Femtosecond Laser Research Articles

In Vivo Femtosecond Laser Machined Transepithelial Nonlinear Optical Corneal Crosslinking Compared to Ultraviolet Corneal Crosslinking.

This study assessed the safety and efficacy of transepithelial crosslinking (CXL) using femtosecond (FS) laser-machined epithelial microchannels (MCs) followed by UVA CXL compared to FS laser (NLO CXL) in rabbits. The epithelium of 36 rabbits was machined to create 2- by 25-µm MCs at 400 MCs/mm2. Eyes were treated with 1% riboflavin (Rf) solution for 30 minutes, rinsed, and then crosslinked using UVA or NLO CXL. Rabbits were monitored by epithelial staining, optical coherence tomography (OCT) imaging, and esthesiometry. After sacrifice at 2, 4, or 8 weeks, corneas were examined for collagen autofluorescence and immunohistochemistry. NLO CXL showed no epithelial damage compared to UVA CXL, which produced on average 23.89 ± 5.6 mm2 epithelial defects that healed by day 3. UVA CXL also produced loss of corneal sensitivity averaging 0.83 ± 0.24 cm force to elicit a blink response that persisted for 28 days and remained significantly lower than control or NLO CXL. OCT imaging detected the presence of a demarcation line only following UVA CXL but not NLO CXL. Even with improved transepithelial Rf penetration, UVA CXL resulted in severe epithelial damage, loss of corneal sensitivity, and delayed wound healing persisting for a month. When MCs were paired with NLO CXL, however, these issues were mostly negated. This suggests that MC NLO CXL can achieve a faster visual recovery without postoperative pain or risk of infection. UVA CXL is a successful procedure, but there is a need for a transepithelial protocol. The combination of MCs and NLO CXL is able to keep the benefits of UVA CXL without causing epithelial damage.

Growth of high-density Zinc Oxide (ZnO) nanoflowers in all aqueous two-step method and their application in second harmonic generation of femtosecond laser

This study presents a novel two-step all aqueous solution method for the growth of high-density Zinc Oxide (ZnO) nanoflowers, utilizing ZnO powder as a precursor. For this, initially, a seed layer of ZnO nanostructures is prepared using a non-conventional sol-gel technique in an all-aqueous medium. Subsequently, high-density ZnO nanoflowers are synthesized on these seed layers through the chemical bath deposition method. Four samples, each with varying numbers of seed layers (ranging from one to four) are prepared and analyzed using field emission scanning electron microscopy (FESEM). FESEM results indicate that the sample with three seed layers exhibits optimized morphological characteristics. Consequently, further detailed investigation is conducted exclusively on this optimized sample. Furthermore, a preliminary study is done on second harmonic generation (SHG) of this optimized sample.

Ultrafast Laser Manipulation of In-Lattice Plasmonic Nanoparticles.

Plasmonic nanoparticles enable manipulation and enhancement of light fields at deep subwavelength scales, leading to structures and devices for diverse applications in optics. Despite hybrid plasmonic materials display remarkable optical properties due to interactions between components in nanoproximity, scalable production of plasmonic nanostructures within a single-crystalline matrix to achieve an ideal plasmon-crystal interface remains challenging. Here, a novel approach is presented to realize efficient manipulation of in-lattice plasmonic nanoparticles. Employing ultrafast-laser-driven plasmonic nanolithography, metallic nanoparticles with controllable morphology are precisely defined in the crystalline lattice of yttrium aluminum garnet (YAG) crystal. Through direct ion implantation, hybrid plasmonic material composed of nanoparticles embedded in a sub-surface amorphous YAG layer is created. Subsequently, femtosecond laser pulses guide formation and reshaping of plasmonic nanoparticles from the amorphous layer into the single-crystalline matrix along direction of light propagation, facilitated by a plasmon-mediated evolution of laser energy deposition. By tailoring resonance modes and optimizing the coupling between structured particle assemblies, a range of applications including polarization-dependent absorption and nonlinearity, controllable photoluminescence, and structural color generation is demonstrated. This research introduces a new approach for fabricating advanced optical materials featuring in-lattice plasmonic nanostructures, paving the way for the development of diverse functional photonic devices.

Evaluation of corneal biomechanical changes in moderate myopia after different techniques of corneal refractive surgeries

Background The most prevalent refractive error, which accounts for between 15 and 49% of cases worldwide, is myopia. Refractive surgery can fix refractive problems and lessen reliance on glasses or contact lenses. Aim This study aims to assess corneal biomechanical alterations following photorefractive keratectomy (PRK) and femtosecond laser small incision lenticule extraction (F-SMILE) in moderate myopic patients using CORVIS-ST (CST). Patients and methods This prospective, comparative, nonrandomized study was conducted on 40 patients’ eyes. with moderate myopia in a private center from January 2020 to December 2020, these eyes were subdivided into two groups: (a) The first group included 20 eyes that will receive PRK (b) The second group included 20 eyes that will receive F-SMILE. All participants will undergo operative (History taking, and examinations), preoperative (PRK, and F-SMILE), and postoperative (medications and Follow-up examinations) evaluations. Results Significant differences existed among the two groups in postoperative follow-up after 1 month and 6 months regarding deformation amplitude, radius, corvis biomechanical index, and intraocular pressure corrected biomechanically but There were insignificant differences among the two groups in terms of SPA in the same periods postoperatively. Conclusion Laser refractive surgery has a major impact on corneal biomechanical properties, as evidenced by significant changes in Corvis ST ocular biomechanical measures following PRK and F-SMILE procedures in myopic patients. The alterations resulting from F-SMILE are more substantial compared with PRK.

Phase Synchronism in the Generation of Harmonics in Gas Taking into Account Changes in the Wave Vector Detuning during the Propagation of an Intense Femtosecond Laser Pulse

Phase Synchronism in the Generation of Harmonics in Gas Taking into Account Changes in the Wave Vector Detuning during the Propagation of an Intense Femtosecond Laser Pulse

Synchronous Detection of Nonlinear Phenomena in Opto-Acoustic Vibrations Induced in a Nanofilm by a Femtosecond Laser Pulse

Synchronous Detection of Nonlinear Phenomena in Opto-Acoustic Vibrations Induced in a Nanofilm by a Femtosecond Laser Pulse

Femtosecond laser-induced plasma-assisted backward deposition of robustly adherent porous carbon films on glass substrates

The simple and rapid production and transfer of high-quality carbon materials are crucial for the flexible and efficient fabrication of carbon-based electronic devices. Recently, a laser-assisted transfer method combining laser-induced carbonization and transfer printing was demonstrated for the one-step preparation and transfer of patterned laser-induced carbon films to transparent substrates. However, this method is limited by insufficient robustness and weak adhesion of the carbon film post-transfer. Herein, we developed a non-contact laser-induced plasma-assisted deposition method to deposit robustly adherent porous carbon films on glass substrates. By well-adjusting the laser parameters and inserting spacers with adjustable thickness, laser-induced plasma ablation replaced direct laser ablation during femtosecond laser scanning of the substrate-polyimide-carrier sandwich structure, resulting in micro-channels with a carbon-glass recast layer instead of easily peelable flakes on the glass substrate. This hierarchical structure significantly enhances the adhesion between the laser-induced carbon film and the glass substrate, ensuring outstanding stability of the deposited carbon film under various adhesion tests. Furthermore, compared to carbon films prepared by the laser-assisted transfer method, the obtained carbon films are hydrophilic, low-resistance, and porous, facilitating the fabrication of energy storage devices. To demonstrate its practical application, a planar carbon-based micro-supercapacitor was fabricated on glass, exhibiting excellent electrochemical and cycling performance.

Non-destructive thickness measurement of Si wafers via optical third-harmonic generation with femtosecond laser pulses

Non-destructive thickness measurement of Si wafers via optical third-harmonic generation with femtosecond laser pulses

Nonequilibrium electronic properties and stability consequences in metallic crystalline binary alloys under ultrafast laser excitation

This study undertakes an exhaustive exploration of properties under electron-phonon nonequilibrium for a series of ten industrially pertinent crystalline alloys, namely AlCu, AlNi, AlTi, AuCu, CuNi, CuTi, NbZr, NiTi, NiZr, and ZrCu. This comprehensive investigation encompasses electronic heat capacity, electron-phonon coupling factor, excited electron density, electronic pressure, dielectric function, refractive index, extinction coefficient, reflectivity, and optical penetration depth. Employing ab initio simulations, we meticulously analyze the nonequilibrium optoelectronic attributes inherent to these alloys change under electronic excitation across the temperature range going from 0 to 50,000 K. Additionally, to contextualize the findings, we employ classical Molecular Dynamics coupled with a Two Temperature Model simulation, notably to deliver a deep comprehension of the intricate mechanisms of the CuTi alloy ablation induced by femtosecond laser irradiation.

Entrainment and multi-stability of the p53 oscillator in human cells

The tumor suppressor p53 responds to cellular stress and activates transcription programs critical for regulating cell fate. DNA damage triggers oscillations in p53 levels with a robust period. Guided by the theory of synchronization and entrainment, we developed a mathematical model and experimental system to test the ability of the p53 oscillator to entrain to external drug pulses of various periods and strengths. We found that the p53 oscillator can be locked and entrained to a wide range of entrainment modes. External periods far from p53's natural oscillations increased the heterogeneity between individual cells whereas stronger inputs reduced it. Single-cell measurements allowed deriving the phase response curves (PRCs) and multiple Arnold tongues of p53. In addition, multi-stability and non-linear behaviors were mathematically predicted and experimentally detected, including mode hopping, period doubling, and chaos. Our work revealed critical dynamical properties of the p53 oscillator and provided insights into understanding and controlling it. Arecord of this paper's transparent peer review process is included in the supplemental information.

AC Series Arc Fault Detection for Wind Power Systems Based on Phase Lock Loop With Time and Frequency Domain Analyses

AC Series Arc Fault Detection for Wind Power Systems Based on Phase Lock Loop With Time and Frequency Domain Analyses

Size Effects of Copper(I) Oxide Nanospheres on Their Morphology on Copper Thin Films under Near-Infrared Femtosecond Laser Irradiation.

The femtosecond laser direct writing of metals has gained significant attention for micro/nanostructuring. Copper (I) oxide nanospheres (NSs), a promising material for multi-photon metallization, can be reduced to copper (Cu) and sintered through near-infrared femtosecond laser pulse irradiation. In this study, we investigated the size effect of copper (I) oxide nanospheres on their morphology when coated on Cu thin films and irradiated by near-infrared femtosecond laser pulses. Three Cu2O NS inks were prepared, consisting of small (φ100 nm), large (φ200 nm), and a mixture of φ100 nm and φ200 nm NSs. A unique phenomenon was observed at low laser pulse energy: both sizes of NSs bonded as single layers when the mixed NSs were used. At higher pulse energies, the small NSs melted readily compared to the large NSs. In comparisons between the large and mixed NSs, some large NSs remained intact, suggesting that the morphology of the NSs can be controlled by varying the concentration of different-sized NSs. Considering the simulation results indicating that the electromagnetic fields between large and small NSs are nearly identical, this differential morphology is likely attributed to the differences in the heat capacity of the NSs.

The Creation of a Domain Structure Using Ultrashort Pulse NIR Laser Irradiation in the Bulk of MgO-Doped Lithium Tantalate

The fabrication of stable, tailored domain patterns in ferroelectric crystals has wide applications in optical and electronic industries. All-optical ferroelectric poling by pulse laser irradiation has been developed recently. In this work, we studied the creation of the domain structures in MgO-doped lithium tantalate by focused irradiation with a femtosecond near-infrared laser. Cherenkov-type second harmonic generation microscopy was used for domain imaging of the bulk. We have revealed the creation of enveloped domains around the induced microtracks under the action of the depolarization field. The domain growth is due to a pyroelectric field caused by a nonuniform temperature change. The domains in the bulk were revealed to have a three-ray star-shaped cross-section. It was shown that an increase in the field excess above the threshold leads to consequential changes in domain shape from a three-ray star to a triangular and a circular shape. The appearance of comb-like domains as a result of linear scanning was demonstrated. All effects were considered in terms of a kinetic approach, taking into account the domain wall motion by step generation and kink motion driven by excess of the local field over the threshold. The obtained knowledge is useful for the all-optical methods of domain engineering in ferroelectrics.

Observation of multiple topological bound states in the continuum in the photonic bilayer trimer lattice

A topological bound state in the continuum (TBIC) is a novel topological phase that has attracted significant attention. Different from conventional topological insulators (TIs), where boundary states reside within gaps, TBICs can support unconventional boundary states that remain isolated from the surrounding bulk states. In this work, we experimentally demonstrate multiple TBICs in photonic bilayer trimer lattices using femtosecond laser writing technology. By modulating the interlayer coupling between two trimer chains, we observe the emergence of two distinct types of TBICs. Moreover, we experimentally achieve the coexistence of in-gap topological states and TBICs and demonstrate the transformation between them. Our work unveils new insights into the flexible construction of TBICs, and this method can be easily applied to other one-dimensional topological structures, offering promising avenues for further research.

Generating nano/microliter droplets with on-demand repetition rates by femtosecond filament-fabricated superhydrophobic bevel needle nozzles

Nano- and micro-droplets provide a platform for microanalysis of a variety of biochemical reactions with less consumption of reagents and large-extent elimination of cross-contamination, but stable generation of such monodisperse droplets with an on-demand size and repetition rate should be first established. Here, we present a simple and robust approach to generate nano/microliter (nL/μL) droplets with predetermined size and repetition rate by using femtosecond laser filament-fabricated stainless bevel needle nozzles (BNNs). We demonstrate that hierarchically heterogeneous micro/nanostructures can be directly formed on both the inner and outer surfaces of BNNs by femtosecond laser filament processing, and that after a heat treatment the fabricated BNNs show an excellent superhydrophobic property with the water contact angle of ∼160° and the rolling-off angle of ∼0.4°. With the superhydrophobic BNNs (19–27 gauge), we produce monodisperse water droplets (2.5 μL–87 nL) with nearly the same sizes as the needle diameters, and dispense them repeatedly with on-demand repetition rates from sub-1 Hz to more than 100 Hz over several orders of the flow rate. The results provide a new way for generating microdroplets on demand for various droplet-based applications.

Controllable photoexfoliation of monolayer graphene quantum dots using temporally and spatially shaped femtosecond laser

Graphene quantum dots (GQDs) have displayed significant momentum in numerous fields due to their unique electronic properties. However, how to obtain uniformly monolayer quantum dots and explain the synthesis mechanism are still a key technical problem. Here, a rapid and controllable photoexfoliation rate of monolayer graphene quantum dots of up to 80 % was achieved by using temporally and spatially shaped femtosecond laser to ablate bulk highly oriented pyrolytic graphite targets in liquid. Theoretical calculations suggested that the temporally shaped laser can minimize the spatial range of electron excitation, maximize the Coulomb repulsion between the outer layers and Coulomb explosion within the topmost layer through multi-level electron excitation. The above multilevel photoexfoliations lead to the formation of monolayer GQDs. These findings demonstrate a perfect theoretical explanation of controllable and rapid preparation of monolayer quantum dots, accelerating its industrialization in energy storage devices.

Direct Determination of Metallic Contamination on and in Wafers Using Laser Ablation Inductively Coupled Plasma Mass Spectrometry

A new analytical technique was developed for determination of metallic impurities in wafers using LA-GED-MSAG-ICP-MS. Up to 300 mm wafer can be analyzed directly without using a small, enclosed chamber. Particles generated by a femto-second laser ablation were aspirated together with a particle free clean air by an ejector and introduced to the ICP-MS (Inductively Coupled Plasma Mass Spectrometry) via GED (Gas Exchange Device). The air was exchanged by Ar gas and the particles came out from GED in Ar gas stream. For quantitation of LA-ICP-MS, MSAG (Metal Standard Aerosol Generation) was used. MSAG could introduce nearly a 100% of aqueous multi-element standard solution to the plasma of ICP-MS, which allowed precise quantitation using the method of standard addition while ablating wafer samples. This paper describes how the new analytical technique works for ultra-trace level of metallic impurities in wafers.

Surface Coloring and Plasmonic Information Encryption at 50000 dpi Enabled by Direct Femtosecond Laser Printing.

Femtosecond (fs) laser pulses drive matter into a highly nonequilibrium state, allowing precise sculpturing of irradiated surface sites with sophisticated nanomorphologies. Here, we used fs-laser patterning to create diverse plasmonic morphologies on the top Au layer of the metal-insulator-metal sandwich. Mutual action of laser-driven thermomechanical effects and ultrafast solid-to-liquid transition allows control of the morphology resulting in pronounced surface reflectivity modulation, i.e., in a structural color effect. This enables template-free high-resolution color printing at a superior lateral resolution up to 50000 dots per inch and facile tunability of the color tone and saturation. Moreover, precise control over the orientation of the printed nanostructures within subwavelength lattices allows modulation of their local plasmonic response encrypting the optical information within the colorful images. The hidden information can be unveiled using a facile cross-polarized optical visualization scheme, rendering the proposed method with extra modalities combining high resolution information encryption, coloring, and security labeling.

O-band femtosecond mode-locked laser by using Ni-MOF in praseodymium-doped fluoride fiber

This work reports an ultrafast mode-locked fiber laser at the less investigated region of the O-band using a nickel metal-organic framework (Ni-MOF), which works as a saturable absorber (SA). Ni-MOF was prepared using the high-power laser-induced method. A stable mode-locked laser of 450 fs pulse duration was obtained. The repetition rate and signal-to-noise ratio (SNR) were 0.408 MHz and 52.5 dB, while the lasers operate at a wavelength of 1298.1 nm. At the pump power of 88 mW, the mode-locked laser was characterized to have an average output power of 0.69 mW, corresponding to a pulse energy of 1.69 nJ and a pulse peak power of 3.53 kW. Additionally, harmonic mode-locked laser operation was also achieved above the pump power of 88 mW. With the harmonic mode-locked laser operation, the pulse repetition rate increased to 2.45 MHz when the pump power was 125.7 mW. To the author's knowledge, this is the first report of novel MOF material used as an SA in praseodymium-doped fluoride fiber (PDFF) laser.

Knowledge, attitudes, and practices toward femtosecond laser small incision lenticule extraction surgery and postoperative care among recipients

BackgroundTo investigate the knowledge, attitudes, and practices (KAP) of individuals who underwent small incision lenticule extraction (SMILE) surgery and explore the influencing factors.MethodsThis cross-sectional study was conducted from June 21, 2023, to August 13, 2023, at Xiangyang Central Hospital. The participants were patients who had undergone SMILE surgery. The self-designed questionnaire had a Cronbach’s α = 0.849. Multivariable analyses were performed to determine the factors influencing the KAP scores.ResultsFinally, 485 valid questionnaires were analyzed. The median knowledge score was 14 (/17, 82.4%; IQR: 12–15). The median attitude score was 15 (/20, 75.0%; IQR: 14–16). The median practice score was 48 (/60, 80.0%; IQR: 42–54). The knowledge scores correlated to the attitude (r = 0.323, P < 0.001) and practice (r = 0.202, P < 0.001) scores, while the attitude scores correlated to the practice scores (r = 0.065, P < 0.001). College diploma (OR = 0.299, 95%CI: 0.110–0.812, P = 0.018), myopia for < 2 years (OR = 0.177, 95%CI: 0.060–0.526), and not receiving proper eye training (OR = 0.588, 95%CI: 0.402–0.862) were independently associated with knowledge. Being 19–30 years old (OR = 0.421, 95%CI: 0.235–0.756), being ≥ 31 years old (OR = 0.259, 95%CI: 0.111–0.601), myopia for 2–5 years (OR = 0.476, 95%CI: 0.232–0.978), myopia for 5–10 years (OR = 0.480, 95%CI: 0.263–0.875), and moderate myopia in the right eye (OR = 1.745, 95%CI: 1.024–2.974) were independently associated with attitude. Female gender (OR = 1.826, 95%CI: 1.196–2.787), being ≥ 31 years (OR = 2.587, 95%CI: 1.113–6.014), college diploma (OR = 3.436, 95%CI: 1.366–8.641), bachelor’s degree (OR = 2.826, 95%CI: 1.214–6.581), and not having proper eye training (OR = 0.458, 95%CI: 0.310–0.677) were independently associated with practice.ConclusionsPatients who underwent SMILE had high KAP regarding SMILE. This study identified KAP items that would warrant education.