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Cylindrical and plane surface electromagnetic waves in laser technology of silicon surface texturing with a double femtosecond pulse
摘要： This paper presents experimental results of laser modification of the surface of monocrystalline silicon under the influence of a double femtosecond laser pulse with varying delays less than or close to the electron–phonon interaction time, as well as the results of numerical simulation of the photoexcitation of a semiconductor in the approximation of dielectric constant. It is shown that the excitation of cylindrical surface waves not only precedes the excitation of plane surface electromagnetic waves, but is also a determining factor in the cumulative change in the dielectric constant of the medium and the creation of conditions for the excitation of plane surface electromagnetic waves.
关键词： Femtosecond texturing of the surface,Cylindrical surface electromagnetic waves,Monocrystalline silicon,Surface electromagnetic waves,Double femtosecond laser pulse
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Terahertz Wave Generation in Air by Femtosecond Optical Vortex Pulses
摘要： Terahertz (THz) radiation is of great current interest due to many applications such as nonlinear THz spectroscopy and imaging. One of the compact and effective methods to obtain very high THz field strengths and extremely broadband spectral widths is THz wave generation from plasma filaments formed in air by focused bichromatic femtosecond laser pulses consisting of the first and the second harmonics (FH, SH). Here we investigate the effect of an azimuthal phase modulation of the SH carrying an optical vortex charge on the intensity and phase distribution of the THz pulse emitted from the laser induced plasma filament in air. We present both experimental and theoretical results.
关键词： Terahertz radiation,plasma filaments,femtosecond optical vortex pulses,bichromatic femtosecond laser pulses
更新于2025-09-11 14:15:04
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Femtosecond Laser Lift‐Off with Sub‐Band Gap Excitation for Production of Free‐Standing GaN LED Chips
摘要： A novel method for lifting-off GaN-based LED structures from sapphire substrates is demonstrated. In this approach, ultrashort (350 fs) green pulses are scanned across the sample backside to lift-off the LED, utilizing two-photon absorption at the GaN/sapphire interface. The corresponding fluence regime is carefully investigated. Stable emission properties after laser lift-off are proven by cathodoluminescense measurements.
关键词： GaN,light-emitting diode,femtosecond laser,non-linear optics,laser lift-off
更新于2025-09-11 14:15:04
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High-Intensity Laser Irradiation Inducing Au Nanoparticles in Viscous Glycerin
摘要： We studied the formation of gold nanoparticles (Au NPs) by laser-induced nucleation from HAuCl4 in viscous glycerin (η = 1,400 mPa s) at a room temperature for the application of laser-drilled screen printing. Femtosecond pulsed laser irradiation at a wavelength of 800 nm and a pulse energy of 5 mJ caused Au NPs with a mean diameter of 4.9 nm at a concentration of 2.5×10-5 mol dm-3. The decrease in viscosity by heating the solution at 313 K and the mechanical stirring of the solution during laser irradiation caused the mean diameter and size distribution to become small. The mechanical stirring was effective for the formation of uniform Au NPs with a mean diameter of 3.2 nm. These indicated that successive pulsed laser irradiation induced uniform nucleation reactions of HAuCl4 to metal Au, melting and fusion among metal Au species, and particle growth through Ostwald ripening. The Au NPs formed in glycerin kept a suspension for at least 1 week without any stabilizing surfactants probably due to low frequency of contacting NPs in viscous glycerin.
关键词： Au,viscous solution,femtosecond laser,nanoparticle,laser-induced nucleation
更新于2025-09-11 14:15:04
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In-Situ and Ex-Situ Characterization of Femtosecond Laser-Induced Ablation on As2S3 Chalcogenide Glasses and Advanced Grating Structures Fabrication
摘要： Femtosecond laser pulse of 800 nm wavelength and 150 fs temporal width ablation of As2S3 chalcogenide glasses is investigated by pump-probing technology. At lower laser fluence (8.26 mJ/cm2), the surface temperature dropping to the melting point is fast (about 43 ps), which results in a clean hole on the surface. As the laser fluence increases, it takes a longer time for lattice temperature to cool to the melting point at high fluence (about 200 ps for 18.58 mJ/cm2, about 400 ps for 30.98 mJ/cm2). The longer time of the surface heating temperature induces the melting pool in the center, and accelerates material diffusing and gathering surrounding the crater, resulting in the peripheral rim structure and droplet-like structure around the rim. In addition, the fabricated long periodic As2S3 glasses diffraction gratings can preserve with high diffraction efficiency by laser direct writing technology.
关键词： femtosecond laser,laser processing
更新于2025-09-11 14:15:04
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Clinical outcomes of small incision lenticule extraction versus femtosecond laser-assisted LASIK for myopia: a Meta-analysis
摘要： ● AIM: To evaluate the possible differences in visual quality between small incision lenticule extraction (SMILE) and femtosecond laser in situ keratomileusis (FS-LASIK) for myopia. ● METHODS: A Meta-analysis was performed. Patients were from previously reported comparative studies treated with SMILE versus FS-LASIK. The PubMed, EMBASE, Cochrane, Web of Science and Chinese databases (i.e. WANFANG and CNKI) were searched in Nov. of 2016 using RevMan 5.1 version software. The differences in visual acuity, aberration and biomechanical effects within six months postoperatively were showed. Twenty-seven studies including 4223 eyes were included. ● RESULTS: No significant differences were observed between SMILE and FS-LASIK in terms of the proportion of eyes that lost one or more lines of corrected distance visual acuity after surgery (P=0.14), the proportion of eyes achieving an uncorrected distance visual acuity of 20/20 or better (P=0.43), the final refractive spherical equivalent (P=0.89), the refractive spherical equivalent within ±1.00 diopter of the target values (P=0.80), vertical coma (P=0.45) and horizontal coma (P=0.06). Compared with the FS-LASIK group, total higher-order aberration (P<0.001) and spherical aberration (P<0.001) were higher and the decrease in corneal hysteresis (P=0.0005) and corneal resistance factor (P=0.02) were lower in the SMILE group. ● CONCLUSION: SMILE and FS-LASIK are comparable in efficacy, safety and predictability for correcting myopia.
关键词： Meta-analysis,small incision lenticule extraction,myopia,femtosecond laser in situ keratomileusis
更新于2025-09-11 14:15:04
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Femtosecond Laser Fabrication of Stable Hydrophilic and Anti-Corrosive Steel Surfaces
摘要： We report on a novel single-step method to develop steel surfaces with permanent highly hydrophilic and anti-corrosive properties, without employing any chemical coating. It is based on the femtosecond (fs) laser processing in a saturated background gas atmosphere. It is particularly shown that the fs laser microstructuring of steel in the presence of ammonia gas gives rise to pseudoperiodic arrays of microcones exhibiting highly hydrophilic properties, which are stable over time. This is in contrast to the conventional fs laser processing of steel in air, which always provides surfaces with progressively increasing hydrophobicity following irradiation. More importantly, the surfaces subjected to fs laser treatment in ammonia exhibit remarkable anti-corrosion properties, contrary to those processed in air, as well as untreated ones. The combination of two functionalities, namely hydrophilicity and corrosion resistance, together with the facile processing performed directly onto the steel surface, without the need to deposit any coating, opens the way for the laser-based production of high-performance steel components for a variety of applications, including mechanical parts, ?uidic components and consumer products.
关键词： femtosecond laser processing,wettability,steel,anticorrosion
更新于2025-09-11 14:15:04
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Novel Triamcinolone Acetonide-Loaded Liposomal Topical Formulation Improves Contrast Sensitivity Outcome After Femtosecond Laser-Assisted Cataract Surgery
摘要： Purpose: To assess visual results, macular modi?cations, and the incidence of clinically signi?cant macular edema (CSME) in patients using a topical triamcinolone acetonide-loaded liposomal formulation (TA-LF) after femtosecond laser-assisted cataract surgery (FLACS). Methods: Fifty-six eyes after FLACS were selected. Twenty-eight eyes in the combined therapy group (P + N) were treated with prednisolone 1% and nepafenac 0.1% for 21 days postoperatively, whereas 28 eyes in the TA-LF group received a liposomal formulation containing 2 mg/mL of TA (0.2%) for the same period of time. Follow-up visits at 1 day, 6 weeks, and 12 weeks after surgery consisted of visual acuity, contrast sensitivity (CS), central foveal thickness (CFT), total macular volume (TMV) measurements, and the detection of CSME. Results: CS improved in the TA-LF group (basal value: 1.087 – 0.339 vs. 1.276 – 0.147 at week 12, P = 0.0346), whereas in the P + N group, CS was not different from the baseline (basal value: 1.130 – 0.331 vs. 1.274 – 0.133 at week 12, P = 0.1276). There were similar increases in postoperative CFT and TMV in both groups. CFT and TMV signi?cantly correlate with CS only in the TA-LF group. The r2 for CFT and CS was 0.1963 (P = 0.0206), whereas the r2 for TMV and CS was 0.3615 (P = 0.0007) at 12 weeks. No difference was observed in the incidence of CSME between the groups. Conclusion: TA-LF is associated with better CS outcomes compared to combined therapy after FLACS.
关键词： femtosecond laser-assisted cataract surgery,macular edema,liposomes,visual outcomes,contrast sensitivity
更新于2025-09-11 14:15:04
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Nanodeformation in enstatite single crystals: Simulation of micrometeoroid impacts by femtosecond pulsed laser experiments
摘要： Space weathering by micrometeoroid bombardment is a cosmic phenomenon on atmosphere-free celestial bodies, a process that is expected to particularly overprint planetesimals and cosmic dust in debris discs. We reproduced micrometeoroid impact craters by femtosecond pulsed laser irradiation on oriented enstatite single crystals (En93Fs7) to investigate the deformation behavior and its orientation dependence. All microcraters show typical bowl shaped morphologies, a glass surface layer with splash like ejecta material and subsurface layering. Although we could reproduce melting and vaporization as typical space weathering effects in the enstatite experiments, there is no formation of agglutinate particles or metallic nanoparticles (npFe0). The shock effects in the deformation layer consist of planar structures like microfractures and cleavages, amorphous lamellae, stacking faults and clinoenstatite lamellae. Their activation and/or orientation depends on the shock direction. In special orientations we observe the activation of glide systems along specific low indexed crystallographic planes. Due to the short timescale and the high strain rates, the most prominent effect is the failure of enstatite by microfracturing along non-rational crystallographic planes. Common deformation mechanisms reported in meteorites like the formation of clinoenstatite lamellae via shearing along [001] (100) occur less frequently. Shear is apparently the dominant mechanism in the formation of the above-mentioned effects and causes also their modification by frictional heating. The wide-spread formation of amorphous lamellae is, for example, interpreted to be the result of this shear heating along planar structures. We interpret this unconventional deformation behavior as a consequence of the small spatial and temporal scale of the experiments, resulting in a short-lived spherical shock wave with high deviatoric stresses in contrast to a long pressure pulse and quasi-hydrostatic compression in large scale impacts that produce typical shock features.
关键词： Femtosecond laser pulses,Space weathering,Shock deformation,Enstatite,Micrometeoroid impact
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE 10th International Conference on Mechanical and Aerospace Engineering (ICMAE) - Brussels, Belgium (2019.7.22-2019.7.25)] 2019 IEEE 10th International Conference on Mechanical and Aerospace Engineering (ICMAE) - Optical Fiber Mach-Zehnder Interferometric Strain Sensor Basedon Concatenating Two Micro Cavities Fabricated by A Femtosecond Laser
摘要： An optical fiber Mach-Zehnder interferometer (MZI) is proposed by concatenating two micro cavities that are fabricated by a femtosecond laser. The interferometer is applied for strain sensing with a sensitivity of -664.2 nm/(cid:2)(cid:2) which is comparable to long period fiber grating and taper-based strain sensors. Also, it exhibits a good reversibility in loading and unloading processes. The relationship between intensity variation and applied strain is a quadratic function. The refractive index dependence and temperature dependence of the interferometer are also investigated. Further, this structure is more robust than taper- or trench-based fiber sensors because of no reduction in fiber diameter direction.
关键词： optical fiber Mach-Zehnder interferometric,femtosecond laser,strain sensor
更新于2025-09-11 14:15:04