Search Results (60)

Objectives: A Ziemer LDV Z8 femtosecond laser (FSL) was used to obtain optimal cutting parameters with precise settings for donor and recipient preparations for Bowman layer transplantation. Methods: Of 48 human research corneas examined, 32 were used for Bowman layer preparation (donor) and 16 for pocket preparation (recipient) using the LDV Z8 FSL. The cutting thickness of the Bowman layer, pocket depth, and corresponding laser settings were varied. The quality of sections was evaluated based on the occurrence of adhesions, bridges, or perforations. Histological specimens were prepared and analyzed. Results: Preparation of the Bowman layer and recipient pocket was possible using all selected settings. The thinner the Bowman layer and the more superficial the pocket preparation, the higher the risk of perforation was. Considering the fact that the Bowman layer was cut as thinly as possible, a Bowman layer thickness of 30 µm showed a 100% success rate. Bowman layers cut at 25 µm had a lower success rate (50%). The pocket depth of 150 µm showed a 100% success rate in the preparation. Histological processing revealed smooth, precisely cut edges of Bowman layers and pockets. Implantation into the pocket was successful in all cases. Conclusions: Both Bowman layer and pocket preparation were technically and surgically feasible using the LDV Z8 FSL, and the prepared Bowman layers were thinner than those reported in previous studies. The optimal Bowman layer thickness was 30 µm, and a resection depth of 150 µm was used to prepare the pockets safely. Full article

Bow-tie cavity configurations have gained significant attention due to their efficacy in facilitating stable resonator operation for applications requiring short pulse operation and high repetition rate pulses, offering versatility and reliability. While there is an extensive body of literature addressing the theoretical aspects and applications of this laser configuration, there exists a gap in practical insights and systematic approaches guidance pertaining to the development and precision alignment of this laser type. The paper achieves this by compiling a range of analytical and optimization techniques for the bow-tie cavity configuration and delineating the necessary steps for the optimization required for continuous wave operation. This ultimately leads to the attainment of the pulsed regime through the Kerr Lens Mode-locking technique, offering a detailed account of the development, optimization, and performance evaluation of a Ti:Sapphire femtosecond laser cavity, using dispersion-compensating mirrors to produce a low-energy pulse of 1 nJ, a high repetition rate of 1 GHz, and a short pulse duration of 61 fs. This work can be useful for researchers and engineers seeking to embark on the development of compact and high-performance femtosecond lasers for a spectrum of applications, encompassing biomedical imaging, laser-assisted surgery, spectroscopy, and optical frequency combs. Full article

The reflectance (R) of linear and circular micro-gratings on c-plane sapphire Al₂O₃ ablated by a femtosecond (fs) laser were spectrally characterised for thermal emission $\propto (1-R)$ in the mid-to-far infrared (IR) spectral range. An IR camera was used to determine the blackbody radiation temperature from laser-patterned regions, which showed (3–6)% larger emissivity dependent on the grating pattern. The azimuthal emission curve closely followed the Lambertian angular profile $\propto cos{\theta }_a$ at the 7.5–13 μm emission band. The back-side ablation method on transparent substrates was employed to prevent debris formation during energy deposition as it applies a forward pressure of >0.3 GPa to the debris and molten skin layer. The back-side ablation maximises energy deposition at the exit interface where the transition occurs from the high-to-low refractive index. Phononic absorption in the Reststrahlen region 20–30 μm can be tailored with the fs laser inscription of sensor structures/gratings. Full article

Background/Objectives: We report a consecutive prospective case series to obtain prospective safety and performance data of a low-energy femtosecond (FS)-laser for cataract surgery in children and to evaluate the applicability of the Bochum formula for capsulotomy diameter calculation. Methods: In pediatric lens surgery with implantation of a bag-in-the-lens intraocular lens (BIL IOL), anterior capsulotomies were performed using the FS-laser. Regression analysis was used to develop an age-dependent correction formula, and the Pearson correlation was used to evaluate the applicability of the Bochum formula. Surgery-related and ocular adverse events (AE) were recorded at 1 day, 1 week, 1 month, and 6 months postoperatively. Results: Thirteen eyes of 10 patients were included in the analysis, among them three cases of subluxated lenses. The mean age was 3.10 ± 2.38 years (range: 4 months to 8 years). The linear bivalent regression yielded the following formula: 1.27 − 0.014 × patient age. Age-related formulas, such as the Bochum formula, are required to calculate the programmed capsulotomy diameter. No complications related to the FS-laser or ocular AEs were observed up to six months; in particular, no excessive shrinkage, retinal detachment, or unusual inflammation were identified. Conclusions: This study indicates that the use of the low-energy femtosecond laser for anterior capsulotomy in pediatric lens surgery is safe and contributes to improved reliability and feasibility. The confirmed age dependence of the enlargement factor of the capsulotomy diameter might be related to the higher capsular elasticity in pediatric eyes. Full article

A method of femtosecond laser multi-pulse grid-like point etching (MP-GPE) was used to prepare glass fiber reinforced plastics with superhydrophobic properties. This article investigates the influence trend of single-pulse energy (5–35 μJ) and etching pulse number (20–100) on the morphology of surface concave holes, including depth and width. Different combinations of process parameters have a modulating effect on the size of the concave hole structure and the ablation of the reinforced plastics. At a single-pulse energy of 25 μJ and 60 pulse numbers, the depth of the concave holes increases to the maximum of approximately 63 μm, and the width of the upper surface of the concave holes is approximately 33 μm. Under these conditions, the maximum water contact angle of 160.6° is obtained, which is consistent with the theoretical calculation results of 161.6°. This is very promising for the power industry to use this material in low-temperature, drag-reducing environments. Full article

Carbon-fiber-reinforced plastic (CFRP) is a popular material possessing great properties, such as strength, lightness, and resistance to corrosion and the environment. Important steps in the production of various parts made of CFRP are surface structuring, milling, drilling and cutting processes. Here, we propose to use ultrashort pulse lasers to achieve the high-quality, low-heat-affected-zone ablation of CFRP. We investigated the ablation efficiency dependence on the processing parameters, such as the pulse duration, pulse energy and pulse overlap. We showed that good-quality results could be achieved using just low-/mid-average-power femtosecond laser equipment. We also discuss further cutting process optimization possibilities using ultrashort pulse lasers and show the possibility of HAZ-free CFRP cutting by femtosecond laser ablation. Full article

The propagation of femtosecond pulses in guided structures is a matter of both fundamental and practical interest in nonlinear optics. In particular, hollow-core waveguides (HCWs) filled with a gas medium are fabricated and used as devices for the generation of attosecond pulses from high-order harmonics. In this process, the configuration of the laser field (intensity and phase) inside the waveguide is of crucial importance for enhancing the (well-known, low) efficiency of high-order harmonic generation (HHG). Here, we present numerical calculations which demonstrate the main features of the propagation process in fabricated HCWs. We consider a variety of experimental parameters like gas pressure, waveguide size, laser wavelength, and pulse energy and duration. In particular, the beam profile at the fiber input is found to be a sensitive parameter which influences the whole evolution of the laser field along the propagation. Our model is based on a split-step method modified to account for propagation in ionized media and is validated against experimental and theoretical data from the literature. Our results contribute to the description of the main features of beam propagation in HCWs and provide guiding directions for designing efficient configurations for HHG. Full article

Graphene oxide-mediated photothermal therapy using femtosecond lasers has recently shown promise in treating hepatocellular carcinoma. However, significant work remains to optimize irradiation parameters for specific nanoparticle types and cancer cells to improve nanomaterial-mediated photothermal anticancer therapy. This study investigated the photothermal potential of nGO and nGO-PEG nanoparticles (NPs) combined with femtosecond laser irradiation at 515 nm and 1030 nm wavelengths, with varying power (0.1 and 0.2 W/cm²) and duration (5 and 10 min), to optimize photothermal therapy for hepatocellular carcinoma. Conversion efficiency of NPs, morphology and viability of HepG2 and normal MDCK cells after treatments were evaluated using an electronic thermometer, phase-contrast microscopy, and WST-1 assay. The results revealed that nGO-PEG NPs exhibited better photothermal efficiency than nGO, with 515 nm of irradiation inducing a temperature increase up to 19.1 °C compared to 4.7 °C with 1030 nm of light. Laser exposure to 515 nm significantly reduced HepG2 cell viability, with the most intense conditions (10 min at 0.2 W/cm²) causing a decrease of up to 58.2% with nGO and 43.51% with nGO-PEG. Normal MDCK cells showed minimal impact or a slight viability increase, especially with nGO-PEG. Combined treatment with laser irradiation and NPs induced significant morphological changes in HepG2 cells, including cell detachment and apoptotic-like characteristics, particularly with 1030 nm of irradiation. MDCK cells exhibited minimal morphological changes, with some recovery observed under lower energy conditions. These findings suggest that low-energy lasers and engineered nanomaterials could provide a minimally invasive approach to photothermal cancer therapy with reduced side effects. Full article

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. Full article

This article presents a comprehensive study on the impact of irradiation optical fiber cores with a femtosecond-pulsed laser, operating at a wavelength of 1030 nm, on the signal amplitude in Rayleigh scattering-based optical frequency domain reflectometry (OFDR). The experimental study involves two fibers with significantly different levels of germanium doping: the standard single-mode fiber (SMF-28) and the ultra-high numerical aperture fiber (UHNA7). The research findings reveal distinct characteristics of reflected and scattered light amplitudes as a function of pulse energy. Although different amplitude changes are observed for the examined fibers, both can yield an enhancement of amplitude. The paper further investigates the effect of fiber Bragg grating inscription on the overall amplitude of reflected light. The insights gained from this study could be beneficial for controlling the enhancement of light scattering amplitude in fibers with low or high levels of germanium doping. Full article

The dissociative ionization of CHBr₂Cl molecules in femtosecond laser fields at 800 nm and 400 nm is investigated to enhance the comprehension of ultrafast dynamics phenomena. The kinetic energy distribution of the resulting ions following photo-dissociation is analyzed using time-of-flight mass spectrometry in combination with DC-sliced ion velocity map imaging. The findings from the experimental study indicate that the presence of low kinetic energy components is attributed to the dissociative ionization processes of CHBr₂Cl molecules. The complexity of individual dissociation pathways remains unaffected by the laser fields but is determined by factors such as bond energy, ionization energy of neutral groups, and charge distribution. In the case of 400 nm laser fields, distinct elimination channels enable CHBr₂Cl⁺ ions to circumvent the transition state, leading to the formation of BrCl⁺ and Br₂⁺ fragments. Full article

High-aspect-ratio microholes, the fundamental building blocks for microfluidics, optical waveguides, and other devices, find wide applications in aerospace, biomedical, and photonics fields. Yttrium aluminum garnet (YAG) crystals are commonly used in optical devices due to their low stress, hardness, and excellent chemical stability. Therefore, finding efficient fabrication methods to produce high-quality microholes within YAG crystals is crucial. The Bessel beam, characterized by a uniform energy distribution along its axis and an ultra-long depth of focus, is highly suitable for creating high-aspect-ratio structures. In this study, an axicon lens was used to shape the spatial profile of a femtosecond laser into a Bessel beam. Experimental verification showed a significant improvement in the high aspect ratio of the microholes produced in YAG crystals using the femtosecond Bessel beam. This study investigated the effects of the power and defocus parameters of single-pulse Bessel beams on microhole morphology and size, and microhole units with a maximum aspect ratio of more than 384:1 were obtained. Based on these findings, single-pulse femtosecond Bessel processing parameters were optimized, and an array of 181 × 181 microholes in a 400 μm thick YAG crystal was created in approximately 13.5 min. The microhole array had a periodicity of 5 μm and a unit aspect ratio of 315:1, with near-circular top and subface apertures and high repeatability. Full article

Machining special microstructures on the surface of silicon nitride ceramics helps improve their service performance. However, the high brittleness and low fracture toughness of silicon nitride ceramics make it extremely difficult to machine microstructures on their surface. In this study, a femtosecond laser is used to machine parallel grooved microstructures on the surface of silicon nitride ceramics. The effects of the laser polarization angle, laser single pulse energy, scanning line spacing, and laser scan numbers on the surface morphology and geometric characteristics of grooved microstructures are researched. It is found that a greater angle between the direction of the scanning path and laser polarization is helpful to obtain a smoother surface. As the single pulse energy increases, debris and irregular surface structures will emerge. Increasing the laser scan line spacing leads to clearer and more defined parallel grooved microstructures. The groove depth increases with the increase in the scan numbers. However, when a certain number of scans is reached, the depth will not increase further. This study serves as a valuable research foundation for the femtosecond laser processing of silicon nitride ceramic materials. Full article

Purpose. This study was conducted to evaluate the effects of different capsulotomy and fragmentation energy levels on the production of oxidative free radicals following femtosecond laser-assisted cataract surgery (FLACS) with a low-energy platform. Methods. The experimental study included 60 porcine eyes (12 groups). In each group, capsulotomies with 90% or 150% energy, and fragmentations with 90%, 100%, or 150% energy or 150% with high spot density, respectively, were performed. Control samples were obtained from non-lasered eyes at the beginning (five eyes) and end (five eyes) of the experiment. In the clinical study, 104 eyes were divided into 5 groups, and they received conventional phacoemulsification (20 eyes), FLACS with 90% capsulotomy and 100% fragmentation energy levels without NSAIDs (16 eyes), FLACS with 90% (26 eyes) or 150% (22 eyes) capsulotomy energy levels, respectively, with a 100% fragmentation energy level and NSAIDs, and FLACS with 90% capsulotomy and 150% fragmentation energy levels and NSAIDs (20 eyes). Aqueous samples were analyzed for their malondialdehyde (MDA) and superoxide dismutase (SOD) levels. Results. In the experimental study, there were no significant differences in the MDA and SOD levels between the groups with different capsulotomy energy levels. An increase in the fragmentation energy from 100% to 150% led to significantly higher MDA levels in the groups with both 90% (p = 0.04) and 150% capsulotomy energy levels (p = 0.03), respectively. However, increased laser spot densities did not result in significant changes in MDA or SOD levels. In the clinical study, all four of the FLACS groups showed higher MDA levels than the conventional group. Similarly, the increase in the fragmentation energy from 100% to 150% resulted in significantly elevated levels of MDA and SOD, respectively. Conclusions. Although increasing the FSL capsulotomy energy level may not have increased free radicals, higher fragmentation energy levels increased the generation of aqueous free radicals. However, fragmentation with high spot density did not generate additional oxidative stress. Increased spot density did not generate additional oxidative stress, and this can be helpful for dense cataracts. Full article

Silicon carbide (SiC) is widely used in many research fields because of its excellent properties. The femtosecond laser has been proven to be an effective method for achieving high-quality and high-efficiency SiC micromachining. In this article, the ablation mechanism irradiated on different surfaces of 6H-SiC by a single pulse under different energies was investigated. The changes in material elements and the geometric spatial distribution of the ablation pit were analyzed using micro-Raman spectroscopy, Energy Dispersive Spectrum (EDS), and an optical microscope, respectively. Moreover, the thresholds for structural transformation and modification zones of 6H-SiC on different surfaces were calculated based on the diameter of the ablation pits created by a femtosecond laser at different single-pulse energies. Experimental results show that the transformation thresholds of the Si surface and the C surface are 5.60 J/cm² and 6.40 J/cm², corresponding to the modification thresholds of 2.26 J/cm² and 2.42 J/cm², respectively. The Raman and EDS results reveal that there are no phase transformations or material changes on different surfaces of 6H-SiC at low energy, however, decomposition and oxidation occur and then accumulate into dense new phase material under high-energy laser irradiation. We found that the distribution of structural phase transformation is uneven from the center of the spot to the edge. The content of this research reveals the internal evolution mechanism of high-quality laser processing of hard material 6H-SiC. We expect that this research will contribute to the further development of SiC-based MEMS devices. Full article