Pulsed Laser Treatment Research Articles

Laser heat treatment effect on fatigue of hinged cantilever beams

The paper considers the effect of laser hardening treatment of steels on the fatigue strength of materials. The statement of efficiency of laser processing for formation of hard surface layer of processed surface which protects from wear is substantiated in relation to a hinge design in agricultural machines placed on a cantilever fastened beam which is a hinge axis. The phenomenon of reduction of fatigue characteristics of structural steels after laser treatment is investigated. Influence of fatigue loading on beam durability is analyzed. On the basis of experimental data analysis, the conclusion is formulated that the surface defects in the form of wells which are formed under the influence of laser pulse play an important role during the pulse laser treatment. Particular attention is paid to the role of residual stresses generated by the thermal effects of the laser. On the basis of this research, it is recommended that laser hardening treatment should be carried out, the pulse energy of which does not lead to surface melting.

Effect of pulse laser treatment at different process variables on mechanical behavior of carbon nanotubes electrophoretically deposited on titanium alloy

Purpose Titanium and its alloys are widely used as biomaterials for long-term implants, but they are usually surface-modified due to their weak bioactivity and wear resistance. Laser processing was used to modify the surface layer, and elemental carbon was a component of the deposited coatings. This research aims to use a combination of both methods based on preliminary electrophoretic deposition of multi-wall carbon nanotubes (MWNCTs) followed by pulse laser treatment. Carbon nanotubes were chosen due to their mechanical and chemical stability as well as their tubular shape, resulting in enhanced mechanical properties of laser-modified layers. Methods The pulse laser power and laser scanning speed were defined as variable process parameters. The microstructure, roughness Ra, nanohardness H, Young`s modulus E, and indent depth values were measured, and the H/E, H3/E2, and relative changes of all these values in comparison to MWCNTs-coated and non-coated surfaces, were calculated. Results The obtained results show that the best mechanical properties of MWCNTs-coated and laser-treated specimens are obtained at a laser power of 900 W and laser feed of 6 mm/s. The observed relations can be explained considering processes occurring on the surface such as deposition of carbon nanotubes, melting and re-crystallization of the surface layer, formation and possible partial decomposition of titanium carbides, and associated changes in local chemical composition, phase composition, and a level of residual stresses beneath the surface. Conclusions The developed process can substitute the time and money-consuming carbonization of titanium and its alloys.

Influence of Surface Modification of Titanium and Its Alloys for Medical Implants on Their Corrosion Behavior.

Titanium and its alloys are often used for long-term implants after their surface treatment. Such surface modification is usually performed to improve biological properties but seldom to increase corrosion resistance. This paper presents research results performed on such metallic materials modified by a variety of techniques: direct voltage anodic oxidation in the presence of fluorides, micro-arc oxidation (MAO), pulse laser treatment, deposition of chitosan, biodegradable Eudragit 100 and poly(4-vinylpyridine (P4VP), carbon nanotubes, nanoparticles of TiO2, and chitosan with Pt (nano Pt) and polymeric dispersant. The open circuit potential, corrosion current density, and potential values were determined by potentiodynamic technique, and microstructures of the surface layers and coatings were characterized by scanning electron microscopy. The results show that despite the applied modifications, the corrosion current density still appears in the region of very low values of some nA/cm2. However, almost all surface modifications, designed principally for the improvement of biological properties, negatively influence corrosion resistance. The reasons for observed effects can vary, such as imperfections and permeability of some coatings or accelerated degradation of biodegradable deposits in simulated body fluids during electrochemical testing. Despite that, all coatings can be accepted for biological applications, and such corrosion testing results are presumed not to be of major importance for their applications in medicine.

Recurrence of premalignant oral cavity and oropharynx lesions after pulsed diode laser treatment

PurposeLeukoplakia is common with a 1 % incidence in the population and may harbor preneoplastic changes. Diode lasers provide both precision and coagulation for excision of superficial lesions in clinical and operative settings with little damage to deeper tissue. We aim to determine the rate of oral and oropharyngeal hyperkeratosis and dysplasia recurrence after treatment with diode laser. Materials and methodsPatients with oral or oropharyngeal hyperkeratotic or mild dysplastic lesions treated with pulsed diode laser between 2013 and 2020 at a tertiary academic institution were analyzed. The main outcome measure was recurrence of hyperkeratosis and dysplasia after treatment. ResultsFourteen patients received diode laser treatment for hyperkeratotic or mild dysplastic lesions of the oral cavity or oropharynx. Demographic features included 9 (64.3 %) females and mean age of 66.6 years. In these 14 patients, 18 distinct lesions were identified. Eleven (61.1 %) lesions were located on the oral tongue, 4 (22.2 %) on the buccal mucosa, 2 (11.1 %) on the hard palate, and 1 (5.6 %) on the soft palate. Average time from lesion clinical diagnosis to the first diode laser treatment was 8.3 months with an average number of 1.4 treatments per lesion. Three (16.7 %) lesions experienced recurrence after the most recent treatment. None of the lesions underwent malignant transformation. None of the patients experienced bleeding, tethering, or dysarthria after treatment. One patient developed pyogenic granuloma and reported chronic tongue pain. ConclusionsPulsed diode laser treatment of leukoplakia was well tolerated with low complication rates and reasonable control of precancerous lesions.

248 Functional and psychological outcomes of combined pulsed dye laser and fractional carbon dioxide laser treatment for scars in pediatric patients

Scars can manifest with cosmetic disfigurement, functional impairment, and discomfort which can be particularly impactful in children and adolescents. Laser therapy has been recently developed as a useful modality to improve both the appearance of scars and the functional status of patients. Our study aims to determine an association between ratings of blind evaluators and patient reported outcomes in pediatric scar patients pre- and post-treatment with combined pulsed dye laser (PDL) and fractional carbon dioxide (CO2) laser therapy.

Influence of a Laser Irradiation and Laser Scribing on Magnetic Properties of GO Silicon Steels Sheets Using a Nanosecond Fiber Laser

Improving the performance of electrical steels within the magnetic circuits is essential to save energy. The domain refinement through local surface treatment by laser is an effective technique to reduce the iron losses in grain-oriented iron silicon steels. To interpret the mechanism of this technique, we have quantitatively studied the impact of nanosecond pulse laser treatment on the magnetic properties of grain-oriented Fe(3%wt)Si sheets. We measured the total power loss and apparent permeability of the samples using a Single-Sheet Tester (SST). The laser treatment resulted in a loss reduction of up to 24% compared to the average power loss of standard samples at 50 Hz. At mid-induction levels, the reduction was also accompanied by an improvement in apparent permeability. A dynamic magnetic behavior law was used to identify a dynamic property Λ including information on density, surface area and wall mobility and another internal permeability property µ representative of static field and magnetization characteristics. Lastly, we presented the behavior of these properties under different laser treatment.

Nanosecond, picosecond and femtosecond laser surface treatment of magnesium alloy: role of pulse length

Despite having a whole range of applications as in weight-saving structures, biodegradable implants and rechargeable batteries, the usage of magnesium is still hindered by its high tendency to corrosion. Pulsed laser treatments are an interesting approach to modify the surface of magnesium aiming the improvement of the corrosion properties as well as the generation a controlled roughness, which is useful for improving coatings adhesion or tailoring the interactions with living cells at the surface of an implant. In this work, a novel study on the role of the pulse length on topography and corrosion properties of AZ31 magnesium alloy laser-treated surfaces is presented. Three different laser sources with pulse lengths of 20 ns, 800 ps and 266 fs were employed with a similar experimental setup. Surface topography analysis revealed a reduction of the amount of melt generated and an increase in the aspect ratio (depth/width) of the ablated features as the pulse length is reduced. All three treatments significantly improved the corrosion performance of the untreated base material. Thicker and more homogenously distributed recast material for the longer pulses of the nanosecond treatment resulted in a longer-lasting protection (11–12 fold reduction in mass loss rate vs base material) compared to the pico- and femtosecond treatments (4–5 fold reduction). • The role of pulse length in laser treatments of AZ31 magnesium alloy is studied. • Nanosecond, picosecond and femtosecond laser surface treatments are compared. • Shorter pulse length reduces the molten material and sharpens topography features. • Corrosion of untreated material is drastically reduced with the laser treatments. • Longer pulse length provides a longer-lasting corrosion protection.

The influence of Nd: YAG pulsed laser treatment on the structure, morphology and hardness of e.max ceram dental material

The use of ceramics in dentistry is increasing day by day owing to their more aesthetic look, better mechanical properties, and easy-to-fit approach. The material used in the study is IPS e.max Ceram by Ivoclar Vivadent which has been widely adopted as the ceramic of choice by many dentists as it is ideally suitable for the veneering of more opaque substructures. The study aims to elucidate the result of Nd: YAG pulsed laser irradiation at different numbers of pulses on structure, surface morphology, and hardness of e.max Ceram dental material. XRD shows the amorphous nature of the material before the laser irradiation, whereas the crystallinity in the material is slightly induced after the exposure of e.max Ceram with 150 laser shots. The surface morphology and hardness degradation are attributed to the swelling potential of the material and induced increase of the residual micro-stresses during laser irradiation. This technique could provide more ease for bonding and de-bonding of orthodontic brackets and might be used as a chairside tool.

Preparation of silicon and aluminum nanoparticles in an aqueous solution

The interest in nanomaterials is due to a significant change in their physical properties compared to massive materials. Changes in the physical and chemical properties of particles containing several hundred or thousands of atoms are determined by changes in the density of electronic states.Aqueous solutions of aluminum and silicon nanoparticles were obtained by laser ablation. Pulsed laser treatment was performed in the mode of double pulses in distilled water. The invested energy was: for aluminum 1000–1500 J, the exposure time is 10–25 min., for silicon-50–1000 J with exposure times from 1 to 10 min.The features of the morphology of the obtained particles, as well as the surface of polycrystalline aluminum and silicon craters, were determined by scanning electron microscopy. It is shown that an ensemble of particles of different sizes from 20 nm to 2.0 microns is formed. Some aluminum particles are cut, which allows us to talk about their cristallinity. It is shown that the structure of the target surface after laser exposure consists of grains separated from each other by thermal etching grooves, since the evaporation of the material occurs primarily along the grain boundaries.

Effect of CO2 laser treatment on the leather surface morphology and wettability

The aim of this research was to determine the influence of pulsed CO2 laser treatment on crust leather surface morphology and wettability. The obtained results revealed that pulsed CO2 laser engraving can be used as an effective tool for crust leather surface treatment. Pulsed CO2 laser treatment only negligible affects the macrostructure of leather, while the morphology and wetting of the leather surface after treatment were changed. It was found that an increase of laser pulses number increases the initial water contact angle value and intensifies the water droplet relaxation process. After laser treatment, the water droplet contact angle relaxation rate increases twofold compare to those for untreated leather. SEM micrographs showed increased defectiveness with rough surface patterns, thermally affected areas, and change of microstructure. The EDX analysis revealed that the engraved leather surface contains a significantly higher amount of carbon but smaller quantities of oxygen compared to those of untreated samples. It was found that only after laser treatment chromium and sulfur in the EDX spectra appear while for untreated samples these elements on the surface were not observed. The results indicate that for investigated samples laser engraving does not affect the concentration of hexavalent chromium and are in accordance with EU requirements.

Pulse laser processing of hard-alloy cutting tool with multilayer coating

The influence of pulsed laser treatment (PLT) on the structural parameters and mechanical properties of singlelayer and multilayer coatings is investigated. The contact indicators during cutting, indicators of the thermal and stressed state of the cutting wedge of a tool with multilayer coatings that have passed the PLT are presented. The effectiveness of PLT for multi-coated carbide cutting tool is shown. Keywords: pulsed laser processing, carbide cutting tool, multilayer coating, structural indicators, indicators of mechanical properties, durability period. vpt1947@yandex.ru, serg.sizov24@yandex.ru

Influence of Retinal Microsecond Pulse Laser Treatment in Central Serous Chorioretinopathy: A Short-Term Optical Coherence Tomography Angiography Study.

Background: Central serous chorioretinopathy (CSC) is a common macular condition characterized by detachment of the neuroretina and is a frequent cause of central vision loss in adults. Among the various therapeutic strategies, subthreshold microsecond pulsed laser (SML) treatment has become a useful option. Despite the suggested involvement of choroidal circulatory disturbances in CSC, the effects of this treatment on macular microperfusion have not been fully evaluated yet. Herein, we report the impact of SML on retinal and choroidal microvascular flow using non-invasive optical coherence tomography (OCT) angiography (OCTA). Methods: In this study, CSC patients with persistent subretinal fluid (SRF) with or without secondary choroidal neovascularization (CNV) were included (referred to as the pachychoroid neovasculopathy (PNV) group and the CSC group, respectively). SML was conducted using a yellow (577 nm) laser with a duty cycle of 10%, spot size of 200 µm and duration of 200 ms. Best corrected visual acuity (BCVA) as well as OCT and OCTA images were evaluated at baseline and 4 weeks after SML. OCTA parameters of interest included full retinal perfusion (FRP), choriocapillaris perfusion (CCP), Sattler’s layer perfusion (SLP), and Haller’s layer perfusion (HLP), which were evaluated longitudinally and compared to unaffected fellow eyes. Results: 27 affected eyes and 17 fellow eyes from 27 patients were included. Before treatment, central retinal thickness (CRT) and subfoveal choroidal thickness (SFCT) of affected eyes were significantly larger than in fellow eyes. Four weeks after SML, CRT decreased significantly, whereas perfusion parameters did not change. In subgroup analyses, the CSC group showed a significant decrease in SFCT, whereas the PNV group did not despite the decrease in CRT. Conclusion: Our results suggest that the SML may affect the SFCT of the CSC, but not the PNV patients at least within four weeks following treatment. This effect seems to be independent of the change in choroidal perfusion measured with OCTA.

Quasi long-pulsed 1064nm Nd:YAG (micro pulsed) technology for the treatment of active acne: A case series.

Acne vulgaris is common dermatologic condition with an estimated prevalence of 80%. Acne has been shown to have a significant impact on patient quality of life and mental health, especially as inflammatory lesions typically occur on cosmetically sensitive areas with the potential for permanent scarring. There have been numerous advances in the treatment of inflammatory acne with light-based and laser devices. This technology permits effective treatment of active acne and scarring, with a short recovery and a decreased side effect profile as compared to medicinal standard-of-care and photodynamic therapies. The case series study was aimed at evaluating the safety and efficacy of a 1064nm Nd: YAG Quasi-longed pulse laser treatment for acne vulgaris. This was a prospective study of 19 subjects with moderate to severe. All subjects received 1064nm Nd: YAG Quasi-longed pulse laser treatments, at 8J/cm2 fluence and accumulated 1000-4000kJ according to treatment area at two weeks intervals. Primary end point was reaching a minimal AGSS score of between 1 and 2. Acne severity was assessed by two independent dermatologists according to AGSS scale before each treatment session and at the follow-up visit (8weeks following last treatment). Subjects' self-assessment of Patient Global Impression of Change (PGIC) and overall satisfaction were also recorded. Safety was assessed by recording pain, adverse events, and downtime throughout the trial. Investigator's US FDA AGSS scoring of acne appearance improvement shows an average of 6.6 treatments were required to reach the minimal AGSS score endpoint. Significant reduction in AGSS scores was recorded after 2 treatments (4.21±0.65 vs 3.05±0.83 p=1.63E-05 ), and maintained a statistically significant reduction rate throughout the trial. Minimal AGSS scores were still detected after 8weeks following final treatment. Subjects scored high satisfaction rates and PGIC scores (2.9 and 5.3, respectively). Some patients reported transient erythema as only adverse events recorded in the study. The 1064nm Nd: YAG Quasi-longed pulse laser was found to be safe and highly effective for the treatment of facial acne. The treatments were well tolerated, and the subjects experienced no pain and no downtime. Light-based treatments do and will probably continue to play an important and enlarging role in acne management.

Effect of laser treatment on the characteristics of martensitic transformation in Fe–Ni alloy

The effect of pulsed laser treatment on the structural state and internal stresses of the Fe–Ni alloy has been studied. The influence of the size of austenitic grains, redistribution of chemical elements and internal stresses in the austenitic phase on the characteristics of martensitic transformation in the subsurface layer of the alloy was analyzed. A correlation between the grain size effect of martensitic transformation and the amount of martensitic phase in this layer was established.

A wavelet approach for the variable-order fractional model of ultra-short pulsed laser therapy

In this paper, the ultra-short pulsed laser treatment is numerically simulated for a focused laser beam applied to a cylindrical domain. To do so, the general form of the variable-order fractional-order, dual-phase lag bioheat transfer equation is implemented. To determine the major affecting parameters, the dimensionless form of the heat equation is derived and solved numerically. An efficient method based on the 2D Legendre wavelets is developed to provide a numerical solution for this variable-order time fractional model. The man advantage of the proposed algorithm is that it converts the solution of the problem into solution of a system of algebraic equations. The validity of the formulated method is investigated through one numerical example. The effect of several operational and thermo-physical properties including the phase lag time, fractional order, and the duration of active laser beam in each on/off cycle on the thermal field and heat penetration depth is examined. According to the results, it is concluded that by increasing the fractional order from 0.1 to 0.9, 65.1% increase in the penetration length occurs.

INFLUENCE OF FEMTOSECOND LASER PROCESSING PARAMETERS ON THE SURFACE MORPHOLOGY AND WETTABILITY PROPERTIES OF POLYLACTIC ACID

Polylactic acid (PLA) is a very attractive material for applications in the field of regenerative medicine and tissue engineering, as it is a biocompatible and biodegradable synthetic polymer, whose morphological properties can be finely tuned via laser processing. Ultra-short pulse laser treatment is a non-invasive method for optimizing the surface properties of engineered biomatrices. The method offers controlled porosity of the treated biomaterial tailored specifically for implantation needs. In this research, we investigated the interaction of femtosecond laser radiation with PLA stacks while varying the output laser parameters in order to estimate their influence on the morphology of the PLA samples. The induced microstructural features were characterized by thickness measurements and SEM, EDX and FTIR analyses. In order to evaluate the hydrophilicity of the treated surface, water contact angle (WCA), measurements were also performed. Topography modification of the PLA substrates could essentially improve this material’s bioactivity properties, which, after proper optimization of the laser parameters, could make its biomedical applications even more successful.

Effects of combined Pulsed Dye Laser and Fractional CO2 Laser treatment of burn scars and correlation with plasma levels of collagen type I, MMP-2 and TIMP-1

Hypertrophic burn scars remain a significant burden for patients and a challenge for clinicians. The aimAssessement of the efficacy of combined Pulsed Dye Laser and Ablative Fractional CO2 Laser therapy on hyperthophic scars and correlation with plasma levels of MMP-2, TIMP-1 and alpha-1 type I collagen. Patients and methodsTwenty five pediatric subjects were enrolled into the study. Control group consisted of age-matched subjects admitted for surgical repair of inguinal hernia. For the assessment of the results of laser treatment we used the Vancouver scar scale (VSS), and Patient-Observer Scar Assessment Scale (POSAS). We also correlated clinical results with plasma levels of MMP-2, TIMP-1 and alpha-1 type I collagen. ResultsAll subjects reported the laser treatment resulted in improvement and were somewhat satisfied or very satisfied with their experience. No adverse events were reported. The levels of MMP-2, TIMP-1 and alpha-1 type I collagen in our patients with scars before laser threatment were higher in comparison to controls. We also found statistically significant decrease in the levels of MMP-2, TIMP-1 and alpha-1 type I collagen after laser treatment of burn scars ConclusionsOur study clearly shows that combined CO2-AFL treatment for burn scars improve texture, colour, function and alleviate pruritus. We believe that decrease in the levels of MMP-2, TIMP-1 and alpha-1 type I collagen after laser treatment of burn scars, reflects reduced dynamic of scar.

Formation of the hollow nanopillar arrays through the laser-induced transformation of TiO2 nanotubes

In the following article, we present a simple, two-step method of creating spaced, hollow nanopillars, from the titania nanotube arrays via pulsed laser-treatment. Due to the high ordering of the structure, the prepared material exhibits photonic properties, which has been shown to increase the overall photoefficiency. The optical and morphological changes in the titania nanotubes after pulsed laser-treatment with 532, 355, and 266 nm wavelengths in the 10–50 mJ/cm2 fluence range are studied. The investigation reveals, that by using appropriate wavelength and energy, the number of surface defects, geometrical features, or both can be tailored.

The Effect of Laser Re-Solidification on Microstructure and Photo-Electrochemical Properties of Fe-Decorated TiO2 Nanotubes.

Fossil fuels became increasingly unpleasant energy source due to their negative impact on the environment; thus, attractiveness of renewable, and especially solar energy, is growing worldwide. Among others, the research is focused on smart combination of simple compounds towards formation of the photoactive materials. Following that, our work concerns the optimized manipulation of laser light coupled with the iron sputtering to transform titania that is mostly UV-active, as well as exhibiting poor oxygen evolution reaction to the material responding to solar light, and that can be further used in water splitting process. The preparation route of the material was based on anodization providing well organized system of nanotubes, while magnetron sputtering ensures formation of thin iron films. The last step covering pulsed laser treatment of 355 nm wavelength significantly changes the material morphology and structure, inducing partial melting and formation of oxygen vacancies in the elementary cell. Depending on the applied fluence, anatase, rutile, and hematite phases were recognized in the final product. The formation of a re-solidified layer on the surface of the nanotubes, in which thickness depends on the laser fluence, was shown by microstructure studies. Although a drastic decrement of light absorption was recorded especially in UV range, laser-annealed samples have shown activity under visible light even 20 times higher than bare titania. Electrochemical analysis has shown that the improvement of photoresponse originates mainly from over an order of magnitude higher charge carrier density as revealed by Mott-Schottky analysis. The results show that intense laser light can modulate the semiconductor properties significantly and can be considered as a promising tool towards activation of initially inactive material for the visible light harvesting.

Rational collaborative ablation of bacterial biofilms ignited by physical cavitation and concurrent deep antibiotic release

Bacteria biofilm has extracellular polymeric substances to protect bacteria from external threats, which is a stubborn problem for human health. Herein, a kind of gasifiable nanodroplet is fabricated to ablate Staphylococcus aureus (S. aureus) biofilm. Upon NIR pulsed laser irradiation, the nanodroplets can gasify to generate destructive gas shockwave, which further potentiates initial acoustic cavitation effect, thus synergistically disrupting the protective biofilm and killing resident bacteria. More importantly, the gasification can further promote antibiotic release in deep biofilm for residual bacteria eradication. The nanodroplets not only exhibit deep biofilm penetration capacity and high potency to ablate biofilms, but also good biocompatibility without detectable side effects. In vivo mouse implant model indicates that the nanodroplets can accumulate at the S. aureus infected implant sites. Upon pulsed laser treatment, the nanodroplets efficiently eradicate bacteria biofilm in implanted catheter by synergistic contribution of gas shockwave-enhanced cavitation and deep antibiotic release. Current phase changeable nanodroplets with synergistic physical and chemical therapeutic modalities are promising to combat complex bacterial biofilms with drug resistance, which provides an alternative visual angle for biofilm inhibition in biomedicine.