Number Of Laser Pulses Research Articles

Analytical 3D modeling of accumulative heating under multipulse laser irradiation of inorganic materials and biological tissues

• Analysis of accumulative 3D heating by laser pulses using Green's function method. • Accumulative heating under the pulse-periodic action of three types of heat sources. • Dynamics of residual temperature of titanium, monocrystalline silicon, dry bone. • Results useful for optimization of technological regimes of irradiation. In this paper, using analytical methods of the theory of thermal conductivity, the issue of accumulative 3D heating under multipulse laser irradiation of inorganic materials and biological tissues is studied. For a number of practically important cases, comparatively simple analytical dependences of the residual temperature on the number of laser pulses and their repetition rate have been obtained. The limits of their applicability are discussed. Examples of the application of the developed theory for specific cases of pulse-periodic laser irradiation of various materials, in particular, titanium, monocrystalline silicon, and bone tissue, are demonstrated.

Morphological and ablation characteristics of brass and fused silica after interaction with ArF excimer laser

This study investigates the interaction of the 193 nm ArF excimer laser with brass and fused silica in the ambient air. The study compares the differences in surface morphology and ablation rate of craters produced in brass and fused silica at different values of fluence and number of laser pulses using optical and scanning electron microscopy. The ablation rate was found to be slightly lower in fused silica than in brass. The ablation rate increased from 180 to 370 nm/pulse in brass and from 120 to 240 nm/pulse in fused silica when increasing the fluence from 6.8 to 15.2 J/cm2. In contrast to fused silica, melting and ejection of molten material were dominant in the ablation of brass. Various shapes and sizes of particles were observed in the debris deposited around the craters created in brass and fused silica. Resolidified particles with sizes greater than 1 µm were observed at and around the crater edges in brass due to the deposition of the ejected liquid droplets. In fused silica, large cauliflower-like particles were observed around the craters. Nano-size particles were also formed in brass and fused silica at low fluence but with a density smaller than that of the large particles formed at high fluence. The threshold fluence calculated from the relationship between ablation rate and fluence was found to be 0.78 and 3.03 J/cm2 in brass and fused silica, respectively.

The Effect of the Number of Laser Pulses on Some Physical Properties Affecting Gas Sensitivity of CdO Thin Films Prepared by PLD Method

In this research, thin films of cadmium oxide (CdO) were manufactured using pulse laser deposition (PLD) technology on glass substrates under pressure of (0.001 mbar) at room temperature by a laser power effect (800mj/cm) with a number of different laser pulses (N= (150-200-250 and 300)). The optical and synthetic properties of thin cadmium oxide films were studied, as well as their gas sensitivity. The optical properties of thin films were analyzed and studied using absorption spectra (UV-VIS) UV-Visible measurements show that CdO films of different thicknesses have a direct permissible transition with the band gap between (2.51) and (2.22) eV before annealing and after annealing the band gap decreases to become between (2.44) and (2.06). As for synthetic properties, they were analyzed and studied through X-ray diffraction patterns which showed the thin films are multicrystalline the grain size increase with the increase in the number of pulses from (100) pulse to (300) pulse gradually as for the effect of annealing, it also led to an increase in the size of the particles. While gas sensor properties were studied using static gas sensor system. The results of gas sensor showed that the increase in operating temperature improves film sensitivity. the maximum sensitivity of the pure CdO film to gas (NO2) was found to be 46.16% at 200°C and the number of pulses was (150). After annealing, the gas sensitivity decreased to was (34.25%) for (150) pulses.

Investigation and correlation between surface modifications and field emission properties of laser-induced silicon plasma ion irradiated stainless steel

Laser-induced silicon (Si) plasma has been used as a source of ion irradiation for modifications in surface, structural and field emission properties of Stainless Steel (SS). Nd:YAG (532 nm, 10 ns) laser at irradiance of 15 GW/cm2 was used to generate Si-plasma ions which were detected by solid-state nuclear track detector (CR-39) and Faraday Cup (FC). Both the energy and fluence of Si ions were measured by FCs. In response to a stepwise increase in the number of laser pulses from 3000 to 12000, the ion fluence varies from 4.6 × 1014 to 18.3 × 1014 ions/cm2 with constant energy of 30 keV. Fourier Transformation Infrared (FTIR) spectroscopy analysis revealed that irradiated silicon makes the stretch band with oxygen Si–O–Si. X-Ray Diffraction (XRD) analysis confirmed the identification of new phase of Si (111) with an anomalous trend in crystallite size, dislocation line density and induced stresses in response to the irradiation with various Si ion fluences. Optical microscopy analysis showed the formation of pits, voids and tracks. Scanning electron microscope (SEM) analysis revealed the formation of nanoscale surface features including pores, craters, embedded particulates and protruded disk-like structures with multiple ablative layers at the fluence of 4.6 × 1014 to 13.7 × 1014 ions/cm2. At the highest ion fluence of 18.3 × 1014 ions/cm2, the flake/flower-like morphology is observed. Field emission (FE) properties were studied under ultra-high vacuum condition in a parallel plate configuration using planar virgin SS as an anode and structured SS as a cathode. The Fowler–Nordheim plots were obtained from I–V characteristics to evaluate the turn-on field, field enhancement factor β and a maximum current density ranging 1.5–4.5 V/µm, 5008–12807 and 96–454 nA/cm2, respectively. The variation in the FE properties is attributed to the different morphological features at varying silicon ion fluences.

Direct single-pass writing of two-phase binary diffraction gratings in a Ge2Sb2Te5 thin film by femtosecond laser pulses

The formation of alternating amorphous-crystalline structures on the surface of Ge2Sb2Te5 thin film upon the single-pass direct writing by a femtosecond laser beam was demonstrated. We obtained high quality periodic surface structures in non-ablative mode and determined the optimal laser fluence, pulse number and scanning speed for their scaling. The produced structures were stripes up to 1-mm long and consisted of up to 50 parallel amorphous-crystalline lines oriented perpendicular to the light polarization. These two-phase binary stripes had a period equal to the recording beam wavelength and exhibited diffraction grating behavior due to remarkable optical contrast. Diffraction spectra were investigated experimentally and also simulated using scalar and vector theory of diffraction.

Capacity retention improvement of LiCoO2 cathodes via their laser-ablation-based nanodecoration by BaTiO3 nanoparticles

We report on the pulsed-laser-deposition (PLD) based nanodecoration of LiCoO2 (LCO) with BaTiO3 (BTO) nanoparticles (NPs) aimed at increasing the density of dielectric-active material–electrolyte triple-phase interfaces (TPIs). The BTO-NPs were deposited onto LCO at different numbers of laser pulses (NLp) and two different schemes, namely, (i) BTO-NP deposition on the surface of the precast cathode (“2D-nanodecoration”) and (ii) BTO-NP decoration of LCO powder prior to its processing to form a working cathode (“3D-nanodecoration”). While the “2D-nanodecoration” mode was found to improve significantly the discharge capacity of the LCO cathodes (by ∼30 mAh/g for NLp ≥ 200), their capacity retention (CR) was modest. In contrast, the “3D-nanodecoration” scheme enabled not only the volumic nanodecoration of the LCO powder by BTO-NPs but also their subsequent annealing to improve their crystallinity. These 3D-nanodecorated LCO cathodes were found to exhibit significantly higher CR values. In particular, for NLp = 100 k, a CR (@10 °C) as high as 78% was achieved (∼47% higher than that of their sol–gel-processed cathode counterparts). Our results point out that three key ingredients (small BTO-NP size, high DTPI, and high dispersibility of NPs on LCO) should be combined to ensure a high CR of BTO-NP-decorated LCO cathodes.

The effect of trophectoderm biopsy technique and sample handling on artefactual mosaicism.

To determine whether embryo mosaicism prevalence in preimplantation genetic testing for aneuploidy (PGT-A) cycles is associated with the trophectoderm biopsy technique used (a. number of laser pulses or b. the use of flicking or pulling) or the time to tubing. Prospective observational study performed in a single IVF-PGT-A setting from May 2019 to May 2021. Trophectoderm biopsies were analysed by next-generation sequencing. Mosaicism was analysed in relation to the biopsy methodology (number of laser pulses and pulling vs flicking), time elapsed from biopsy to tubing (min), and time of sample cryostorage from tubing to amplification (days). As a secondary objective, the number of laser pulses and biopsy methodology were studied in relation to clinical outcomes of transferred euploid blastocysts. None of the analysed variables were associated to mosaicism prevalence. Multivariable regression analysis demonstrated that mosaicism prevalence was comparable either when > 3 laser pulses were used as compared to ≤ 3 (13.9% vs 13.8%, aOR = 0.8726 [0.60-1.28]) and pulling compared to flicking (13.1% vs 14.0%, aOR = 0.86 [0.60-1.23]). Moreover, neither the number of laser pulses during biopsy (> 3 vs ≤ 3) nor the technique used (pulling vs flicking) were associated with clinical pregnancy after the transfer of frozen-thawed euploid blastocysts (54.9% vs 55.2%, aOR = 1.05 [0.53-2.09]; 61.1% vs 52.9%, aOR = 1.11 [0.55-2.25], respectively). Our results suggest that, as long as the biopsy and tubing procedures are performed following standardized high quality procedures, no specific approach would increase the generation of artefactual mosaicism as a result of trophectoderm biopsy. Trophectoderm biopsies should be performed regardless of the methodology but always aiming on minimising blastocyst manipulation.

Electromagnetic origin of femtosecond laser-induced periodic surface structures on GaP crystals.

The formations of different types of laser-induced periodic surface structures (LIPSS) on the surface of GaP crystals with different laser fluence are researched in experiments. The transition from the high spatial frequency LIPSS (HSFL) to the low spatial frequency LIPSS (LSFL) occurred as the number of the irradiated laser pulse increased. The finite difference time domain method combined with the holographic ablation model is used to simulate the LIPSS formation under the irradiation of multiple pulses. Different types of ripples are predicted by the electromagnetic approach. Results demonstrate that the electromagnetic origins of HSFL and LSFL are due to the interference of incident field and the scattering field under the multi-pulse irradiation.

Surface morphological, electrical and mechanical properties of nanosecond & femtosecond laser exposed copper, zinc and cupronickel

Effect of laser irradiation on different properties of copper, zinc and their alloy cupronickel (79% copper, 20% zinc and 1% nickel) is investigated. Experimentation is carried out in two portions. Firstly, polished samples are treated with Nd:YAG laser (1.064 µm, ∼12 ns, 10 mJ) in air at different number of laser pulses (10, 20, 30) by making grid on sample. In second portion of experiment, the samples are irradiated separately by Ti:sapphire laser (800 nm, ∼25 fs, ∼0.012pJ) for different exposure time (30, 60 and 90 min). After laser exposure, the surface modifications, electrical conductivity and hardness are analyzed using optical microscope, four-point probe equipment and Vickers hardness tester respectively. Nanosecond laser exposure causes surface roughness, nonuniform heat conduction from crater to outer edges, formation and melting of ripples and heat-affected zone. Laser irradiation leads to decrease in electrical conductivity of the target materials. Laser treatments causes non-linear increase of hardness inside the target materials.

Experimental analysis of Nd3+:YAG laser-assisted ablation on piston ring surface in an environmentally friendly underwater ambiance

The present work focuses on the nanosecond pulsed Nd3+:YAG laser-assisted ablation on the chromium-coated piston ring surface. The influence of laser pulse energies and the number of laser pulses on dimple size at different ambient conditions such as air, underwater (still condition) and underwater (flowing condition) is studied. An underwater laser ablation setup was developed especially to perform underwater laser machining (surface texturing) aimed at avoiding the metallic vapor pollution formed when the laser beam irradiates the target surface. The dimple diameter was maximum with underwater (still condition) followed by air and underwater (flowing condition) for all the corresponding laser pulse energies. The dimple depth was maximum with air ambiance followed by flowing underwater ambiance and still underwater ambiance for all the corresponding laser pulse energies. In underwater ambiances, the re-deposition layer around the dimple was lesser. A part of the melt pool formed in underwater ambiance (still condition) might be dissolved in water. The remaining melt pool is distributed around the dimple as a thin layer. In the case of the underwater flowing ambient condition, flowing water distributes the re-deposition layer further away compared to the underwater still ambiance. The re-deposition layer was substantially minimized around the dimple in both the underwater laser ablation conditions. An increase in compressive residual stress is observed around the dimple formed in underwater laser ablation both in still and flowing conditions. Though the underwater laser ablation (flowing) is more complex, it is found to be more beneficial compared to ablation in air ambiance.

Laser textured titanium surface characterization

Laser surface texturing has emerged as an environmental technological option and fast developing technique to provide different surface conditions. In order to improve its efficiency, it is necessary to overcome the usual trial and error approach by carefully mastering operating parameters. The present work analyzes the effects of a pulsed nanosecond laser beam on the processing of titanium surfaces. The textured surfaces were characterized using various experimental techniques, including scanning microwave microscopy (SMM). The results show the impact of laser fluence, number of laser pulses and laser dimple pitch on textured surfaces mainly from a morphological (microscopies) and mechanical (XRD and SMM) perspective. The topography was analyzed according to the laser texturing parameters. A model of the cumulative effect of the number of laser pulses has been demonstrated. In addition, laser texturing modifies the surface residual stresses. Laser texturing effects on the surface mechanical state were analyzed by varying the laser texturing parameters and also by comparing isolated textured dimples and textured regions as a whole. Many changes were found such as surface topography and residual stresses, surface changes that need to be characterized and known to provide a better understanding of the performance and operating behavior of the materials.

A study of a silicone film deposited on quartz glass under laser radiation

The paper studies the structure, optical and operational properties of a silicone film deposited on the surface of quartz glass as a result of the action of laser radiation on volatile substances released from a silicone rubber sample in a closed volume. The research was carried out within the framework of the laser multiparameter method and using an original setup, which includes a solid-state neodymium laser with a wavelength of 1064 nm, and laser pulse parameters: energy of 105 mJ, a duration of 11–14 ns, a repetition rate of 10 Hz. A sealed test-cuvette is placed at the output of the laser. A silicone rubber sample is placed inside the test-cuvette. When laser radiation passes through the test-cuvette, volatile substances that are released from the sample over time interact with the laser radiation and create deposition zones on the optical elements of the test-cuvette, which affect the optical characteristics of these optical elements. The topology of the deposition zones was studied using a profilometer. The structural composition of the original silicone rubber and the deposition zone was determined using a scanning electron microscope. The main results show the dependences of the coefficients of the area and attenuation of the deposition zone on the temperature and the number of laser pulses. The elemental composition, color, resistance to the action of the solvent, and the thickness of the deposition zones have been investigated. It was found that with an increase in the temperature and the number of laser pulses, the area and attenuation coefficients of the deposition zones increase, the color does not change, and the resistance to the action of the solvent increases. With an increase in temperature, the deposition zone, initially consisting of micro-fragments, becomes continuous, and with an increase in the number of laser pulses, its thickness increases. The thickness of the deposition zone is unevenly distributed along its diameter. The results obtained can be applied in the development of silicone-containing biochips for health diagnostics and therapy.

Nanosecond laser-induced oriented periodic structures on AlN ceramic

This work presents results on nanosecond laser-induced surface structuring of AlN ceramic. The process under investigation is performed using the fundamental wavelength of Nd:YAG laser system. It is shown that the change of the ambient air pressure from atmospheric one to 10-4 Torr, leads to modification of the surface morphology – from ripples structure with a periodicity of about the incident irradiation wavelength, to an oriented periodic microstructure with a characteristic period in the range 10–15 µm. In all cases when the periodic structures are formed, a clear orientation perpendicular to the incident irradiation polarization is observed. The properties of the oriented periodic microstructures (OPMSs) formed at the lowest pressure condition are studied in more details, as the influence of the processing conditions on their characteristics is presented. It is found that the formation of OPMS requires a minimal laser pulse number and application of laser fluence above certain threshold. The surface of the fabricated structures is conductive, as the performed analyses indicate that the effect is related to presence aluminium in the processed areas. Possible mechanisms of formation of these structures are discussed. Ablation experiments using irradiation at 532 and 266 nm are also reported and discussed. The presented results may have significant impact when laser processing of AlN ceramics is considered, and for the design of structures with potential applications in microelectronics, tribology, and aluminium-based UV plasmonics.

In vivo safety study using radiation at wavelengths and dosages relevant to intravascular imaging.

.SignificanceIntravascular photoacoustic (IVPA) imaging can identify native lipid in atherosclerotic plaques in vivo. However, the large number of laser pulses required to produce 3D images is a safety concern that has not been fully addressed.AimWe aim to evaluate if irradiation at wavelengths and dosages relevant to IVPA imaging causes target vessel damage.ApproachWe irradiate the carotid artery of swine at one of several energy dosages using radiation at 1064 or 1720 nm and use histological evaluation by a pathologist to identify dose-dependent damage.ResultsMedia necrosis was the only dose-dependent form of injury. Damage was present at a cumulative fluence of when using 1720 nm light. Damage was more equivocally identified at using 1064 nm.ConclusionsIn prior work, IVPA imaging of native lipid in swine has been successfully conducted below the damage thresholds identified. This indicates that it will be possible to use IVPA imaging in a clinical setting without damaging vessel tissue. Future work should determine if irradiation causes an increase in blood thrombogenicity and confirm whether damaged tissue will heal over longer time points.

Nanoscale-Resistive Switching in Forming-Free Zinc Oxide Memristive Structures.

This article presents the results of experimental studies of the impact of electrode material and the effect of nanoscale film thickness on the resistive switching in forming-free nanocrystalline ZnO films grown by pulsed laser deposition. It was demonstrated that the nanocrystalline ZnO film with TiN, Pt, ZnO:In, and ZnO:Pd bottom electrodes exhibits a nonlinear bipolar effect of forming-free resistive switching. The sample with Pt showed the highest resistance values RHRS and RLRS and the highest value of Uset = 2.7 ± 0.4 V. The samples with the ZnO:In and ZnO:Pd bottom electrode showed the lowest Uset and Ures values. An increase in the number of laser pulses from 1000 to 5000 was shown to lead to an increase in the thickness of the nanocrystalline ZnO film from 7.2 ± 2.5 nm to 53.6 ± 18.3 nm. The dependence of electrophysical parameters (electron concentration, electron mobility, and resistivity) on the thickness of the forming-free nanocrystalline ZnO film for the TiN/ZnO/W structure was investigated. The endurance test and homogeneity test for TiN/ZnO/W structures were performed. The structure Al2O3/TiN/ZnO/W with a nanocrystalline ZnO thickness 41.2 ± 9.7 nm was shown to be preferable for the manufacture of ReRAM and memristive neuromorphic systems due to the highest value of RHRS/RLRS = 2307.8 ± 166.4 and low values of Uset = 1.9 ± 0.2 V and Ures = −1.3 ± 0.5 V. It was demonstrated that the use of the TiN top electrode in the Al2O3/TiN/ZnO memristor structure allowed for the reduction in Uset and Ures and the increase in the RHRS/RLRS ratio. The results obtained can be used in the manufacturing of resistive-switching nanoscale devices for neuromorphic computing based on the forming-free nanocrystalline ZnO oxide films.

Особенности структурирования и абляции тонких пленок титана фемтосекундными лазерными импульсами

The processes of structuring and ablation of a titanium film by femtosecond laser pulses at wavelengths of 515 nm and 1030 nm have been studied in both single-pulse and multi-pulse modes. The optimal energy regimes for the selective removal of film material without damaging the substrate, as well as the regimes for the generation of the periodic structures on the surface, are determined. The evolution of periodic structures with an increase in the number of laser pulses is shown. The precision removal of titanium film is associated with thermomechanical explosive boiling and the corresponding energy contribution, which ensures the cascade appearance of ablation craters.

Features of structuring and ablation of thin titanium films by femtosecond laser pulses

The processes of structuring and ablation of a titanium film by femtosecond laser pulses at wavelengths of 515 nm and 1030 nm have been studied in both single-pulse and multi-pulse modes. The optimal energy regimes for the selective removal of film material without damaging the substrate, as well as the regimes for the generation of the periodic structures on the surface, are determined. The evolution of periodic structures with an increase in the number of laser pulses is shown. The precision removal of titanium film is associated with thermomechanical explosive boiling and the corresponding energy contribution, which ensures the cascade appearance of ablation craters.. Keywords: thin films, femtosecond laser pulses, surface treatment

On studying the mechanisms and assessing the safety of Nd:YAG laser irradiation of the posterior lens capsule (experimental and clinical study)

To study the mechanisms of laser destruction in exposing the posterior lens capsule (PLC) tissue to Nd:YAG laser irradiation, and to evaluate its side effects on the cornea. The experiment involved 6 autopsy samples of human posterior lens capsule with different optical and mechanical properties, which were exposed to laser irradiation. We used the Nd:YAG ophthalmic laser LPULSA SYL-9000 Premio manufactured by «LightMed» (Taiwan/USA) and an experimental Nd:YAG laser system (1.064 μm). The following parameters were compared: the power of the incident radiation and radiation transmitted through the PLC, the mechanical stresses in the PLC tissue, the kinetic energy of the laser ablation products, and the pressure of gas bubbles during laser exposure in capsule samples of different densities. In the clinical part of the work, the negative effects of Nd:YAG laser on the cornea at different PLC densities were assessed using the endothelial microscope SP 3000P («Topcon», Japan). The experiment showed that in hard samples of PLC there are star-shaped point perforations with a diameter of 50±20 μm with partial rarefaction around the point defects. Damage to soft PLC samples in the form of large complete perforations was up to 200 µm in size. The temperature of laser irradiation necessary to achieve breakdown in soft PLC samples was 90 °C, in hard samples - 120 °C. The results of the experiment indicate that the final outcome - destruction of the PLC tissue - is safer to achieve not by increasing the energy, but by increasing the number of laser pulses. Clinical study results confirm a significant effect of the density of PLC on the values of laser energy and on the state of the cornea after laser intervention. The experimental data on the mechanisms of laser destruction of the lens capsule should contribute to the development of new and improvement of already known technologies aimed at reducing the risks associated with laser surgeries.

Precise and efficient surface flattening of polycrystalline diamond by normal-irradiated trochoidal femtosecond laser machining

The widely used polycrystalline diamond generally requires high smoothness and high efficiency in surface flattening. However, conventional machining methods, such as grinding and polishing, are not capable of processing the polycrystalline diamond with the desired high material removal rate owing to its high hardness, wear resistance and thermal stability. Femtosecond laser is considered an effective machining approach with high precision, but the machining efficiency is not satisfactory in terms of large-scale surface flattening. To further improve the processing efficiency with good surface smoothness, a strategy of normal-irradiated trochoidal femtosecond laser machining (NTFM) was developed in this study to process the polycrystalline diamond with Co binder. The theoretical analysis model, including the accumulated laser pulse number and the distribution of laser energy density, was first deduced for NTFM. The key influent factors were found to be the amplitude of galvanometer and the space between two adjacent laser scanning passes. Then, through machining microgrooves, it is proved that the material removal rate of NTFM was almost twice as high as the conventional non-trochoidal femtosecond laser milling (CFM). Besides, short pulse delay in the NTFM strategy can reduce the heat penetration and inhibit the falling-off of diamond grains. Thus, NTFM strategy is more favorable for generating smooth surface when compared to CFM. It is also found that improving the heat accumulation in NTFM is beneficial to decrease the graphitization level on the machined surface. Finally, a mirror-like large-scale surface of the polycrystalline diamond was successfully processed, with an average roughness of Ra 63 nm and PV value of 0.741 μm by NTFM, taking 30 min or only one-sixth of the time required by CFM. The results indicate that the proposed NTFM strategy is more practical to precise and highly efficient surface flattening of diamond compared to CFM.

Ablation Threshold and Interaction of Cemented Carbide Ablated by Ultrafast Laser

Abstract In this study, we used an ultrafast laser with a wavelength of 1026 nm with the aim of analyzing the ablation threshold and morphologies of the irradiated surfaces of cemented carbide by varying the pulse duration and number of laser pulses. Specifically, we used pulse durations of 0.2, 2, and 10 ps and performed both gentle and strong ablations. For the same wavelength, laser pulse energy, and number of laser pulses, the lowest ablation threshold was 0.2 ps. When we performed a gentle ablation, we observed laser-induced periodic surface structures (LIPSSs) on the entire irradiated surface for all pulse durations. Thus, the pulse duration did not appear to affect the formation of LIPSSs. Strong ablation caused ridges to form at irradiated area outside. When the pulse duration increased, larger ridges were formed, whereas when the pulse duration decreased, coarser ridges were formed. The results obtained by using the ultrafast laser is expected to be helpful in the machining of cemented carbide.