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Highlights • The optimisation of laser ablation efficiency leads to the minimal surface roughness. • Laser ablation rate and efficiency depends on beam scanning speed and hatch distance. • Both-sided 3D objects can be fabricated by the help of the laser ablation. Abstract Solid-state lasers with pulse duration of 10 ps and radiation wavelength of 1064 nm were used to investigate the laser ablation efficiency dependence on processing parameters: laser fluence (pulse energy and beam spot size), beam scanning speed, pulse repetition rate, and scanned line (hatch) distance for the copper sample. Utilising a 40 W power laser, the highest ablation efficiency of 2.5 µm3/µJ and the ablation rate of 100 µm3/µs with the smallest surface roughness of 0.2 µm was obtained. Three-dimensional (3D) fabrication using a galvanometer scanner and layer-by-layer removal technique with optimal parameters defined for efficient ablation were demonstrated at a rate of 6 mm3/min. Combination of high material removal rate with excellent quality and complex 3D structure formation is in a high interest for mimicking bio-inspired surfaces, micro-mould fabrication and decorative applications. [ABSTRACT FROM AUTHOR]

Previous studies have reported altered dentinal structure and properties after laser irradiation. It was the aim of this investigation to determine the thermal and ablative effects of XeCl irradiation in dentin and then to investigate microstructural and physicochemical changes in the residual dentin structure. Extracted human molar tooth roots were bisected and coated with acid-resistant varnish, leaving a window. After irradiation of one half at 1 Hz, 15 ns pulse durations, fluences of 0.5 - 2 J/cm2, both halves were subjected to acidified gelatin gel at pH 4.5. The carious lesions were bisected and used to perform SEM and microhardness measurements.

Previous studies have reported altered dentinal structure and properties after laser irradiation. It was the aim of this investigation to determine the thermal and ablative effects of XeCl irradiation in dentin and then to investigate microstructural and physicochemical changes in the residual dentin structure. Extracted human molar tooth roots were bisected and coated with acid-resistant varnish, leaving a window. After irradiation of one half at 1 Hz, 15 ns pulse durations, fluences of 0.5 - 2 J/cm2, both halves were subjected to acidified gelatin gel at pH 4.5. The carious lesions were bisected and used to perform SEM and microhardness measurements.

A two-dimensional numerical model considering recoil pressure and Hertz-Knudsen ablation rate was established on the foundation of the laser remelting model to investigate the influence of laser processing parameters on crater feature and melted zone, and it was verified through experiments. The temperature and flow velocity distribution of the molten pool during the formation of the crater were analyzed. The results showed that the ablation velocity could be considered under a higher laser peak power density or higher pulse width due to the metal evaporation caused by heat accumulation. The depth and diameter of the crater were significantly affected by laser peak power density and laser pulse duration. Simultaneously, the height of the edge bulge decreased with the increase in pulse duration after 1.5 ms, and the growth rate of central depth was more rapid than that of edge bulge height with the increase of laser peak power density. In the texture with the same depth, a larger melted zone could be obtained with a longer laser duration than the higher peak power density.

Highlights • Laser ablation of Al and Cu targets was performed by using a Q-switched Nd:YAG laser (1064 nm, 10 ns) in deionized water. • The effect of electric field on ablation rate was investigated for two schemes: parallel, and perpendicular to the laser beam. • For both schemes, the applied electric field can increase the material removal rate. • Both crater depth and diameter are strongly dependent on the electric field schemes. Abstract This paper presents the results of experimental study on the effect of electric field on the ablation rate during the nanosecond pulsed laser ablation of aluminum and copper in deionized water. The effect of electric field strength on the material removal rate and its mechanisms were investigated both in the electric field parallel and perpendicular to the laser beam path schemes. The ablation rate was estimated by measuring the dimensions of craters on the target induced by laser. The crater dimensions and optical properties of the produced colloidal nanoparticles were characterized by means of optical microscopy and UV–Vis absorption spectroscopy, respectively. The results indicate that pulsed laser ablation in the presence of an electric field significantly leads to higher material removal rate. The experimental results also confirm that the crater geometry extremely depends on the direction of the electric field with respect to the laser beam direction. The UV–Vis spectra show that the nanoparticles production efficiency increases with increasing the electric field strength. [ABSTRACT FROM AUTHOR]

Highlights • The nanostructures' difference of femtosecond double pulse laser on the three typical materials is studied. • The laser-induced periodic surface structures become very shallow and some nanodroplets are attached to them. • Oxygen atoms cannot be consumed effectively and remain in the materials when the ablation rate is limited. • For fused-silica glass, as the time delay increases, the ablation depth first increases and then decreases. • The overall trend is similar for silicon and stainless alloy. Abstract The ultrashort double-pulse ablation of fused-silica glass, silicon, and stainless alloy is investigated. The time delay between the two pulses ranges from 0 fs to 3 ps. It is revealed that when the ablation rate is limited, the laser-induced periodic surface structures become very shallow and some nanodroplets are attached to them during the double-pulse ablation. In addition, from energy-dispersive X-ray spectroscopy analysis, the oxygen atoms are observed to be not effectively consumed and remain in the shallow nanostructures. On the basis of this, the craters created by the double-pulse laser with different time delays are studied in detail. The results indicate that the method can increase the ablation depth of these materials with certain exceptions. For fused-silica glass, as the time delay increases, the ablation depth first increases and then decreases, while for silicon and stainless alloy, the ablation depth first increases with time delay and then starts to drop after reaching the maximum value. Afterwards it increases again. [ABSTRACT FROM AUTHOR]

The ablation mechanism of thick aluminum film on polyimide by a 1064 nm Nd:YAG laser etching was investigated. By establishing a theoretical model based on interaction of laser and material, the effects of laser parameters including laser power, equivalent laser pulse number, and scanning velocity of laser beam were studied. The results show that when a laser beam with fluence higher than the etching threshold of aluminum irradiated onto the target surface, the etched depth for a single laser pulse is a definite value; the equivalent laser pulse number can be derived when a polyimide plate coated with aluminum film was selected as an object of study. Namely, an optimized etched result can be obtained which corresponds to certain laser fluences and beam scanning velocities. By substituting the calculated results of laser processing parameters into a finite element simulation, the etched results of aluminum film on polyimide could be achieved. The simulated and experimental results present a good coincidence, and the results can be used to set practical laser processing parameters. [ABSTRACT FROM AUTHOR]

Abstract In recent years, it has been shown that ultra-short pulsed lasers can be used for the post processing and the fabrication of cutting tools. This new manufacturing technology can compete with the mainly used grinding process due to its ability to ablate materials independent of their hardness and without any wear. The knowledge of material properties is necessary for an optimal choice of machining parameters and the prediction of the ablation process. Measuring them is challenging, especially for inhomogeneous, ultra-hard materials. In this paper, an industry-relevant method is presented, which enables to determine the threshold fluence and the optical properties of cemented carbide. The required material-specific parameters are derived from simple ablation experiments, which are carried out on a modern laser machining center. Finally, the results are used to present a formula to calculate the material removal rate at different angles of incidence of the laser beam. [ABSTRACT FROM AUTHOR]

Paintings represent composed materials arranged in successive layers. Development of a suitable method for a depth-profiling analysis is essential for acquiring the information on the stratigraphy as well as on the chemical composition of individual layers, revealing the pigments which had been used. In this study, a depth-resolved analysis of multi-layered model samples of historical easel paintings was performed by means of laser-induced breakdown spectroscopy (LIBS) in combination with non-invasive X-ray fluorescence (XRF). The LIBS analysis was carried out using modified laser ablation system, UP-266 MACRO, equipped with a Czerny-Turner spectrometer. The XRF analysis was performed by handheld spectrometer, Delta Premium. In LIBS experiments, a set of six spots was examined with 5, 10, 15, 20, 25 and 30 pulses respectively, for each of the studied paint samples. Digital and 3D optical microscopy was employed to measure individual layer thickness and to obtain the information on average ablation rates of each sample. The chemical composition of the model samples with each layer partly uncovered was known, and this enabled to directly compare the results obtained by LIBS depth profiling with a fast analysis carried out with the handheld XRF spectrometer. The LIBS depth profiling proved to be a suitable method to distinguish layers of a different material composition and estimate their thickness. The combined use of LIBS and XRF analyses offered essential complementary information on the elemental composition of analysed multi-layered samples. [ABSTRACT FROM AUTHOR]

Ultrashort pulse (USP) lasers are widely used for milling, drilling and cutting applications. Their main advantages are the ability to process a broad range of different materials as well as allowing high precision ablation and yield of low surface roughness. However, until now relatively low volumetric ablation rates are obtainable for the USPmilling processes. In the present study, we concentrate on the prediction of the shortest processing time required to ablate a specific geometry in a specific body. For that we discuss possibilities to increase the ablation rate for the application of laser milling of metals. Pulse energy, repetition rate and focal beam size are defined as free parameters of the ablation process thus controlling the ablation rate. The heat accumulation effect in the bulk material and reaching of a critical, material specific surface temperature are assumed to be the limiting factors for the indefinite increase of the ablation rate. An analytical model for heat accumulation during USP laser ablation of geometrically limited bodies is extended to be applied to the process with spatially shaped beams. The thermal limit of the ablation rate is determined by means of the developed model. In order to further develop the process strategy of laser beam stamping, demand for new beam shaping systems and laser sources with high pulse energies is derived from the simulation results. [ABSTRACT FROM AUTHOR]

Ablation thresholds for the metallic elements Ti, Mo, Pt, Au, and Al were investigated using a XeCl excimer laser in the fluence range of 0.1-20 J/cm2. The ablation thresholds were estimated from the dependence of the ablation rate and the diameter of the crater produced by the laser irradiation on laser fluence. Two ablation thresholds obtained from the ablation rate dependence on fluence agreed well with those obtained from the diameter dependence. The lower ablation threshold is related to the threshold calculated using a one-dimensional thermal diffusion model. The results suggest that even at such extremely low ablation rates, melting plays an essential role in excimer laser ablation. [ABSTRACT FROM AUTHOR]

Catastrophic breakdown that occurs during the flight of supersonic vehicles demands more focused research in the insulation of rocket engines. At present, optimization of polymeric ablatives as viable insulation for solid rocket motor casing has a prominent role in the successful mission of rockets. Among polymers, elastomer serves an imperative part. Comprehensive investigations were disclosed, especially in the elastomeric heat shielding materials with various reinforcing agents. In this paper, research progress of mostly used elastomers is reviewed, and a circumstantial understanding about the features of ablation and insulation has been validated. [ABSTRACT FROM AUTHOR]

Laser-induced depth profiling was applied to the investigation of galvanised steel sheets as a typical modern multi-layer coating system for environmental corrosion protection. The samples were ablated stepwise by the use of two different wavelengths of a frequency-converted Nd:YAG-laser, 266 nm and 532 nm, with a pulse duration of τ = 4 ns at fluences ranging from F = 50 to 250 J cm −2 . The emission light of the resulting plasma was analysed as a function of both penetration depth and elemental spectrum in terms of linear correlation analysis. Elemental depth profiles were calculated and compared to EDX-cross sections of the cut sample. A proven mathematical algorithm designed for the reconstruction of layer structures from distorted emission traces caused by the Gaussian ablation profile can even resolve thin intermediate layers in terms of depth and thickness. The obtained results were compared to a purely thermally controlled ablation model. Thereby light-plasma coupling is suggested to be a possible cause of deviations in the ablation behaviour of Al. The average ablation rate h as a function of fluence F for Ni ranges from 1 to 3.5 μm/pulse for λ = 266 nm as well as for λ = 532 nm. In contrast, the range of h for Al differs from 2 to 4 μm/pulse for λ = 532 nm and 4 to 8 μm/pulse for λ = 266 nm in the exact same fluence range on the exact same sample. [ABSTRACT FROM AUTHOR]

Laser induced breakdown spectroscopy (LIBS) has been applied to study ITER-relevant coatings with different surface morphology and crystallinity. LIBS elemental depth profiles were compared with those obtained by secondary ion mass spectrometry (SIMS). Depending on surface morphology and crystallinity, the laser ablation rate of the coatings changed by an order of magnitude, the highest ablation rate had samples prepared by thermoionic vacuum discharge. The inclusion of aluminum (proxy for beryllium) increased the ablation rate by a factor of>6. In addition, for W-Al coatings the ablation was non-stoichiometric. [ABSTRACT FROM AUTHOR]

A number of laser parameters are often regulated to enhance ablation efficiency during laser surgery. As one of clinical treatments, laser removal of benign prostate hyperplasia has been well accepted by surgical urologists. However, due to complex interactions of the surgical parameters, the procedure is still lengthy and dependent upon the surgeon's skill and experience. The aim of the current study is to evaluate the feasibility of response surface method (RSM) to comprehend ablative interactions of multi-parameters and to identify the optimal ablation rate (AR). As a surrogate model in the feasibility study, bovine liver tissue was utilized for ex vivo ablation testing. Three laser parameters pertinent to laser prostatectomy were selected: power (P), treatment speed (TS), and beam spot (BS). As a three-level fractional factorial RSM, Box Behnken design (BBD) was employed to identify the range of each parameter for achieving the optimal AR. The results showed that regardless of TS, AR was linearly contingent on both P and BS due to high irradiance. TS of 6***7 mm/s induced the maximal AR when P of 180Wand BS of 0.4 mm². The corresponding volumetric density energy yielded an ablation volume of 80 mm², which was close to a transition to volumetric saturation. The BBD-based model showed a good agreement with the experimental data in terms of ablation volume. The proposed multivariate parametric analysis can be an efficient designmethod to identify the optimal conditions for laser therapeutics. Further investigations will be performed on prostatic tissue to validate the proposed approach and to explore various optimization processes. [ABSTRACT FROM AUTHOR]

The nail plate forms a barrier that limits the effectiveness of drug delivery in the treatment of nail diseases and prevents the outflow of fluid in the case of subungual hematoma formation. Microperforation of the nail plate through laser radiation can increase the effectiveness of drug delivery and ensure the possibility of blood outflow. This study detected and identified the type and threshold of effects that arise from exposing the nail plate to Yb,Er: Glass ( λ = 1.54 μm) and Er:YLF ( λ = 2.81 μm) laser radiation. The rate and efficiency of nail plate ablation by the radiation of these lasers were studied. The effect of the storage time of a freshly extracted nail plate in open air on its ablation rate by Er:YLF ( λ = 2.81 μm) laser radiation was also investigated. The impact of the Yb,Er:Glass and Er:YLF laser pulses on the nail plate caused bleaching, carbonization, ablation with microcrater formation, and microperforation. The laser energy densities W (thresholds) required for these effects were determined. The maximum ablation rate for Yb,Er:Glass laser radiation was 8 μm/pulse at W = 91±2 J/cm, whereas that for Er:YLF laser radiation was 12 μm/pulse at W = 10.5±0.5 J/cm. The maximum ablation efficiency for Yb,Er:Glass laser radiation was 0.1 μm/mJ at W = 10.5±0.5 J/cm, whereas that for Er:YLF laser radiation was 4.6 μm/mJ at W = 5.3±0.3 J/cm. The laser ablation rate depends on the storage time and conditions of the freshly extracted nail plate. For example, when exposed to Er:YLF laser radiation, the laser ablation rate decreased by half from the initial maximum value in 96 h of air storage and returned to the initial value after 1 h of storage in distilled water. [ABSTRACT FROM AUTHOR]

As the strong thermal effect in the surface, intense pulsed ion beam (IPIB) has been extensively used in material surface modification. The ablation is an important part in the interaction process between IPIB and material. In order to investigate the ablation mechanism, combined with IPIB dynamic energy spectrum and infrared imaging diagnostic results, a two-dimensional axisymmetric heat conduction model considering the effect of ablated material was constructed to describe the ablation process and calculate the lost mass of the targets. The influences of beam parameters and ablated matter on the ablation rate were discussed. The experimental and simulative results of ablation threshold and mass were compared. [ABSTRACT FROM PUBLISHER]

Ablation rates of K9 glass were studied as a function of femtosecond laser fluences. The central wavelength was 800 nm, and pulse durations of 35 fs and 500 fs in air and vacuum were employed. Ablation thresholds of 0.42 J/cm 2 and 2.1 J/cm 2 were obtained at 35 fs and 500 fs, respectively, which were independent with the ambient conditions and depend on the incident pulse numbers due to incubation effects. The ablation rate of 35 fs pulse laser increased with the increasing of laser fluence in vacuum, while in air condition, it slowly increased to a plateau at high fluence. The ablation rate of 500 fs pulse laser showed an increase at low fluence and a slow drop of ablation rate was observed at high fluence in air and vacuum, which may due to the strong defocusing effects associated with the non-equilibrium ionization of air, and/or the shielding effects of conduction band electrons (CBEs) produced by multi-photon ionization and impact ionization in K9 glass surface. The typical ablation morphologies, e.g. smooth zone and laser-induced periodic surface structures (LIPSS) were also presented and illustrated. [ABSTRACT FROM AUTHOR]