Laser Surface Ablation Research Articles

Effect of Pulsed Laser Ablation on the Increase of Adhesion of CRN Coating-Substrate

Abstract The contribution deals with analysis of the influence of the substrate surface laser ablation before deposition process to improve the adhesion of coating-substrate system. The coatings were applied to the high-speed steel 6-5-2-5 (STN 19 852) and WC-Co cemented carbide with cobalt content of 10 wt%. LAteral Rotating Cathodes (LARC®) process was chosen for evaporation of individual CrN layers. Influence of laser ablation on the substrate morphology, structure, roughness, presence of residual stresses inside the substrates and layers and their adhesion behavior between the layers and the base material was studied. Scanning electron microscopy fitted with energy dispersive spectroscopy was utilized to investigate morphology and fracture areas of substrates with CrN layers. X-ray diffraction analysis was employed to detect the residual stresses measurements. Adhesion between the coatings and substrate was analyzed using “Mercedes” testing.

Ultrasonic characterization of dry and wet nanosecond laser ablation of solids

Single-shot nanosecond laser ablation of stainless steel and copper surfaces in ambient air and liquid water environment was studied by contact broadband ultrasonics in the important laser intensity range of 6–450 GW/cm2, covering both regimes of surface phase explosion and formation of sub-critical ablative plasma via optical breakdown in the corresponding dense ablative plume. Similar dependences of ablative plasma pressure were obtained for the dry and wet ablation conditions, differing in their ultrasonic pulse amplitudes by the factor ∼5 and in their pulsewidths by the factor of 1.3 (copper) and 1.6 (steel) for the wet ablation because of the dynamic water-confinement effect. Excepting the confinement effect, these results indicate the similar conditions for pressure generation via sub-critical plasma formation both for the air and water environments, enlightening promising applications of laser ablation for liquid-assisted laser peening and generation of nanoparticles in liquids.

Safety and complications after three different surface ablation techniques with mitomycin C: a retrospective analysis of 2757 eyes.

To evaluate the safety and spectrum of complications of three excimer laser surface ablation techniques (SATs) with an intraoperative application of mitomycin C (MMC) 0.02%. A retrospective, non-comparative large case series. SATs were performed on 2757 eyes with a preoperative spherical equivalent (SE) of - 4.41 ± 2.44 and a Wavelight Allegretto 200 platform. Ablation zone diameters between 6.0 and 7.0mm were used according to mesopic pupil size. All patients were treated with an intraoperative application of MMC for 30 to 90s depending on refractive error. The mean follow-up time was > 3months (107 ± 24days). Complication range and incidence were analyzed retrospectively and safety index was calculated. Two thousand seven hundred and fifty-seven eyes met the inclusion criteria for surface ablation. Two thousand five hundred and seventy-three eyes were assigned to alcohol-assisted photorefractive keratectomy (APRK), 135 eyes to transepithelial photorefractive keratectomy (TPRK), and 49 eyes to off-flap epithelial laser in situ keratomileusis (EpiLASIK/EpiK). Overall, the safety index was 1.06 ± 0.28. Haze was graded according to the Fantes scale. Haze incidence rates were highest in the TPRK group (14.81%) and comparably low in APRK (2.95%) and EpiK (4.08%) groups. Intraoperative topical application of MMC (0.02%) results in good safety and no severe side effects. However, highest incidence of haze was observed after TPRK. The more frequent peripheral localization of haze might be attributed to large ablation zones and the wavefront optimized ablation profile especially in the PTK modus of the laser platform.

A comparative, randomized, contralateral study between the use of Mitomycin-C and accelerated cross-linking as adjuvant therapy after trans-epithelial all surface laser ablation for moderate to high myopia (ASLA-MMC vs. ASLA-XTRA): a pilot study

ABSTRACTObjectives: The purpose of our study is to compare accelerated corneal cross-linking (CXL) against topical application of Mitomycin-C (MMC), in patients undergoing all-surface laser ablation (ASLA) for moderate-to-high myopia and/or myopic astigmatism contralaterally and evaluate the efficacy of this technique in the prevention of postoperative corneal haze formation as well as the efficacy of refractive results.Methods: This prospective study consisted of 34 eyes of 17 myopic (range: −4.00 to −10.5 D, SD: 2.11) patients (8 males, 9 females). Mean age was 26.88 years (SD: 6.04, range: 19–36 years). One eye was randomly selected to ASLA with MMC while the contralateral eye underwent ASLA with accelerated CXL.Results: There was no statistically significant difference in the UDVA between the two groups at all postoperative time intervals (1,3,6, and 12 months). The keratometric values of the eyes and the haze score showed no statistically difference between the two groups at any time point.Conclusion: ASLA combined with accelerated CXL(ASLA-XTRA) appears to be a safe alternative to the use of MMC as an adjuvant treatment in moderate and high myopia. The potential additional benefits of this modality are the stabilizing effect of the refractive result and its sterilization effect on the treated cornea.

Barium ions in liquid helium

We discuss the properties of barium clusters (neutral or charged) implanted into liquid helium and propose a model where individual barium atoms cannot form negative ions, whereas a barium cluster composed of many barium atoms can. This property is important from the standpoint of applications involving laser ablation of barium metal surfaces in liquid helium. We note the qualitative differences in the mechanisms of formation of quasi-one-dimensional chains of metal or dielectric dust during its implantation into superfluid helium. A likely scenario for a dispersed metal is the dendritic breakdown in a parallel plate capacitor filled with metal dust and a finite potential difference between the plates. It is not possible to use the dendritic mechanism of cluster evolution for the dielectric problem and the details of this mechanism do not agree well with existing observations. We outline a scenario alternative to the vortex formation of long chains with dielectric links.

Designing Stainless Steel Surfaces with Anti‐Pitting Properties Applying Laser Ablation and Organofluorine Coatings

Long‐lasting and superhydrophobic stainless steel with anti‐pitting properties is achieved by modifying conventional AISI 304L through a two‐step strategy: 1) application of a femtosecond surface laser ablation treatment to generate micro‐nano structures on the surface; and 2) deposition of organofluorine nanometric coating. Samples with two different patterns, namely paraboloid‐ and cauliflower‐like, are approached and investigated by means of contact angle hysteresis, X‐ray photoelectron spectroscopy, and electrochemical techniques. Results indicate that the stainless steel surface acquires efficient anticorrosive properties due to the homogenization and refinement of the patterned microstructure into a magnetite rich phase, in combination with the formation of a carbonaceous and sol–gel layer. The adherent semiconducting oxide layer is stable over time in presence of an aggressive chloride environment. The prepared superhydrophobic surfaces prevent the steel substrates from getting wet with water, protecting them from the pitting corrosion caused by the electrolyte intrusion. The corrosion resistance is explained by a mechanism in which, in addition of the silane coating, the air trapped into the micro‐nano patterned surfaces plays an important role.

Fabrication of un-coated transparent superhydrophobic sapphire surface using laser surface ablation and heat treatment

Sapphire is a widely used hard transparent material for optics and protective windows, and a superhydrophobic coating on sapphire can prevent contamination by self-cleaning. However, the coating can be easily degraded according to time and heat. In this research, transparent superhydrophobic sapphire surfaces were fabricated via laser surface ablation, without coating, for good stability and heat resistance. The laser ablated surface showed hydrophilic initially, but the wettability transition to superhydrophobic was achieved after an additional simple heat treatment. Contact angle and transmittance were measured to confirm the superhydrophobicity and transparency, and surface analysis was performed to explain the wetting mechanism.

Surface characterization of carbon fiber reinforced polymers by picosecond laser induced breakdown spectroscopy

Adhesive bonding of composite materials requires reliable monitoring and detection of surface contaminants as part of a vigorous quality control process to assure robust and durable bonded structures. Surface treatment and effective monitoring prior to bonding are essential in order to obtain a surface which is free from contaminants that may lead to inferior bond quality. In this study, the focus is to advance the laser induced breakdown spectroscopy (LIBS) technique by using pulse energies below 100μJ (μLIBS) for the detection of low levels of silicone contaminants in carbon fiber reinforced polymer (CFRP) composites. Various CFRP surface conditions were investigated by LIBS using ∼10ps, 355nm laser pulses with pulse energies below 30μJ. Time-resolved analysis was conducted to optimize the gate delay and gate width for the detection of the C I emission line at 247.9nm to monitor the epoxy resin matrix of CFRP composites and the Si I emission line at 288.2nm for detection of silicone contaminants in CFRP. To study the surface sensitivity to silicone contamination, CFRP surfaces were coated with polydimethylsiloxane (PDMS), the active ingredient in many mold release agents. The presence of PDMS was studied by inspecting the Si I emission lines at 251.6nm and 288.2nm. The measured PDMS areal densities ranged from 0.15 to 2μg/cm2. LIBS measurements were performed before and after laser surface ablation. The results demonstrate the successful detection of PDMS thin layers on CFRP using picosecond μLIBS.

Long-Term Results of Excimer Laser Surface Ablation with Smoothing for High Myopia

Purpose: To evaluate long-term refractive, aberrometric and anatomical results of surface ablation plus corneal PTK-style smoothing for myopia greater than –7.00 D. Methods: One-hundred-and-fourteen eyes of 69 patients (mean age: 37.7 ± 8.3 years) underwent PRK with the NIDEK EC-5000 excimer laser (NIDEK Co. Ltd., Gamagori, Japan) using multiple optical zones ranging in diameter from 4.89 mm to 7.0 mm, and transition zones (TZ) that were at least 3 mm wider than the optical zones (OZ). A cross-cylinder technique was used for treating astigmatism greater than 0.50 D. All eyes underwent a phototherapeutic keratectomy (PTK) smoothing technique using masking fluid. The Student’s t-test was used to determine a statistically significant change after surgery. A p value less than 0.05 was considered statistically significant. Results: Preoperative corrected distance visual acuity (CDVA) was 0.88 ± 0.16 with –9.53 ± 1.18 D cycloplegic spherical equivalent (SE). Preoperative corneal pachymetry was 560.4 ± 30.1 µ. Three years after surgery uncorrected visual acuity (UCVA) was 0.79 ± 0.26, CDVA was 0.92 ± 0.19 with –0.56 ± 0.90 D SE. Mean corneal haze was highest 1 month after surgery (0.58 ± 0.35), then progressively decreased to 0.11 ± 0.32 by 3 months postoperatively. Following year one, refraction and corneal curvature remained stable. There were no cases of keractasia to date. There was no hyperopic induction due to PTK. Two eyes required retreatment due to undercorrection. Total wavefront error did not change significantly, while astigmatism decreased and coma increased (both with p< 0.001). Conclusion: Surface ablation for the treatment of high myopia using PTK smoothing with a masking fluid was safe and effective. Wide optical and transition zones prevented induction of spherical aberration and the incorporation of the smoothing technique created a regular corneal surface with regular healing and trace to no haze after surgery.

Epi-Bowman-Keratektomie: klinische Beurteilung einer neuen Variante der Surface Ablation

A new device for epithelial abrasion before excimer laser surface ablation or corneal cross-linking (CXL) has recently been introduced (Epi-Clear™, Orca Surgical, Kiryat-Shmona, Israel). We have reviewed the literature on the clinical results, potential benefits and drawbacks of this instrument, compared to other methods of epithelial removal. Literature search for "Epi-Bowman Keratectomy", "Epi-clear", and "Epikeratome" yielded 1 peer-review publication, 1 non-peer-review publication, 18 posters and presentations at international conferences (European Society of Cataract and Refractive Surgeons [ESCRS] and American Society of Cataract and Refractive Surgery [ASCRS]) on the use of the Epi-Clear™ device before surface ablation, 2 posters on the use of Epi-Clear before corneal crosslinking and 1 presentation on the experimental use of Epi-Clear for removal of a pterygium. Comparison of laser ablation after epithelial removal with the Epi-Clear device (Epi-Bowman Keratectomy™, EBK™) to other established methods of surface ablation, i.e. alcohol-assisted PRK or PRK with a metallic scraper, EBK, suggests that the results are generally similar. Pain perception, haze formation, and epithelial healing are reported to be better than with conventional surface ablation methods. Studies evaluating the use of the Epi-Clear device before CXL report that the healing time is significantly reduced and that less pain is perceived. The Epi-Clear device seems to be a promising new option for epithelial removal before refractive laser ablation, although a convincing explanation for its potential superiority is still missing. In contrast, when the Epi-Clear device is used before CXL, then the Bowman's layer remains intact; this may provide an adequate explanation for the reported benefits of this application. However, currently available studies are of low level of evidence, so that more prospective randomised trials are needed for a robust evaluation of this treatment.

Reduction of secondary electron yield for E-cloud mitigation by laser ablation surface engineering

Developing a surface with low Secondary Electron Yield (SEY) is one of the main ways of mitigating electron cloud and beam-induced electron multipacting in high-energy charged particle accelerators. In our previous publications, a low SEY<0.9 for as-received metal surfaces modified by a nanosecond pulsed laser was reported. In this paper, the SEY of laser-treated blackened copper has been investigated as a function of different laser irradiation parameters. We explore and study the influence of micro- and nano-structures induced by laser surface treatment in air of copper samples as a function of various laser irradiation parameters such as peak power, laser wavelength (λ=355nm and 1064nm), number of pulses per point (scan speed and repetition rate) and fluence, on the SEY. The surface chemical composition was determined by x-ray photoelectron spectroscopy (XPS) which revealed that heating resulted in diffusion of oxygen into the bulk and induced the transformation of CuO to sub-stoichiometric oxide. The surface topography was examined with high resolution scanning electron microscopy (HRSEM) which showed that the laser-treated surfaces are dominated by microstructure grooves and nanostructure features.

A study on curved surface laser ablation using beam profile approach

Laser ablation process was used to generate micro-scale curved surfaces that find applications such as micro-lens and hydrophobic surfaces. Curved surface laser ablation to produce micro-scale features generally involves altering the spatial beam profiles using masks with varying spatial opacity. The surface profile obtained mainly depends on the altered laser beam profile. This work aimed at understanding the influence of laser beam profile on the generated surface in curved surface laser ablation. The study was based on a 2D finite element model of laser ablation that considered target heating, heat transfer and vaporisation on a poly methyl methacrylate (PMMA) target. Using this model, surface profile was predicted for various profiles of laser intensity and a qualitative analysis of curved surface profiles was carried out. The quantitative comparison of the ablation depths for uniform beam was used to validate the numerical model. The results of ablation depth were found to be in good agreement with that of the experiments.

A study on curved surface laser ablation using beam profile approach

A study on curved surface laser ablation using beam profile approach

Mitomycin C for prevention of postoperative haze following excimer laser surface ablation in moderate to high myopia

Reason for withdrawal from publication The protocol is out of date and does not meet the current methodological standards of Cochrane.

Assessment of Tablet Surface Hardness by Laser Ablation and Its Correlation With the Erosion Tendency of Core Tablets

Surface erosion of uncoated tablets results in processing problems such as dusting and defects during coating and is governed by the strength of particle bonding on tablet surface. In this study, the correlation between dusting tendency of tablets in a coating pan with friability and laser ablation surface hardness was assessed using tablets containing different concentrations of magnesium stearate and tartaric acid. Surface erosion propensity of different batches was evaluated by assessing their dusting tendency in the coating pan. In addition, all tablets were analyzed for crushing strength, friability, modified friability test using baffles in the friability apparatus, and weight loss after laser ablation. Tablets with similar crushing strength showed differences in their surface erosion and dusting tendency when rotated in a coating pan. These differences did not correlate well with tablet crushing strength or friability but did show reasonably good correlation with mass loss after laser ablation. These results suggest that tablet surface mass loss by laser ablation can be used as a minipiloting (small-scale) tool to assess tablet surface properties during early stages of drug product development to assess the risk of potential large-scale manufacturing issues.

Progress in the Design of New Photonics and Optoelectronics Elements Using Advantages of Contemporary Femto-Nanophotonics

We consider experimentally and theoretically the detection of quantum states in nanocluster semiconductor/metal structures upon the registration of hopping/tunneling electrical conductivity and possible mechanisms of realization of such states. We obtain nanostructured thin films on the substrates using different technologies, including laser ablation of solid surfaces. We show that it is possible to control the properties of the films by varying the topology of such synthesized systems. We analyze the features arising due to the specific conductivity of granular media revealed by the measured current–voltage characteristics and electrical resistance dependences for nanocluster bimetallic films of different compositions.

Effect of laser ablation surface treatment on performance of adhesive-bonded aluminum alloys

Abstract This study was conducted to investigate the effect of laser ablation surface treatment on the joint performance of AA6022-T4 2.0 mm adhesively bonded to itself. It was found that laser ablation treatment at higher energy fluence (i.e., 19.01 J/cm 2 ) improved the joint strength by 25% versus untreated material as measured after water soak exposure. Furthermore, a greater proportion of fracture surface exhibited pure cohesive failure following laser ablation treatment. Results revealed that while laser ablation treatment at lower energy fluence had little influence on the surface topography (though it did act to remove any sheet metal lubricant or other contaminants), treatment at higher energy fluence increased both surface roughness and surface area. This is considered a contributing factor to the improved adhesive bond performance. However, the higher energy fluence were also found to modify the surface chemistry and created a more uniform and thicker aluminum oxide layer, which was likely to be another contributing factor to the improved bond performance. Additionally, the effect of aging (up to 6 weeks) in ambient conditions of laser ablated aluminum on adhesive bonding performance appeared to have no statistical influence.

Long-Term Clinical Outcomes of Myopic Patients Having Thin Residual Corneal Thickness after Excimer Laser Surface Ablation

ABSTRACTPurpose: To investigate and compare the long-term safety, efficacy, and accuracy of PRK (photorefractive keratectomy) and LASEK (laser epithelial keratomileusis) in myopic corneas having residual corneal thickness less than 400 micron meters (µm). Methods: The medical reports of the patients who had undergone excimer laser surface ablation between 2007–2011 and had a residual corneal thickness less than 400 µm were retrospectively reviewed. Results: Forty-two eyes of 42 patients with a mean age of 28.79±7.76 years were enrolled into the study. Twenty-two PRK and 20 LASEK procedures were performed. The mean follow-up time was 45.00±11.80 months. At the end of follow-up, no ectasia was detected. Nineteen percent of eyes had trace haze. No eyes lost any lines in corrected distance visual acuity. Eighty-one percent of the patients had an uncorrected distance visual acuity better than 20/40. The regression rate was 16.7%. Sixty-two percent of eyes were within ±1.00 D. The safety and efficacy indexes were 1.19±0.42 and 1.00±0.40, respectively. There was not any difference between LASEK and PRK regarding achieved spherical equivalent refraction, haze ratio, visual acuity, safety, efficacy, and regression. Conclusions: Both PRK and LASEK are safe and effective in myopic corneas having thin residual thickness.

Ultrafast electron dynamics of material surfaces under the action of femtosecond laser pulses

Electric collector investigations of the singleand multi-shot femtosecond laser ablation of optical-quality surfaces of different materials, including aluminum, copper, titanium, silicon, and graphite, show that the emission of erosion plasma is significantly lower than the energy density of laser ablation of these materials and replaces the dominant electron emission at lower energy densities. I–V characteristics and cumulative dependences of the collector signal are studied in the emission mode. The observed dependences of the electron and plasma emission signals on the laser pulse energy density are discussed.

Nonlinear absorption mechanisms during femtosecond laser surface ablation of silica glass

Spatial profiles of single-shot microcraters produced by tightly focused femtosecond laser pulses with variable pulse energies are measured by means of a laser confocal microscope. Dependences of crater depth on laser intensity at different pulse energies appear as overlapping saturating curves with the same threshold, indicating the presence of nonlinear absorption and absence of nonlocal ablation effects. A monotonic twofold increase in absorption nonlinearity is related to the transition from minor defect-band absorption to fundamental band-to-band absorption.