- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Demonstration of Femtosecond Broadband X-rays from Laser Wakefield Acceleration as a Source for Pump-Probe X-ray Absorption Studies
摘要： We present X-ray absorption measurements near the K-edge of laser heated aluminum in a pump-probe configuration using X-rays generated in a laser wakefield accelerator. A 30 fs duration laser pulse from the Hercules laser system was split into two beam lines, with one used to heat a 4 μm thickness Al foil and the second to drive a laser wakefield accelerator. The laser-heated plasma was probed at various pump-probe delays using the femtosecond duration X-rays generated by betatron oscillations of the electrons in the wakefield. We observe an apparent blue-shift of the K-edge occurring on a sub-picosecond timescale in the transmission spectra.
关键词： Broadband X-rays,X-ray Absorption Studies,Femtosecond,Laser Wakefield Acceleration,Pump-Probe
更新于2025-09-12 10:27:22
-
Surface polishes of the SKD 61 tool steel by a femto pulse laser operating in a wide range of powers
摘要： SKD 61 tool steel workpieces without prior heat treatment are adopted for pulse femto laser polish with the power in a range of 0.1-20 mW. Single-pass tracks are provided first to evaluate the width (W) and depth (D) of groove's lateral profile. With the characteristics exhibited in the nearly constant D/W data and the noticeable changes in the crystal species and the Fe content in this powers range, the three power subregions and the powers required for the solid-(plasma) ablation and the ablation-evaporation plus plasma breakdown transitions can be identified clearly. Surfaces polished with 0, 50, and 70 % as the overlap ratio are presented to investigate the mean areal roughness (Sa) and the highest roughness amplitude (HA) transition, (Sa)0% >> (Sa)50% > (Sa)70% is presented. When the power is applied beyond the threshold (14 mW, 1.7224 J/cm2) for material evaporation and plasma breakdown, affected by the laser fluence (F) in these three subregions and the overlap ratio. As power is applied below the solid-ablation transition (9~10 mW, F: 1.3777~1.5239 J/cm2), (Sa)0% >> (Sa)70% > (Sa)50% is obtained; if it is applied higher than this frequency analysis; phase transformation.
关键词： D/W ratio,femtosecond laser polishing,phase transformation,spatial frequency analysis,ablation threshold
更新于2025-09-12 10:27:22
-
Femtosecond Laser Implantation of a 355-Degree Intrastromal Corneal Ring Segment in Keratoconus: A Three-Year Follow-Up
摘要： Purpose. To evaluate the outcomes of femtosecond laser-assisted implantation of a 355-degree intracorneal ring (ICR) (Keraring) in patients with keratoconus in the three-year follow-up. Setting. Future Femtolaser Center, Sohag, Egypt. Design. Prospective interventional case series. Patients and Methods. A prospective case series of 38 eyes of 26 patients with keratoconus had implantation of the 355-degree ICR keraring after tunnel creation with a femtosecond laser. The uncorrected visual acuities (UCVA) and best-corrected visual acuities (BCVA), sphere, cylinder, and manifest refraction spherical equivalent (SE), and mean keratometry (K), K max, and K min were evaluated preoperatively and 3, 6, 12, 24, and 36 months postoperatively, and all complications were reported. Results. 38 eyes of 26 patients with mean age 25.92 ± 5.44 years were enrolled in the study, 11 were males (42.3%). The mean UCVA improved from 0.93 ± 0.21 to 0.63 ± 0.21 logMAR (P ≤ 0.001) and the mean BCVA from 0.67 ± 0.22 to 0.43 ± 0.26 logMAR (P < 0.001). The mean sphere, cylinder, and spherical equivalent have been changed dramatically from preoperative to 3 month postoperative, which is statistically signi?cant (P ≤ 0.001), and the changes between 1 and 2 years and 2 and 3 years are also considerable and statistically signi?cant; the K max and K min and K mean improved and the changes were statistically signi?cant (P ≤ 0.001), and the changes between one, two, and three years were also statistically signi?cant. The safety and e?cacy indices were changed through the three-year follow-up. The complications were corneal neovascularization (36.84%), corneal melting (26.3%), and ring extrusion (31.5%) at the end of the study. Conclusions. Implantation of a 355-degree intracorneal keraring using femtosecond laser improved the visual, refractive, and topographic parameters in keratoconus patients, with a high rate of ICR extrusion and instability. The study has been registered for the Pan African Clinical Trial Registry (http://www.pactr.org) database within No: PACTR201810796878908 on 29 October 2018.
关键词： keratoconus,Keraring,refractive error,femtosecond laser,visual acuity,corneal topography,intracorneal ring
更新于2025-09-12 10:27:22
-
Ultrafast Melting of Metal–Organic Frameworks for Advanced Nanophotonics
摘要： The conversion of metal–organic frameworks (MOFs) into derivatives with a well-defined shape and composition is considered a reliable way to produce efficient catalysts and energy capacitors at the nanometer scale. Yet, approaches based on conventional melting of MOFs provide the derivatives such as amorphous carbon, metal oxides, or metallic nanoclusters with an appropriate morphology. Here ultrafast melting of MOFs is utilized by femtosecond laser pulses to produce a new generation of derivatives with complex morphology and enhanced nonlinear optical response. It is revealed that such a nonequilibrium process allows conversion of interpenetrated 3D MOFs comprising flexible ligands into well-organized spheres with a metal oxide dendrite core and amorphous organic shell. The ability to produce such derivatives with a complex morphology is directly dependent on the electronic structure, crystal density, ligand flexibility, and morphology of initial MOFs. An enhanced second harmonic generation and three-photon luminescence are also demonstrated due to the resonant interaction of 100–1000 nm spherical derivatives with light. The results obtained are in the favor of new approaches for melting special types of MOFs for nonlinear nanophotonics.
关键词： ultrafast melting,femtosecond laser,nanophotonics,metal–organic framework,derivatives
更新于2025-09-12 10:27:22
-
Femtosecond Laser-Assisted Keratolimbal Allograft Transplantation for the Treatment of Total Limbal Stem Cell Deficiency
摘要： To investigate the surgical procedure and therapeutic efficacy of femtosecond (FS) laser-assisted keratolimbal allograft (KLAL) transplantation in the treatment of eyes with total limbal stem cell deficiency. Methods: Ten eyes from 10 patients who underwent FS laser-assisted KLAL transplantation were enrolled. The best-corrected visual acuity (BCVA), ocular surface stability, corneal transparency, and postoperative complications were recorded. Results: The keratolimbal grafts prepared using the FS laser were even in thickness and width. After the surgery, glucocorticoid and tacrolimus eye drops were administered locally to the eyes with concentration gradients, and a medium dose was prescribed for maintenance. Within the mean follow-up period of 16.8 6 7.3 months, 9 of 10 eyes (90.0%) maintained a stable ocular surface and showed significant transparency and improvements in corneal BCVA. Persistent corneal edema only occurred in one eye because of repeated epithelial defects, and the BCVA of this eye did not improve. Confocal microscopy revealed activated dendritic cells in the Bowman membrane at the limbus, but they were always low in density with small dendritic processes. No acute immune rejection, cataracts, or elevation of intraocular pressure were detected. Conclusions: The FS laser-assisted KLAL technique can produce ring-shaped grafts with an even depth and width, resulting in a stable ocular surface and good visual prognosis. After surgery, glucocorticoids and potent immunosuppressive eye drops were administered locally with concentration gradients and effectively inhibited acute immune rejection.
关键词： femtosecond laser,limbal stem cell deficiency,keratolimbal allograft
更新于2025-09-12 10:27:22
-
Formation Dynamics of Excited Neutral Nitrogen Molecules inside Femtosecond Laser Filaments
摘要： Nitrogen molecules are promoted to excited neutral states during femtosecond laser pulse filamentary propagation in atmosphere, leading to a characteristic UV fluorescence. Using a laser-induced fluorescence depletion technique, we measure the formation dynamics of these excited neutral nitrogen molecules with femtosecond time resolution. We find that the excited neutral molecules are formed in an unexpected ultrafast timescale of ～4 ps at 1 bar and ～120 ps at 30 mbar pressure. From this observation we deduce that the excitation of neutral N2 occurs via multiple collisions with hot free electrons. Numerical simulations based on rate equations reproduce well this ultrafast formation time and its dependence on gas pressure, and thus support this interpretation.
关键词： electron impact excitation,femtosecond laser,plasma filament,UV fluorescence,nitrogen molecules
更新于2025-09-12 10:27:22
-
Femtosecond-laser-written optofluidics in alumino-borosilicate glass
摘要： Femtosecond Laser Irradiation followed by Chemical Etching (FLICE) is a powerful technique for prototyping three-dimensional microfluidic structures in glass. Direct inscription of optical waveguides, by the same femtosecond laser, enables rapid fabrication of optofluidic devices for chemistry or biology applications. As a matter of fact, substrates where FLICE is known as most effective, such as fused silica, are not optimal for laser inscription of high-contrast optical waveguides, thus limiting the potentials of this technology. Here we show that it is possible to apply FLICE also to a commercial alumino-borosilicate glass, where very complex and low-loss photonic circuitry has been demonstrated recently. Besides optimizing the irradiation parameters to achieve hollow structures with high aspect-ratio, we investigate the etching dynamics and the micro-morphology of the etched regions. As a test for the technique, we realize an optofluidic device composed of a microchannel and two intersecting optical waveguides.
关键词： Borosilicate glass,Microfluidics,Femtosecond laser micromachining
更新于2025-09-12 10:27:22
-
Ultrafast electron transfer through silicon-vacuum interface induced by the action of intense femtosecond laser pulse
摘要： A theoretical study of the influence of a quasistationary electric field formed during emission separation of charges on ultrafast electron transfer near the silicon-vacuum interface irradiated by femtosecond laser pulses was carried out. The values of the strength of the arising quasistationary field during irradiation by femtosecond pulses with fluences near and above the silicon damage thresholds were estimated. The possibility of the formation of a dynamic optically layered structure in the near-surface layers of silicon irradiated by a femtosecond pulse resulting from a modification of its optical properties due to the depletion of electrons in the surface layer was studied. It is suggested that the time-depending dipole moment induced by the emission separation of charges should lead to the generation of electromagnetic radiation from the terahertz frequency range. The basic properties of this radiation were theoretically investigated.
关键词： Coulomb explosion,silicon,ultrafast heating,terahertz radiation,electron emission,electron transfer,femtosecond laser pulse
更新于2025-09-12 10:27:22
-
Prediction of femtosecond laser ablation parameter on Human teeth using chemical compositional analysis
摘要： Laser-based tooth preparation is an emerging non-invasive technique in dentistry. The knowledge about laser ablation parameters is essential for precise removal of lesion or damaged part of the tooth. The present study introduced a novel technique to determine key laser ablation parameters using elemental analysis so that the clinician can readily obtain the optimized laser processing condition. In pursuance of correlating ablation parameters with elemental composition of teeth, a large elemental variation is induced on the dentin and enamel surface by pretreatment using orthophosphoric acid and Carie care gel. The pretreated enamel and dentin surface were irradiated by 800 nm, 100 fs, Ti:Sapphire laser and the elemental analysis were carried out by EDS. Threshold fluence shows the negative correlation with carbon element (C) and shows a positive correlation with Ca and P whereas the converse is true for effective Gaussian beam radius and effective energy penetration depth. The Ca, P and C show good linearity with all ablation parameters. Despite high sensitivity of C, both Ca and P can be the most reliable probe to predict the laser ablation parameters. The method present a simple and straightforward tool to optimize the laser parameter from the non-destructive evaluation of chemical composition even in case of tooth complexity (age, sex and race). In essence, the chemical composition analysis by a suitable probe will improve the precision of laser surgery and reduce the tissue damage in clinical use.
关键词： dentin,Femtosecond laser ablation,enamel,teeth compositional analysis,ablation parameters
更新于2025-09-12 10:27:22
-
[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - THz response of metallic structures to femtosecond laser pulses
摘要： The talk is devoted to the nonlinear effects in metallic structures (like gratings and nanoparticle arrays) irradiated by femtosecond laser pulses. Possible mechanisms of delayed THz response and specific non-quadratic nonlinear regimes of conversion are analyzed. In contrast to previous models, only low-frequency currents inside the metal are considered without involving electron emission and acceleration. Special attention is paid to the role of plasmonic resonances at optical frequency in the enhancement of low-frequency nonlinear response.
关键词： femtosecond laser pulses,plasmonic resonances,metallic structures,nonlinear effects,THz response
更新于2025-09-12 10:27:22