation as a model to predict input parameters required to machine the micromodel. This study shows the capability and robustness of FLMP to machine 3D multi-depth features that will be essential for the development, control, and fabrication of complex microfluidic geometries.

Characterization of the Ce,Pr:LuAG phosphor for Co-doped aerosol phosphor thermometry

The Ce,Pr:LuAG phosphor is investigated for use in co-doped aerosol phosphor thermometry (APT). The phosphor was characterized by measuring the emission intensity for each ion as a function of excitation laser fluence and temperature. A simplified three-level model was used to interpret and fit the data. The phosphor was then used for co-doped APT temperature-imaging experiments performed in a heated air jet up to a maximum temperature of 694 K. The three-level model fit was used to analyze sources of bias in the imaging measurements. Both ions’ emission intensities show a nonlinear dependence on excitation fluence that can potentially be explained by temperature-dependent ground- and excited-state absorption processes included in the three-level model. Single-shot temperature precision from the temperature-imaging experiments was measured to be 22, 23, and 32 K for mean temperatures of 497, 603, and 694 K, respectively, at a spatial resolution of ~1.12 lp/mm and average fluence of 33 mJ/cm2. The results extend the measurement range for co-doped APT to at least 700 K. The findings also provide a simple model for phosphor signal non-linearity with excitation fluence for low activator ion concentrations, and provide a method for estimating temperature bias from several sources including laser fluence.

A tri-hybrid method to estimate the patient-generated scattered photon fluence components to the EPID image plane

In vivo dosimetry methods can verify the prescription dose is delivered to the patient during treatment. Unfortunately, in exit dosimetry, the megavoltage image is contaminated with patient-generated scattered photons. However, estimation and removal of the effect of this fluence improves accuracy of in vivo dosimetry methods. This work develops a ‘tri-hybrid’ algorithm combining analytical, Monte Carlo (MC) and pencil-beam scatter kernel methods to provide accurate estimates of the total patient-generated scattered photon fluence entering the MV imager.For the multiply-scattered photon fluence, a modified MC simulation method was applied, using only a few histories. From each second- and higher-order interaction site in the simulation, energy fluence entering all pixels of the imager was calculated using analytical methods. For photon fluence generated by electron interactions in the patient (i.e. bremsstrahlung and positron annihilation), a convolution/superposition approach was employed using pencil-beam scatter fluence kernels as a function of patient thickness and air gap distance, superposed on the incident fluence distribution.The total patient-scattered photon fluence entering the imager was compared with a corresponding full MC simulation (EGSnrc) for several test cases. These included three geometric phantoms (water, half-water/half-lung, computed tomography thorax) using monoenergetic (1.5, 5.5 and 12.5 MeV) and polyenergetic (6 and 18 MV) photon beams, 10 × 10 cm2 field, source-to-surface distance 100 cm, source-to-imager distance 150 cm and 40 × 40 cm2 imager.The proposed tri-hybrid method is demonstrated to agree well with full MC simulation, with the average fluence differences and standard deviations found to be within 0.5% and 1%, respectively, for test cases examined here. The method, as implemented here with a single CPU (non-parallelized), takes ∼80 s, which is considerably shorter compared to full MC simulation (∼30 h). This is a promising method for fast yet accurate calculation of patient-scattered fluence at the imaging plane for in vivo dosimetry applications.

A Prospective, Split‐Face, Randomized Study Comparing a 755‐nm Picosecond Laser With and Without Diffractive Lens Array in the Treatment of Melasma in Asians

Treatment of melasma with lasers remains a challenge due to its limited clinical efficacy in addition to high rates of recurrence and side effects. Recently, picosecond lasers have shown favorable results in treatment of benign pigmented lesions. To compare the efficacy and safety of using a 755-nm picosecond laser for the treatment of melasma in a split-face manner, having one side treated with a fractionated beam (diffractive lens array [DLA] coupling) and with a full-beam (flat optics) on the other side. Eighteen subjects presenting with mixed-type melasma were enrolled. Each patient was randomly treated with a 755-nm picosecond laser coupled with DLA on one side of the face and without DLA (flat optics) on the other side. The laser was delivered through an 8-mm spot size with an average fluence of 0.4 J/cm2 at 2.5 Hz for a total of two passes without pulse overlapping. All subjects received five monthly treatments. Subjective (clinical evaluation) and objective (color readings) assessments on the degree of pigment clearance and adverse effects were obtained at 1-, 3-, and 6-month after the final treatment. At 6 months after the last treatment, physician-rating scores were 1.50 ± 0.76 and 1.50 ± 0.65 of the DLA and flat-optics sides, respectively. Pigment clearance significantly improved from 1 to 6 months after the treatment on each side (P = 0.019 on DLA and P = 0.023 on flat-optics sides). No statistically significant differences in physician-rating scores between the two treatment techniques were observed at all follow-up visits. Objective assessments of melasma clearance corresponded to the clinical evaluation. However, the full-beam (flat optics) provided lower incidence of pos-tinflammatory hyperpigmentation than the fractioned one. A 755-nm picosecond laser is safe and effective for the treatment of melasma in dark-skinned individuals. The use of DLA does not provide additional benefit over the flat optics in clearing pigmentation. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Fissure caries inhibition with a CO2 9.3-μm short-pulsed laser-a randomized, single-blind, split-mouth controlled, 1-year clinical trial.

The objective of this randomized, single-blind, split-mouth controlled, clinical trial was to evaluate whether the use of a short-pulsed 9.3-μm CO2 laser increases the caries resistance of occlusal pit and fissures in addition to fluoride therapy over 12months. A total of 60 participants, average age 13.1years, were enrolled. At baseline, second molars were randomized into test and control, and assessed by ICDAS, SOPROLIFE, and DIAGNOdent. An independent investigator irradiated test molars with a CO2 laser (wavelength 9.3μm, pulse duration 4μs, pulse repetition rate 43Hz, beam diameter 250μm, average fluence 3.9J/cm2, 20 laser pulses per spot). Test molars received laser and fluoride treatment, control teeth fluoride alone. Fluoride varnish was applied at baseline and at 6months. After 6 and 12months, teeth were again assessed. A total of 57 participants completed the 6-month and 51 the 12-month recall. Laser-treated surfaces showed very slight ICDAS improvements over time with ICDAS change - 1 in 11% and 8%, no changes (ICDAS change 0) in 68% and 67%, and slightly worsened (ICDAS change 1) in 19% and 24% at 6- and 12-month recalls, respectively, and worsened by two scores in 2% at both recall time points. Control teeth showed significantly higher ICDAS increases, with 47% and 25% showing ICDAS change 0, ICDAS change 1 in 49% and 55%, and ICDAS change 2 in 4% and 20% at 6- and 12-month recalls, respectively. Differences in ICDAS changes between the groups were statistically significant (P = 0.0002 and P < 0.0001; Wilcoxon's signed-rank test, exact). A total of 22% of the participants developed ICDAS 3 scores on the control teeth. Microsecond short-pulsed 9.3-μm CO2 laser irradiation markedly inhibits caries progression in pits and fissures in comparison with fluoride varnish alone. The 9.3-μm CO2 laser irradiation of pits and fissures enhances caries resistance. ClinicalTrials.gov identifier: NCT02357979.

Treatment of Laser-Responsive Dermal Pigmentary Conditions in Type III-IV Asian Skin With a 755-nm Picosecond Pulse Duration Laser: A Retrospective Review of Its Efficacy and Safety.

BACKGROUNDPicosecond lasers have become very popular in the treatment of hyperpigmentation.OBJECTIVEEvaluating the efficacy and safety of picosecond 755-nm laser in treatment of nevi of Ota (NO) and Hori's nevi (HN) in Asians with Fitzpatrick skin Types III/IV.METHODSA retrospective review of patient records at the National Skin Center, Singapore, from 2015 to 2017. Three independent blinded dermatologists assessed pre-and-post treatment photographs using the physician's global assessment (PGA) score (0-clear, 1-almost clear, 2-mild, 3-moderate, and 4-severe).RESULTSThere were 18 cases of NO and 11 cases of HN. Mean treatment sessions were 2.22 (NO; range 1–6) and 3.82 (HN; range 1–6). In the NO group, mean pre-and-post treatment PGA scores were 3.1 and 1.3, respectively (1.8 point change, p-value 0.0002), and average fluence used was 2.02 J/cm2 (range: 1.02–2.38). In the HN group, mean pre-and-post treatment PGA scores were 2.6 and 1.1, respectively (1.5 point change, p-value 0.004), and average fluence was 2.08 J/cm2 (range: 1.98–3.40). Eleven patients (37.9%) experienced postlaser erythema, and 1 (3.4%) patient developed transient postlaser hypopigmentation. No permanent hyper/hypopigmentation was seen.CONCLUSIONThe picosecond 755-nm laser is effective in the treatment of dermal pigmentary conditions in Asians with Fitzpatrick skin Types III/IV, with minimal risk of postlaser complications, and compared with the center's past experience with the Q-switched nanosecond 1064-nm laser, results in faster and more effective pigment clearance.

Plated metal adhesion to picosecond laser-ablated silicon solar cells: Influence of surface chemistry and wettability

This study investigated the influence of UV picosecond laser fluence, used to ablate the SiNx antireflection coating for Ni/Cu/Ag plated p-type Si solar cells, on busbar and finger adhesion and cell electrical performance. Surface chemistry was characterised post-ablation and post-pre-treatment in 7:1 buffered oxide etch (BOE) using a combination of X-ray photoelectron spectroscopy and contact angle measurements. Although growth of laser-induced Si oxides increases with increasing laser fluence, these oxides are effectively removed in the BOE pre-treatment and therefore do not impact plated metal adhesion with busbar pull forces of 1.9 ± 0.7 N/mm being achieved when a laser fluence of 0.63 J/cm2 was used to ablate the busbar openings. It is also revealed that the use of high laser fluence leads to a more hydrophobic surface due to reduced residual SiNx, however the complete wetting of the ablated Si surface can be ensured by the use of surfactants in Ni plating electrolytes. Residual SiNx impacts Ni silicidation and reduces the busbar pull force to values of only 0.8 ± 0.5 N/mm when average laser fluences ≤0.45 J/cm2 are used. Finger dislodgement forces are interestingly shown not to be affected by laser fluence and presence of residual SiNx, providing an opportunity to optimise the laser ablation process separately for finger and busbar openings. Finally, it is demonstrated that the use of higher laser fluences does not impact the electrical performance of the Al back surface field cells, with open-circuit voltages of ≥637 mV and fill factors ≥80.4% being demonstrated for cells where the average laser fluence used was varied between 0.35 and 0.63 J/cm2.

SEASONAL MONITORING ELECTROMAGNETIC SITUATION IN THE RADIO-FREQUENCY RANGE OF MOBILE COMMUNICATION

Introduction. The study of the electromagnetic environment created by mobile communication terminals (MCT) is one of the important tasks of modern preventive medicine. In the study, the assessment of the electromagnetic environment created by MCT according to fluence values. Material and methods. The fluence level of MCT radiation was determined in the territory of the Crimea using a mobile monitoring system. The number of paired (seasonally) fluence measurement points accounted for 2102. At each point, the level of electromagnetic radiation (EMR) was determined sequentially from two identical MP (Samsung G3) in voice mode with the remote subscriber. Results. The average fluence value in Crimea for the year amounted to 1.45 ± 0.06 μW/cm2. In the winter (non-resort) season fluence accounted for 1.34 ± 0.05 µW/cm2, in the summer (resort) season -1.54 ± 0.05 µW/cm2. A comparative non-parametric analysis of the winter and summer fluence values in the resort regions revealed significant differences, whereas in non-resort regions there were no significant differences. Obtained as a result of monitoring of the electromagnetic situation, the data showed significant heterogeneity of fluence by administrative units within the Republic of Crimea from 0.92 ± 0.03 in the Belogorskiy to 2.11 ± 0.07 μW/cm2 in the Chernomorsky regions, which indicates the difference in mobile coverage areas in Crimea. Significant differences between the fluence values obtained in the winter and summer seasons for resort regions can be explained by the uneven workload of base stations due to the seasonal dynamics of the influx of tourists. Conclusion. As a result of the work done, an average annual fluence value of 1.45 ± 0.06 µW/cm2 was obtained, its considerable heterogeneity and reliable seasonal changes were revealed. Keywords: seasonal monitoring; cell phone; fluence.

Damage studies on irradiated tungsten by helium ions in a plasma focus device

Abstract Damage of tungsten due to helium ions of a PF device was studied. The tungsten was analyzed by SEM and AFM after irradiation. SEM revealed fine bubbles of helium atoms with diameters of a few nanometers, which join and form larger bubbles and blisters on the surface of tungsten. This observation confirmed the results of molecular dynamics simulation. SEM analysis after etching of the irradiated surface indicated cavities with depth range of 35–85 nm. The average fluence of helium ion of the PF device was calculated about 5.2 × 1015 cm−2 per shot, using Lee code. Energy spectrum of helium ions was estimated using a Thomson parabola spectrometer as a function of dN/dE ∝ E−2.8 in the energy range of 10–200 keV. The characteristics of helium ion beam was imported to SRIM code. SRIM revealed that the maximum DPA and maximum helium concentration occur in the depth range of 20–50 nm. SRIM also showed that at depth of 30 nm, all of the tungsten atoms are displaced after 20 shots, while at depth of higher than 85 nm the destruction is insignificant. There is a close match between SRIM results and the measured depths of cavities in SEM images of tungsten after etching.

Microplasma UV lamp as a new source for UV-induced water treatment: Protocols for characterization and kinetic study

The newly emerged microplasma UV radiating technology can be a viable alternative to conventional radiation sources for UV water treatment. The capability of the microplasma UV lamp to monochromatically irradiate various wavelengths with different pulsation frequencies in a flat form opens new pathways for the development of novel UV-based water purifiers. This study is the first to systematically examine the microplasma UV lamp and develop a robust experimental method and apparatus for its operation to study the kinetics of both microbial and chemical pollutant degradation. The microplasma UV lamp was characterized in terms of its radiation profile and the impact of operating parameters on the lamp radiant power output. It was shown to be an instant-on and fast stabilized source. The radiant power output was a linear function of the electrical current and was not influenced by the lamp operating temperature and intermittent on/off cycles. A protocol was developed for obtaining reliable kinetic data for UV-induced elimination of microorganisms and micropollutants. An experimental setup was proposed for the kinetic studies, where the characteristics of the incident irradiance of the lamp, including uniformity, collimation, and divergence, were quantitatively evaluated. In addition, the water factor (WF) for calculating the average fluence rate was redefined for both the transient and steady state conditions. This modification is essential to account for changes in the UV transmittance of the medium, which could be an important factor for kinetic study of chemical contaminants. Two studied cases of microbial direct inactivation and the chemical photo-initiated oxidation process in different setups, based on the developed protocol, confirmed the reproducibility of the fluence-based kinetic data independent of the reactor size. The proposed protocol can be applied to the kinetic study of the elimination of microbial and chemical contaminants using microplasma UV lamps of any size, power, and peak wavelength.

Controllable fabrication of polygonal micro and nanostructures on sapphire surfaces by chemical etching after femtosecond laser irradiation

We fabricate two different types of micro and nanostructures with either pyramid-like or tetrahedron-like geometry on the sapphire surface, through the use of thechemical etching process after femtosecond laser irradiation. The distinct features of the structures are measured with both scanning electron microscopy and atomic force microscopy. The dynamic regions for the formation of the two surface structures are experimentally obtained to indicate their tunability by varying the laser average fluence and etching temperature. With the help of discussions and analyses, we propose a model to explain the formation mechanisms of the two kinds of structures, in which the competition between the growth of the alunogen (Al2 (SO4)3·17H2O) crystals and the anisotropic etching rate of the sapphire material plays an important role. In addition, it is confirmed that the tetrahedron-like structures can be used to activate the sapphire substrate for the enhancement of Raman scattering and the hydrophobic properties.

Influence of a Femtosecond Laser Surface Modification on the Fatigue Behavior of Ti-6Al-4V ELI Alloy

The objective of this investigation was to evaluate the influence of surface modification by femtosecond laser (with average fluence of 0.6 J/cm2 and scanning speed of 0.1 mm/s) on the fatigue resistance of Ti-6Al-4V ELI alloy. A significant reduction in the fatigue strength of the material modified by laser was observed. Residual tensile stresses generated during surface modification were negligible, presenting lower values than those found on the unmodified surface. Based on a recently developed and published prediction model, the reduction of the fatigue strength was ascribed to the surface roughness created during the laser treatment of the alloy. An evidence was that the fatigue crack nucleation occurred in the modified region, rather than at the edge of the rectangular specimens as in the untreated condition.

Bidirectional ring amplifier with twin pulses for high-power lasers.

A novel bidirectional ring amplifier with twin pulses for high-power lasers is proposed, and the performances on output energy capability and extraction efficiency are comprehended with detailed simulation. The results show that an extraction efficiency of 62.3% and the output energy of 13.4 kJ per pulse at the B integral limit can be obtained at low average fluence of 10.3 J/cm2 and the low injection energy of 3.9 mJ in the bidirectional ring amplifier. Compared with the multi-pass amplifier, the bidirectional ring amplifier is more compact and the extraction efficiency is much higher at low injection energy and low laser fluence operation, which is beneficial to simplify the preamplifier system and reduce the effects of nonlinear phase shift.