Structure-Mediated Excitation of Air Plasma and Silicon Plasma Expansion in Femtosecond Laser Pulses Ablation

Femtosecond laser-induced surface structures upon multiple pulses irradiation are strongly correlated with the pulse number,which in turn significantly affects successive laser-material interactions. By recording the dynamics of femtosecond laser ablation of silicon using time-resolved shadowgraphy, here we present direct visualization of the excitation of air plasma induced by the reflected laser during the second pulse irradiation.The interaction of the air plasma and silicon plasma is found to enhance the shockwave expansion induced by silicon ablation in the longitudinal direction, showing anisotropic expansion dynamics in different directions. We further demonstrate the vanishing of air plasma as the pulse number increases because of the generation of a rough surface without light focusing ability. In the scenario, the interaction of air plasma and silicon plasma disappears; the expansion of the silicon plasma and shockwave restores its original characteristic that is dominated by the laser-material coupling.The results show that the excitation of air plasma and the laser-material coupling involved in laser-induced plasma and shockwave expansion are structure mediated and dependent on the pulse number, which is of fundamental importance for deep insight into the nature of laser-material interactions during multiple pulses ablation

Structure-Mediated Excitation of Air Plasma and Silicon Plasma Expansion in Femtosecond Laser Pulses Ablation

Femtosecond laser-induced surface structures upon multiple pulses irradiation are strongly correlated with the pulse number, which in turn significantly affects successive laser-material interactions. By recording the dynamics of femtosecond laser ablation of silicon using time-resolved shadowgraphy, here we present direct visualization of the excitation of air plasma induced by the reflected laser during the second pulse irradiation. The interaction of the air plasma and silicon plasma is found to enhance the shockwave expansion induced by silicon ablation in the longitudinal direction, showing anisotropic expansion dynamics in different directions. We further demonstrate the vanishing of air plasma as the pulse number increases because of the generation of a rough surface without light focusing ability. In the scenario, the interaction of air plasma and silicon plasma disappears; the expansion of the silicon plasma and shockwave restores its original characteristic that is dominated by the laser-material coupling. The results show that the excitation of air plasma and the laser-material coupling involved in laser-induced plasma and shockwave expansion are structure mediated and dependent on the pulse number, which is of fundamental importance for deep insight into the nature of laser-material interactions during multiple pulses ablation

Femtosecond UV Laser Ablation Characteristics of Polymers Used as the Matrix of Astronautic Composite Material

Ultrafast laser processing has recently emerged as a new tool for processing fiber-reinforced polymer (FRP) composites. In the astronautic industry, the modified epoxy resin (named 4211) and the modified cyanate ester resin (known as BS-4) are two of the most widely used polymers for polymer-based composites. To study the removal mechanism and ablation process of different material components during the ultrafast laser processing of FRPs, we isolated the role of the two important polymers from their composites by studying their femtosecond UV laser (260 fs, 343 nm) ablation characteristics for controllable machining and understanding the related mechanisms. Intrinsic properties for the materials’ transmission spectrum, the absorption coefficient and the optical bandgap (Eg), were measured, derived, and compared. Key parameters for controllable laser processing, including the ablation threshold (Fth), energy penetration depth (δeff), and absorbed energy density (Eabs) at the ablation threshold, as well as their respective “incubation” effect under multiple pulse excitations, were deduced analytically. The ablation thresholds for the two resins, derived from both the diameter-regression and depth-regression techniques, were compared between resins and between techniques. An optical bandgap of 3.1 eV and 2.8 eV for the 4211 and BS-4 resins, respectively, were obtained. A detectable but insignificant-to-ablation difference in intrinsic properties and ablation characteristics between the two resins was found. A systematic discrepancy, by a factor of 30~50%, between the two techniques for deriving ablation thresholds was shown and discussed. For the 4211 resin ablated by a single UV laser pulse, a Fth of 0.42 J/cm2, a δeff of 219 nm, and an Eabs of 18.4 kJ/cm3 was suggested, and they are 0.45 J/cm2, 183 nm, and 23.2 kJ/cm3, respectively, for the BS-4 resin. The study may shed light on the materials’ UV laser processing, further the theoretical modeling of ultrafast laser ablation, and provide a reference for the femtosecond UV laser processing characteristics of FRPs for the future

Predictive value of thromboelastography for postoperative lower extremity deep venous thrombosis in gastric cancer complicated with portal hypertension patients

Background To explore the predictive value of thromboelastography (TEG) for the occurrence of lower extremity deep venous thrombosis (LDVT) in gastric cancer combined with portal hypertension patients after operation. Methods 172 gastric cancer patients combined with portal hypertension were randomly divided into laparoscopic surgery or laparotomy groups. All patients were taken venous blood on an empty stomach 1 day before operation, 1 day, 3 days, and 5 days after operation. Results There was no significant difference in R value, K value, α angle, and MA before and after operation (P > .05). Compared with the same group before operation, the R value and K value were decreased at 1, 3, and 5 days after operation, while the α angle and MA were increased (P < .05). Compared with the non-LDVT group, the postoperative R value and K value in the LDVT group were significantly lower, while the α angle and MA were significantly higher (P < .05). The AUC of R value, K value, α angle, and MA levels at 3 days after surgery to identify patients with LDVT was 0.778, 0.718, 0.881, and 0.781, respectively. The estimated probability of the final model for LDVT was 0.622. Compared with the estimated probability ≥0.622 group, the LDVT rate in the estimated probability <0.622 group was significantly increased (χ2 = 60.128, P < .001). Conclusions The combination of R value, K value, α angle, and MA at 3 days after surgery has a moderately effective predictive effect for the occurrence of LDVT in gastric cancer patients combined with portal hypertension

Enhancement of ablation and ultrafast electron dynamics observation of nickel-based superalloy under double-pulse ultrashort laser irradiation

Temporally shaped femtosecond laser machining is a flexible and effective method to improve the efficiency and quality of cooling film holes. This study investigated the ablation of nickel-based superalloy by double-pulse femtosecond laser with different pulse-separations and fluences. Compared with single-pulse ablation, approximate 1.5 times enhancement of ablation area was obtained in double-pulse ablation with about 2 ps pulse-separation. By varying the pulse-separations, the ablation area can be tuned, and at the same time, the ablation depth can be kept for little fluctuation. An improved two-temperature model and time-resolved transient reflectivity technique were used for analyzing the ablation mechanisms. We found that more energy deposition can happen from electron system to lattice system for double-pulse ablation, which makes ablation area increase. However, mechanical relaxation started at around 2 ps, which could be suppressed by the pressure wave induced by the second sub-pulse, and finally achieved the maximum ablation area at about 2 ps pulse-separation. Besides, laser-induced subwavelength periodic surface structures were observed under irradiation of multiple pulses. The findings may aid in understanding the ablation mechanism between nickel-based superalloy and femtosecond laser, as well as in optimizing the processing of cooling film holes

Structure-Mediated Excitation of Air Plasma and Silicon Plasma Expansion in Femtosecond Laser Pulses Ablation

Femtosecond laser-induced surface structures upon multiple pulses irradiation are strongly correlated with the pulse number,which in turn significantly affects successive laser-material interactions. By recording the dynamics of femtosecond laser ablation of silicon using time-resolved shadowgraphy, here we present direct visualization of the excitation of air plasma induced by the reflected laser during the second pulse irradiation.The interaction of the air plasma and silicon plasma is found to enhance the shockwave expansion induced by silicon ablation in the longitudinal direction, showing anisotropic expansion dynamics in different directions. We further demonstrate the vanishing of air plasma as the pulse number increases because of the generation of a rough surface without light focusing ability. In the scenario, the interaction of air plasma and silicon plasma disappears; the expansion of the silicon plasma and shockwave restores its original characteristic that is dominated by the laser-material coupling.The results show that the excitation of air plasma and the laser-material coupling involved in laser-induced plasma and shockwave expansion are structure mediated and dependent on the pulse number, which is of fundamental importance for deep insight into the nature of laser-material interactions during multiple pulses ablation

Femtosecond Laser Processing Structural Surfaces of Zinc anodes for rechargeable zinc-air battery

Researches about renewable rechargeable battery have attracted the attention of many scholars, due to increasing demands of energy and global energy crisis. Zinc-air batteries are one of most promising energy sources, but the morphological changes and forming dendritic of zinc anodes greatly limit their cycle life during the charging-discharging process. In order to improve zinc-air batteries electrochemical performance and control dendritic growth, surface of zinc anodes is irradiated by femtosecond laser with different power. The electrochemical results indicate that zinc anodes of zinc-air batteries with different surface structures show different electrochemical properties. Due to the removing oxide layer on the surface of zinc anode, adding contact areas of zinc anodes and electrolytes, and restraining dendritic growth by femtosecond laser processing, first discharge time of zinc anodes with surface structures of zinc-air batteries is about 10 times than that of without processing. It is also found that more intense chemical reactions occur in the area treated by femtosecond laser

A fatal case of liver abscess caused by hypervirulent Klebsiella pneumoniae in a diabetic adolescent: A clinical and laboratory study

ABSTRACT Importance Hypervirulent variants of Klebsiella pneumoniae (hvKp) are capable of causing life‐threatening pyogenic liver abscesses (PLAs), but hvKp caused PLAs was seldom reported in pediatric populations. Hence, there is an urgent need to raise our awareness of this phenomenon in pediatric populations. Objective This study aimed to report the clinical characteristics of hvKp that caused fatal PLA complicated by bacteremia in an adolescent and further identify the microbiological and genomic features of the causative strain. Methods A 14‐year‐old boy with diabetes mellitus was admitted to our hospital with a diagnosis of PLA complicated by bacteremia. A hypermucoviscous hvKp strain, KPN_19‐106, was isolated from the drainage fluid present within the liver abscess cavity and blood. The hypermucoviscosity phenotype of the causative strain was determined by string test. Its virulence was measured using serum resistance assay and Galleria mellonella larvae‐killing assay. Antimicrobial susceptibility was determined by broth microdilution method. Genetic information was obtained by whole‐genome sequencing and bioinformatics analysis. Results KPN_19‐106 belonged to sequence type 380 and serotype K2 and exhibited stronger serum resistance and higher in vivo lethality than the well‐characterized hvKp NTUH‐K2044 strain. Although KPN_19‐106 is susceptible to most antibiotics, no sign of improvement was observed during treatment with such drugs. Whole‐genome sequencing revealed that the isolate had integrated multiple mobile genetic elements related to virulence. Interpretation Antibiotic‐susceptible hvKp can cause fatal PLA complicated by bacteremia in adolescents, with no improvement during antimicrobial therapy. The causative strain in this case had integrated multiple virulence genes and thus exhibited higher virulence both in vitro and in vivo when compared with NTUH‐K2044

Directed energy deposition combining high-throughput technology and machine learning to investigate the composition-microstructure-mechanical property relationships in titanium alloys

Traditional approaches to alloy design, such as “trial-and-error” experiments, are costly and time-consuming in developing titanium alloys (and other alloys as well) for various requirements. Herein, we present a high-throughput technology combining the Directed energy deposition (DED) process and machine learning to elucidate the composition-microstructure-mechanical property relationships of DED new Ti-Al-V alloys. A total of 144 sets of ternary Ti-xAl-yV (0 ≤ x ≤ 11, 0 ≤ y ≤ 11, all in wt %) alloys were synthesized by DED, and the microstructure, microhardness, and yield strength of the alloys were rapidly characterized through image processing methods and instrumented micro-indentation. Backpropagation (BP) neural network models were developed to determine the microstructure parameters (average width of α-laths, Wα, and volume fraction of α-phase, Vα), microhardness, and yield strength as a function of the composition of DED Ti-Al-V alloys. The results showed that the Vα increases linearly with increasing Al content and decreases with increasing V content. However, a nonlinear relationship between Wα and contents of Al and V was found, which is mainly responsible for the nonlinear relationship between mechanical properties and composition. The approach established in this work can shed insight into developing alloys suitable for additive manufacturing