Search

Functionalization of single-walled carbon nanotubes (SWNTs) has been reported to tune the photoluminescence (PL) properties of SWNTs. In bioimaging applications, a PL signal excited by near-infrared (NIR) light is preferred because of the high transparency of biological tissues. Although it is missing in dispersed SWNT, chemical functionalization of SWNT using α , α ′ -dibromo-o-xylene (SWNT-xylyl) has been reported to have a new PL peak at 1231 nm, with intense emission upon NIR excitation. In this work, an ultrashort laser pulse was used to investigate the electronic and vibrational dynamics for two samples of SWNT and SWNT-xylyl. Global fitting analysis of the transient absorption spectroscopy data showed that electronic decay dynamics were comparable between the two samples. The transient absorption spectroscopy data measured with the ultrashort laser pulse whose duration is much shorter than the molecular vibration period enabled us to observe the vibration-induced modulation signal in the time domain. A difference between the two samples was found for the dynamics of the G-mode: alkylation by o-xylyl caused a frequency downshift that was not observed in the dispersed SWNTs. It is believed that the G-mode in SWNT-xylyl is initially localized on SWNT, followed by intramolecular vibrational energy redistribution with a time constant of 239 ± 29 fs. [ABSTRACT FROM AUTHOR]

MgAl 2 O 4 and Ti6Al4V, the greatly suitable materials for industrial application, are rarely explored to realize reliable bonding in current research. In this study, the transparent MgAl 2 O 4 and Ti6Al4V were successfully bonded by innovative use of ultrashort pulse laser with ultra-high peak power. The high energy near the laser focus makes MgAl 2 O 4 and Ti6Al4V mix and react with each other after absorbing the laser energy, thus realizing the bridge between them. The homogeneous mixing of all phases was observed in the joint and the newly generated Ti 6 O phase was identified at the interface. In addition, the effects of laser power and scanning speed on the microstructure and mechanical properties of the joint have been thoroughly clarified. This study creatively used femtosecond laser welding as a new mean to realize ceramic-metal joining, which shows great advantages in superior efficiency and precision compared with other welding methods. [ABSTRACT FROM AUTHOR]

Comprehending the laser ablation mechanism is fundamental in determining how diverse laser parameters affect the quality of the ablation process. A finite difference model was developed in this study to investigate the ablation depth and temperature distribution in picosecond ablation process. The investigation involved conducting single-point laser experiments on bronze material using an ultrashort pulse laser with a pulse duration of 12 ps. The experiments were carried out with varying numbers of pulses, ranging from 1 to 80 pulses. The calculated depths of ablations were compared with experimental results. The variation of the ablation mechanism on the workpiece's surface during laser radiation was also investigated. The model established the laser-material interaction mechanisms under different incident pulses. The ionization temperature and ablated material temperature during laser processing are also determined. The results show that for the number of pulses higher than 10, the laser-material interaction changes from Multi-Photon Ionization to ablation, while in lower numbers, there are no effects of thermal damages adjacent to the laser points. The relationship between variations in the ablation depth and changes in the incidence angle was also investigated. As the incidence angle increases, the removal mechanism changes from MPI to the thermal. [ABSTRACT FROM AUTHOR]

The ultrashort pulse laser based on a Cr2+:ZnSe monocrystal has been presented, utilizing carbon nanotubes as a saturable absorber. The saturable absorber consists of a sapphire substrate onto which nanotubes are deposited. Such a structure enables the realization of an element capable of simultaneously functioning as a saturable absorber and as a compensator for intracavity dispersion, as the substrate thickness can be chosen during fabrication, allowing for the adjustment of the introduced dispersion. Several laser resonator configurations are discussed, demonstrating the possibility of generating ultrashort laser pulses with durations down to 160 fs, a repetition rate of 135 MHz, an output power of 17 mW, and a central wavelength of 2.45 µm. [ABSTRACT FROM AUTHOR]

The pulse length for ultrashort pulse lasers is considered shorter than the thermal vibration period of the material lattice. The thermal diffusion depth is negligible when compared with the optical penetration depth because laser-matter interaction occurs only near the focal volume. Hence, ultrashort pulse lasers are indicated for micromachining. This study aims to evaluate straight and zig-zag texture patterns generated by ultrashort laser pulses on the rake face of uncoated cemented carbide tools during the turning of martensitic stainless steel. The tests were performed under dry and lubricated conditions. The output variables were machining force, cutting power, chip thickness ratio and aspects of workpiece quality (form tolerance and surface roughness). The textures presented micrometric dimensions with a narrow deviation. The main results showed that the straight texture pattern decreased the machining force by 17.5% when compared to the zig-zag pattern. For cutting power, the straight pattern reduced consumption by 5.8% and 6.9% in relation to the reference and zig-zag tools, respectively. Finally, under dry machining conditions, the straight tool was able to decrease the workpiece cylindricity deviation by an average of 108% and 25% compared to the reference and zig-zag tools. The results provide evidence that texturing can affect the tribological system, chip-tool interface, with a potential impact on the sustainability of the process. [ABSTRACT FROM AUTHOR]

Micro texturing of injection molds for plastic part functionalization has been of growing interest in recent years. Especially for laser texturing it has been successfully demonstrated at lab scale that microscopic surface features can be replicated in plastics at highest structural precision. This paper focusses on high-rate laser surface texturing of injection mold steel 40CrMnMo7 for injection molding of plastic parts with hydrophobic surface behavior. In this study, an ultrashort pulse laser system was used providing an average maximum laser power of 70 W. At first, the most important process parameters like fluence (0.37 - 2.87 J/cm²) and pulse repetition frequency (PRF, 2 - 16 MHz) were varied in order to determine optimal parameter settings for high quality and high throughput laser machining using a polygon scan system with a scanning speed of 100 m/s. In addition, the influencing effect of the microstructure topography on hydrophobicity was examined. Particularly, the laser texturing of the mold sidewalls was challenging as the processing angle was tilted to 45° that was helpful for defect-free demolding of the injection molded 3D-part. Finally, a whole 3D-injection mold was laser textured for injection molding of a small plastic box with a processed surface area > 40 cm² to prove the feasibility of the process. [ABSTRACT FROM AUTHOR]

This article discusses the process of the laser turning of rotational symmetric, cylindrical components using ultrashort laser pulses with respect to the geometrical conditions and the resulting energy distribution during the laser turning process. As a result, process predictions and potential process optimizations are feasible. Particular attention is drawn to the laser spot formation on the cylindrical surface of the work piece in conjunction with the positioning of the laser beam relative to the rotation axis of the specimen. Based on fundamental calculations and experimental results, an optimum processing strategy is discussed, whereat the use of a trepanning optic in the laser turning process and the forming of a particular surface structure is additionally being issued. [ABSTRACT FROM AUTHOR]

Ultrashort laser pulses are used to generate Laser-Induced Periodic Surface Structures (LIPSS). To apply LIPSS on small confined areas, the laser source must be focused to a small spot diameter. Contrary to commonly used high numerical aperture objectives, we present a Bessel beam-based approach to produce LIPSS covered lines with a width of 4 to 10 µm. Therefore, an 800 nm Ti:Sa-laser with a pulse duration of 110 fs and a repetition rate of 5000 Hz was used. The setup convinces with an extended depth of focus. Thus, high reproducibility of the process was proven, while no focus control and no specific requirements for the surface quality are needed. The applicability of this method is demonstrated by structuring the shell surface of nickel–titanium wires. [ABSTRACT FROM AUTHOR]

Based on the L-S generalized thermoelastic theory and in view of the specific heat capacity change of material with temperature, the control equations for the thermoelastic coupling system with internal heating source were established. The thermomechanical responses of yttrium tetragonal zirconia (YSZ) under the action of ultrashort pulse laser were studied by means of the finite element method. The effects of the specific heat capacity change with temperature, and the pulse width of the laser on the thermomechanical responses and the mechanical wave reflections in material were obtained. The results show that, under repeated pulse laser actions, the stress and displacement of the material will undergo fluctuations, and the mechanical response will be more sensitive to heating than the thermal response. The specific heat capacity change with temperature will result in the decrease of the thermal response. The study provides an important guidance for improving the ultrashort pulse laser machining quality. [ABSTRACT FROM AUTHOR]

Achieving high surface integrity of micro features on the silicon wafers is highly challenging, owing to the inherent material properties like higher reflectivity, brittleness, and low toughness. In the present work, ultrashort pulse laser micromachining is used to create high-depth microchannels in silicon. Utilization of high average power ultrashort pulse laser for producing high-depth microchannels in silicon causes adverse effects on the feature quality. To investigate this, repetition rates from 10 to 500 kHz produce average power from 0.18 to 9 W at a minimum constant pulse energy of 18 μJ and peak fluence of 0.28 J/cm2. Surface integrity is evaluated in terms of surface roughness, melting thickness, and crack formation. The ablation depth of 18.24 μm is obtained in silicon at high average power of 9 W. The influence of heat accumulation is dominant at high repetition rates. The temporal separation between pulses decreases with an increase in repetition rates. This induces residual stress at the ablated region, eventually leading to the formation of a crack. Higher melting thickness, surface roughness, and presence of crack were significantly detected at high repetition rates from 333 to 500 kHz. The optimum surface integrity was obtained at a repetition rate of 200 kHz with a pulse energy of 18 μJ. The outcomes from the present research work are highly significant for manufacturing MEMS components. The fabrication of higher-quality micro-scale features on silicon wafers is still considered the most important area of research due to its wide range of industrial applicability. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Laser slicing technology is a new processing technology to fabricate optical glass lenses by focusing ultrashort laser pulse laser into the glass to form a modified layer. Crack propagation can be generated by forming a modified layer with residual stresses, and three-dimensional machining can be achieved by controlling the crack propagation. The purpose of this study was to elucidate the crack propagation mechanism by the laser slicing of glass. The stress around the modified layer were evaluated using microscopic birefringence evaluation device under various laser irradiation conditions. As a result, it was clarified that crack propagation occurs according to the tensile stress in the modified layer due to volume expansion. The tensile stresses were stronger when the modification layer was densely formed. Using this knowledge, we attempted to fabricate a spherical lens with a diameter of 30 mm and a radius of 100 mm. The stress concentration at the crack edge due to warpage promoted self-crack propagation and successfully produced a spherical lens with a mirror surface.

Femtosecond direct laser writing (FDLW) is a powerful tool for modification of the properties of transparent materials through nonlinear multiphoton absorption. Implementing such a tool makes it possible to fabricate buried optofluidic elements for microfluidic (MF) systems and optical waveguides in glass materials. In this study a novel method for microchannel fabrication in glass was suggested. Microchannels were fabricated by FDLW in two-phase glass followed by chemical etching. We report two types of laser modification of two-phase glass processed material with pronounced refractive index change, and core-cladding-like elements that include a densified core surrounded by a decompressed region and an outer densified shell. Fabricated microchannel prototypes resulted from applying different pulse durations, each with various laser powers and scanning speeds. Chemical etching of two-phase glass in HCl is a procedure to obtain a nanoporous matrix and to clean out the channels. After chemical etching both types of modification resulted in similar microchannels with different width and layer properties. Highly uniform microchannels with high aspect ratio, and a pronounced refractive index surrounding layer were achieved after chemical etching, which could possibly be used as waveguide layers. [ABSTRACT FROM AUTHOR]

Sidewall tapering is one of the main limitations in ultrashort pulse (USP) laser machining and is associated with the beam shape and self-limiting effect. Laser processing with a precession beam is a potential solution to overcome this limitation. A study into the effects of precession parameters on the taper angle in microhole drilling of a nickel alloy is reported in this paper. The effects of three key precession parameters, i.e., incident angle, relative distance between the focuses of the precession and individual beams, and scanning speed, have been investigated in detail. Experiments were performed to drill through holes with aspect ratios up to 20:1 and diameters ranging from 100 to 500 μm over 0.6–2 mm thick nickel alloy substrates. Experiment results showed that all the considered parameters/factors were significant and affected the hole tapering in different ways. In addition, there were important interaction effects between two of the factors, i.e., incident angle and focus position, in some cases. The optimal parameters to minimize the tapering effect are suggested, and the mechanism is discussed in detail. The precession laser machining showed clear advantages in overcoming the limitations to associated with conventional USP laser machining. Fabricating microholes with high geometrical accuracy, i.e., with straight side walls and zero taper angles, is feasible with the use of a precession beam. The results clearly show the potential of precession laser processing and the capabilities that the technology can offer for a range of laser micromachining applications in different industries, such as microelectronics, automotive, and aerospace. [ABSTRACT FROM AUTHOR]

We developed a time-resolved force microscopy technique by integrating atomic force microscopy using a tuning-fork-type cantilever with the delay time modulation method for optical pump-probe light. We successfully measured the dynamics of surface recombination and diffusion of photoexcited carriers in bulk WSe _2 , which is challenging owing to the effect of the tunneling current in time-resolved scanning tunneling microscopy. The obtained results were comprehensively explained with the model based on the dipole-dipole interaction induced by photo illumination.

Processing diamonds using conventional methods poses problems such as significant tool wear and low machining efficiency. Alternatively, lasers are capable of fine diamond processing without tool wear. This study aimed to clarify an efficient irradiation method with top-hat beam modulation for achieving smooth surfaces in the ultrashort pulse laser processing of single-crystalline diamond. Pulses of less than 1 ps helped achieve efficient material removal, and beam expansion with top-hat modulation increased material removal efficiency. Using a top-hat square beam, material removal at 0.00015 mm3/s and 250 nm surface roughness Sa were achieved with a 5 kHz laser frequency. [ABSTRACT FROM AUTHOR]

This article discusses the process of the laser turning of rotational symmetric, cylindrical components using ultrashort laser pulses with respect to the geometrical conditions and the resulting energy distribution during the laser turning process. As a result, process predictions and potential process optimizations are feasible. Particular attention is drawn to the laser spot formation on the cylindrical surface of the work piece in conjunction with the positioning of the laser beam relative to the rotation axis of the specimen. Based on fundamental calculations and experimental results, an optimum processing strategy is discussed, whereat the use of a trepanning optic in the laser turning process and the forming of a particular surface structure is additionally being issued.

We have developed a method of evaluating the photo-induced carrier dynamics of nanostructures by combining optical technologies with multiprobe microscopy techniques. Using multiple probes, measurement can be carried out even for a small sample without complicated pretreatments, such as attaching electrode structures. Using transition metal dichalcogenides as a sample and a continuous laser or an ultrashort pulse laser as the light source, we demonstrated analyses of the carrier dynamics related to trap levels in a millisecond to second time domain and the ultrafast photoexcited carrier dynamics in the picosecond region. [ABSTRACT FROM AUTHOR]

We report on a comprehensive study of laser ablation and micromachining of alumina using a high-power 1030 nm ultrashort-pulsed laser. By varying laser power up to 150 W, pulse duration between 900 fs and 10 ps, repetition rates between 200 kHz and 800 kHz), spatial pulse overlap between 70% and 80% and a layer-wise rotation of the scan direction, the ablation efficiency, ablation rate and surface roughness are determined and discussed with respect to an efficient and optimized process strategy. As a result, the combination of a high pulse repetition rate of 800 kHz and the longest evaluated pulse duration of 10 ps leads to the highest ablation efficiency of 0.76 mm 3 /(W*min). However, the highest ablation rate of up to 57 mm 3 /min is achieved at a smaller repetition rate of 200 kHz and the shortest evaluated pulse duration of 900 fs. The surface roughness is predominantly affected by the applied laser fluence. The application of a high repetition rate leads to a small surface roughness Ra below 2 μ m even for the usage of 150 W laser power. By an interlayer rotation of the scan path, optimization of the ablation characteristics can be achieved, while an interlayer rotation of 90 ° leads to increasing the ablation rate, the application of a rotation angle of 11 ° minimizes the surface roughness. The evaluation by scanning electron microscopy shows the formation of thin melt films on the surface but also reveals a minimized heat affected zone for the in-depth modification. Overall, the results of this study pave the way for high-power ultrashort-pulsed lasers to efficient, high-quality micromachining of ceramics. [ABSTRACT FROM AUTHOR]

Surface modification processes of any metallic structure with the help of laser irradiation are a universal practice. The profoundly focused laser beam is to irradiate on the substrate surface to modify the surface condition for the improvement of the tribological properties in heavy and rouged engineering applications. There is a wide application of pure or raw Ti in the field of the biomedical sector specifically in implants and artificial joint prosthesis. In the viewpoint of the above, the present work determines the thermal characteristic aspect in a pure Ti physical domain by developing a two-dimensional heat transfer approach with the dual-phase-lag (DPL) model under the influence of the ultrashort pulsed laser heating. The physical domain has a Ti nanofilm of the 4 nm length, 2 nm width, and 0.02 nm thickness. A DPL model is developed for analyzing the ultrafast heating, as it is the most potential heat transfer model. The present study has modelled a hybrid analytical analysis comprising of the Duhamel's theorem and the finite integral transform method. This work highlights the essentiality of applications of the DPL heat conduction model over the conventional Fourier's model based on the qualitative assessment. The selection of thermal relaxation time lags was carefully chosen from the existing experimental evidence due to the requirement to reach the melting point temperature of pure Ti. The peak temperature of laser irradiation declines with the increase in the optical penetration depth and laser pulse time. Finally, the competence of the present analysis is validated with the published numerical and experimental works from the engineering accuracy standpoint. [ABSTRACT FROM AUTHOR]

Ultrashort pulsed lasers enable microprocessing of dielectric materials, such as glass, sapphire and diamond, owing to the extremely high intensity. However, it is difficult to achieve precision processing, because damage is inevitably generated around the processed shape. To reveal the mechanism of the damage generation, we developed an imaging system, which combined the pump-probe imaging method and a high-speed camera. The system was used to capture the high-speed phenomena on a timescale ranging from picoseconds to milliseconds during the ultrashort pulsed laser processing. The observed phenomena and numerical analyses indicated that excitation of electrons and propagation of stress waves repeatedly occurred around the processed shape and resulted in damages. The revealed mechanism will contribute to developing a method to inhibit damage generation. [ABSTRACT FROM AUTHOR]

To realize various applications, structuring methods of metal‐halide perovskites are of great importance. Most of the common techniques have focused on thin layers and suffer from limitations for thick layers. But thicknesses of several hundred micrometers are necessary, especially for the application field of medical X‐ray detection. In order to scale perovskite‐based X‐ray detectors from small laboratory devices to realistic product sizes, new manufacturing strategies such as laser cutting are necessary. Here the potential of structuring any configurable geometry out of thick, freestanding methylammonium lead iodide (MAPbI3) wafers with ultrashort pulse (USP) laser at a wavelength of 1064 nm, is shown. A small difference in the laser parameters causes a significant variation of the perovskite from material decomposition to almost no effects. With the chosen parameter set of the USP laser, the MAPbI3 wafer can be shaped so that just slight changes in the morphology and no difference in the X‐ray performance can be seen. This method offers the possibility of scaling up perovskite X‐ray detectors in the future without significant signal loss. [ABSTRACT FROM AUTHOR]

Ultrashort pulse lasers have found widespread applications in precise micromachining. Here, we present our brief perspective on the development of this innovative technology from the 1990s until today. [ABSTRACT FROM AUTHOR]

Abstract Background Loosening of prostheses and functional disorders represent a far-reaching problem in the clinic, and the long-term outcomes are essentially determined by wear. Despite all advances, up to 10% of prostheses still fail after 10 years. In particular, more active patients show increased revision rates. Methods The objective of this thesis is to examine whether the applied microstructures of the articulating surfaces can lead to a reduction in abrasion. Three different structural geometries (dimples, offset lines, grid lines) were defined. In an experimental test setup according to DIN ISO 6474 (Deutsches Institut für Normung, International Organization for Standardization), a tribological test of metal and ceramic pairings was performed using two-dimensional ring-on-disc (RoD) tests. Results In both material groups, the structuring had a positive effect on the wear behaviour. In the ceramic group, an abrasion reduction of 22.6% was achieved. However, it is important to take into account the limited informative value due to the hardness of the material. Two of the three Cobalt-Chrome-Molybdenum (CoCrMo) structure geometries (grids, offset lines) also showed a significant reduction in abrasion compared to the reference group, with a maximum wear reduction of 55.5%. Conclusion By reducing abrasion, surface structuring could be used to extend the life of prostheses and minimise the number of revisions.

In ultrashort pulse (USP) laser ablation, focus diameters in the range of >20 μm are common for microstructuring, but the demand for much smaller structure sizes is rising, especially in the fields of filter technology, surface functionalization, and electronics. However, strong focusing of a Gaussian beam near the diffraction limit is accompanied by a very limited depth of focus, which leads to an extreme increase in process sensitivity. It is often too challenging to meet the necessary precision requirements for the system technology. A potential solution to overcome the problem of the short focus depth is the usage of a nondiffracting Bessel beam that is well known for providing a depth of field in the mm range while allowing the diameter of the central processing spot to be below 1 μm. There are several ways to generate a Bessel beam, but only an axicon is suitable for efficient high-power USP ablation. However, even high-precision manufactured axicons have a round tip resulting in a highly oscillating intensity along the propagation axis. This characteristic is a major obstacle for reproducible and reliable laser nanostructuring of metals. For this reason, reflective axicons were newly introduced to the market. They generate a Bessel beam much closer to the ideal axial intensity distribution. In this paper, we compare the Bessel beam generated by a reflective axicon with that of a conventional axicon in an application-oriented setting. Furthermore, we demonstrate the enormous potential of Bessel beams for surface structuring. [ABSTRACT FROM AUTHOR]

A novel hole-making technique, which combines ultrashort pulse (UP) laser drilling with abrasive flow machining (AFM), has been developed to enhance the surface quality and fatigue resistance of diffusive holes in nickel-based single crystal (NBSC) superalloys. This study conducted a comprehensive analysis of the surface morphology and metallurgical characteristics of the hole wall, evaluated by fatigue testing at elevated temperatures and fractography analysis. The findings demonstrate that AFM can effectively eliminate the solidified debris generated during UP laser drilling, significantly reducing surface roughness and inducing a rounded effect at the outlet acute zone of the diffusive hole. Such improvements have been shown to increase the fatigue life of the holes by up to 50.6 % compared to those without polish. Furthermore, the crystal plasticity finite element method (CPFEM) was employed to investigate the localized stress concentration and the accumulation of plastic slip around the diffusive hole, elucidating the mechanisms behind fatigue failure in NBSC superalloys. The study also discusses the influence of the different hole-making technology on the fatigue properties of diffusive holes, integrating CPFEM results with analyses of surface quality and fatigue fractography. The study conducted in this study can provide valuable guidance for the fabrication of diffusive holes in turbine blades. Furthermore, it can also improve our understanding of the fatigue failure mechanism of diffusive holes in NBSC superalloy. [Display omitted] • A hole-making technology for diffusive hole that includes UP-laser drilling coupled with abrasive flow machining was proposed. • The composite technology can reduce the hole-wall roughness and improve the fatigue life of diffusive holes. • CPFE simulation revealed that the large accumulated plastic strains on stress concentration zone caused the final failure. • The influence mechanism of hole-making technologies on the fatigue behavior of diffusive holes was discussed. [ABSTRACT FROM AUTHOR]

Endoprostheses such as hip replacements are subject to wear. Lubrication of the joint interface plays a key role in the wear process, but the mechanisms of lubrication is challenging to understand. The main issue is the three-body abrasion which leads to a shorter life cycle. In order to improve the life cycle, the surfaces of the articulating components can be modified, for example by pulsed femtosecond-laser microstructuring. By microstructuring of the implant surface, the viscosity of the synovial fluid between the joint can be increased due to the non-Newtonian properties of the synovia. This leads to better lubrication and therefore lower particle abrasion. The objective of this study was to evaluate the impact of different microstructures on the viscosity of a joint fluid substitute. Various microstructures were investigated in a modified rheometer setup featuring a decreased gap size. As a test fluid, a synovial fluid substitute was used. The results show that an increase in the viscosity of the synovial fluid substitute can be achieved by microstructuring. An increase of viscosity of up to 20 % compared to the unstructured reference was observed with ring-structures with a diameter of 100 μm and a depth of 20 μm.

Understanding the laser ablation mechanism is highly essential to find the effect of different laser parameters on the quality of the laser ablation. A mathematical model was developed in the current investigation to calculate the material removal rate and ablation depth. Laser cuts were created on the workpiece with different laser scan speeds from 1 to 10 mm s−1 by an ultrashort pulse laser with a wavelength of about 1000 nm. The calculated depths of laser cuts were validated via practical experiments. The variation of the laser power intensity on the workpiece's surface during laser radiation was also calculated. The mathematical model has determined the laser-material interaction mechanism for different laser intensities. The practical sublimation temperature and ablated material temperature during laser processing are other data that the model calculates. The results show that in laser power intensities (IL) higher than 1.5 × 109 W cm−2, the laser-material interaction is multiphoton ionisation with no effects of thermal reaction, while in lower values of IL, there are effects of thermal damages and HAZ adjacent to the laser cut. The angle of incidence is an essential factor in altering incident IL on the surface of the workpiece during laser processing, which changes with increasing depth of the laser cut. [ABSTRACT FROM AUTHOR]

We tried laser slicing of (100) MgO wafer used as a substrate for heteroepitaxial growth of single crystal diamond. The laser slicing was successful by irradiating the inside of the material with an ultrashort pulse laser and generating a {100} cleavage. However, it was clarified that the cleavage of {100} was excessively extended and deviated from the slicing surface, so that steps of 20 μm were formed on the peeled surface. In order to reduce the kerf-loss, it was necessary to control the cleavage of {100}. Therefore, we proposed a scanning method to control cleavage and its extension. As a result, we succeeded in slicing a 2-inch MgO wafer with a kerf-loss of 30 μm.

Antimicrobial surfaces are important in medical, clinical, and industrial applications, where bacterial infection and biofouling may constitute a serious threat to human health. Conventional approaches against bacteria involve coating the surface with antibiotics, cytotoxic polymers, or metal particles. However, these types of functionalization have a limited lifetime and pose concerns in terms of leaching and degradation of the coating. Thus, there is a great interest in developing long-lasting and non-leaching bactericidal surfaces. To obtain a bactericidal surface, we combine micro and nanoscale patterning of borosilicate glass surfaces by ultrashort pulsed laser irradiation and a non-leaching layer-by-layer polyelectrolyte modification of the surface. The combination of surface structure and surface charge results in an enhanced bactericidal effect against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria. The laser patterning and the layer-by-layer modification are environmentally friendly processes that are applicable to a wide variety of materials, which makes this method uniquely suited for fundamental studies of bacteria-surface interactions and paves the way for its applications in a variety of fields, such as in hygiene products and medical devices. [ABSTRACT FROM AUTHOR]

We demonstrate significant temporal contrast improvement for a petawatt-class Ti:sapphire femtosecond laser by introducing a temporal pulse filter based on a self-diffraction process. A double chirped-pulse-amplification laser system was set up to stretch, amplify and recompress the generated first-order self-diffraction pulse. The maximum energy of 130 μJ has been achieved for one first-order self-diffraction seed pulse. By optimizing the initial chirp value, the spectral bandwidth was slightly broadened for the first-order self-diffraction pulse and the cleaned pulse did not exhibit visible spectral distortions in the air environment. The measurement results for the incident pulse and the recompressed first-order self-diffraction pulse showed that the temporal contrast was improved by seven orders of magnitude, i.e. from ∼105 to ∼1012 at −25 ps before the main pulse. Such a temporal contrast is beneficial for laser-matter interaction experiments with high focused intensity up to 1022 W/cm2. [ABSTRACT FROM AUTHOR]

We present a method to stably weld a copper at lower laser power by blackening the surface. Since the reflectivity of copper is approximately 97% in the infrared range, a precise and stable processing of copper is difficult even at high power using infrared laser. To decrease the reflectivity, we fabricated light-absorbing nano-structure on copper surface using picosecond laser pulses. The structure consists of aggregations of nano-particles, and is capable of absorbing as much as 80% of incident light. We demonstrated that a copper with this structure can be welded using 70% lower irradiation power than a copper without it. Additionally, we theoretically investigated the light-absorbing nano-structure using 3D finite-difference time-domain (FDTD) method. [ABSTRACT FROM AUTHOR]

For the most demanding applications in mold and tool manufacturing, ultrashort pulsed laser structured surfaces sometimes do not meet the requirements for surface roughness. A subsequent polishing step in the same machine with the same beam source offers a time and cost effective solution. The novel approach of ultrashort pulse laser polishing with a pulse duration of τ=10 ps is investigated experimentally and theoretically in the present study. It is shown that a low micro roughness is achieved with a melt pool depth between 1 and 3 µm in hot-working steel 1.2738, which allows a polishing process for surface structures with small and fine geometry features without influencing the structure itself. [ABSTRACT FROM AUTHOR]

This is a study of a robot-controlled ultrashort pulse laser system used for tooth preparation to overcome drawbacks of traditional manual methods, thus improving its quality, precision, and clinical efficacy. Based on the international advanced digital technologies, automation technologies, and medical laser technologies, the entire tooth preparation process was completed autonomously using the robot-controlled ultrashort pulse laser. In the study, 15 extracted human first molars were prepared automatically by the robot system. And the result accuracy was evaluated using software. Compared with the CAD data of standard tooth preparation, the overall average error, preparation depth of the natural tooth preparation, and convergence angle were 0.05–0.17 mm, 2.097 ± 0.022 mm with an error of 0.097 ± 0.022 mm, and 6.98 ± 0.35° with an error of 0.98 ± 0.35°, respectively. The feasibility and accuracy of the robot-controlled femtosecond laser technique for tooth preparation were confirmed. [ABSTRACT FROM AUTHOR]

Background: Loosening of prostheses and functional disorders represent a far-reaching problem in the clinic, and the long-term outcomes are essentially determined by wear. Despite all advances, up to 10% of prostheses still fail after 10 years. In particular, more active patients show increased revision rates. Methods: The objective of this thesis is to examine whether the applied microstructures of the articulating surfaces can lead to a reduction in abrasion. Three different structural geometries (dimples, offset lines, grid lines) were defined. In an experimental test setup according to DIN ISO 6474 (Deutsches Institut für Normung, International Organization for Standardization), a tribological test of metal and ceramic pairings was performed using two-dimensional ring-on-disc (RoD) tests. Results: In both material groups, the structuring had a positive effect on the wear behaviour. In the ceramic group, an abrasion reduction of 22.6% was achieved. However, it is important to take into account the limited informative value due to the hardness of the material. Two of the three Cobalt-Chrome-Molybdenum (CoCrMo) structure geometries (grids, offset lines) also showed a significant reduction in abrasion compared to the reference group, with a maximum wear reduction of 55.5%. Conclusion: By reducing abrasion, surface structuring could be used to extend the life of prostheses and minimise the number of revisions. [ABSTRACT FROM AUTHOR]

High-precision surface profiling is studied by using ultrashort pulse lasers up to 450 W laser powers and 40 MHz maximum pulse repetition frequency. A polygon-mirror based scan system is applied for ultrafast and flexible laser beam raster scanning providing up to 560 m/s laser beam moving speeds. By investigating the high-average power picosecond and femtosecond laser systems in large-area processing, optimum parameter settings are derived with regard to machining quality, efficiency and throughput. In addition, the influence of the focus spot size on top width and tip angle of trapezoidal micro structures (Riblets) is evaluated. Inspired by bionic surface functionalities, the laser made Riblets are tested in a Goettingen-type wind tunnel to identify their effectiveness for aerodynamic drag reduction in turbulent flows. For the optimum Riblet geometries, a maximum total pressure loss reduction of 1.76% is achieved that is remarkable when comparing with literature data. The drag reducing effect of the Riblets is further confirmed by empirical-analytical and CFD analyses showing up to 6.4% skin friction reduction. By taking into account the effective processing time of 6.0 cm/min with potential to be further scaled-up with higher laser powers, ultrafast laser-based Riblet profiling could be a key enabling technology to enhance the operational performance in the energy machinery sector. [ABSTRACT FROM AUTHOR]

Copyright of Light Industry Machinery is the property of Light Industry Machinery Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Today's methods for the inspection of the position of weld seams in glass, which has a decisive effect on the strength and thus on the quality of the permanent bond, are costly and often carried out manually in a destructive manner. The present paper proposes the application of optical coherence tomography to determine the position of the weld seam by evaluation of the signals caused by the voids within weld seams. Blind welds of fused silica and alkali-aluminosilicate glass were investigated, and a method for data evaluation is presented. The method is predominantly suitable for glass that exhibits the formation of distinct voids during welding and provides an approach for online monitoring and control of glass welding processes. [ABSTRACT FROM AUTHOR]

Quality and throughput of laser material processing are influenced by multiple laser parameters as well as material properties. Since material degradation due to laser processing is generally related to heat-affected zone, quick optimization and realization of nonthermal process is one of the most important issues for higher-grade laser processing. In this work, we developed various parameter-controlled ultrashort pulse laser system that can control various laser parameters over a wide range, such as pulse duration over three orders of magnitude. Using this laser system (wavelength: 1033 nm, pulse duration: 0.4 to 400 ps, repetition: up to 1 MHz), we have investigated nonthermal–thermal processing boundary in drilling of ceramics: aluminum nitride (AlN) and yttria-stabilized zirconia (YSZ), with high and low thermal conductivity, respectively. As a result, the AlN ceramic exhibited strong dependence of ablation rate on fluence: low-, mid- and high-fluence regimes appeared with different logarithmic correlations. Further, the nonthermal–thermal process boundaries appeared, depending on the pulse duration. On the other hand, the ablation behavior of YSZ was much different from AlN; the ablation rate did not show distinct three regimes. Further, there were no nonthermal process windows for the YSZ. Therefore, the nonthermal–thermal process boundaries were governed by the laser parameters like pulse duration as well as the material thermal conductivity. [ABSTRACT FROM AUTHOR]

The standard preparation technique for micro-sized samples is focused ion beam milling, most frequently using Ga+ ions. The main drawbacks are the required processing time and the possibility and risks of ion implantation. In contrast, ultrashort pulsed laser ablation can process any type of material with ideally negligible damage to the surrounding volume and provides 4 to 6 orders of magnitude higher ablation rates than the ion beam technique. In this work, a femtosecond laser was used to prepare wood samples from spruce for mechanical testing at the micrometre level. After optimization of the different laser parameters, tensile and compressive specimens were produced from microtomed radial-tangential and longitudinal-tangential sections. Additionally, laser-processed samples were exposed to an electron beam prior to testing to study possible beam damage. The specimens originating from these different preparation conditions were mechanically tested. Advantages and limitations of the femtosecond laser preparation technique and the deformation and fracture behaviour of the samples are discussed. The results prove that femtosecond laser processing is a fast and precise preparation technique, which enables the fabrication of pristine biological samples with dimensions at the microscale.

Inspired by the outstanding mathematical breakthroughs of Zhukovsky (2016-2018) regarding the exact analytical solutions of heat equations applicable to flash laser-matter interaction and, on the other hand, by huge progress, both experimental and theoretical, in the area of the ultrashort pulse lasers, we discuss in the present paper the limits of the two temperature model (TTM). We try to extend the TTM from thermal effects during laser metal interaction at femtosecond scale to the metal interaction with attosecond laser pulses. The main result of our theoretical work is that the proposed TTM gives us the same results as the very complex quantum interaction models. In other words, the heat equation from femtosecond laser-metal interaction becomes at the level of attosecond scale a quantum interaction model between metal and laser pulses. We present the computational plot of thermal field for 200 as and 2 fs laser pulse interaction with a 20 × 20 μm² Cu surface. The main result of our work is that somewhere between 200 as and 2 fs laser pulse, the TTM breaks-down, even for a very energetic and very powerful laser beam. [ABSTRACT FROM AUTHOR]

Laser processing of silicon, as the most important material for microelectromechanical systems (MEMS), is commonly known and accepted as an effective manufacturing method to fabricate complex and precise micro components. Especially for the fabrication of micro hole grids, the recently developed high pulse repetition frequency (PRF) laser micro drilling technology is a valuable alternative to standard processing techniques. This paper discusses laser percussion drilling of silicon using ultrashort laser pulses at high average powers with the aim to drill through a material thickness of 100 µm. The main process influencing parameters, such as PRF and laser fluence were varied in order to identify optimal parameter settings for high quality and high throughput micro hole drilling. Furthermore, the effect of additional laser pulses, irradiated after drilling through, onto the micro hole geometry was examined. It will be shown that with increasing PRF and thus, lower laser fluence as a result of constant average laser power of the used laser system, the drilling time decreases significantly. This might be due to thermal accumulation induced by the applied highly-repetitive pulses, leading to a higher substrate temperature which, in turn, lowers the energy needed for melting and evaporation. Surprisingly, this effect results in higher quality of the micro hole geometry without considerable debris at both, hole entrance and exit. [ABSTRACT FROM AUTHOR]

• 2-D instantaneous imaging of laser-induced photoacoustic wave. • Realization and verification of rigorous single pulse interferometry eliminating the background noise by spontaneous emission. • Single pulse and single shot imaging to obtain the entire phase map. • Ultrashort pulse imaging with sub-picosecond duration and large field of view. We perform ultrafast optical imaging by means of single pulse interferometry (SPI) using sub-picosecond ultrashort laser pulses. Laser-induced photoacoustic waves propagating at the sonic speed are captured in 2-D instantly without time-consuming area scanning or averaging-out of electronic noise. A common digital camera offering merely a millisecond-scale exposure is employed in synchronization with pulse picking so as to receive only a single pulse per camera frame. High fringe visibility is obtained with low background noise by blocking asynchronous spontaneous emission (ASE) mixed in source pulses by second harmonic filtering. Our proof-of-concept experimental scheme permits a 0.25 ps effective exposure time with almost ideal image contrast by optical coherence pulse gating. The 2-D ultrafast imaging capability is evaluated through a pump-probe measurement of a 60.8 MHz laser-induced photoacoustic wave in liquid. [ABSTRACT FROM AUTHOR]