Picosecond Laser Research Articles

Reproduction of Three-Dimensional Microstructures on Inconel 718 Utilizing Laser-Textured PECM Cathodes

Abstract Pulse electrochemical machining (PECM) is an unconventional material removal process, widely applied to machine or shape difficult-to-machine materials. A new concept of reproducing three-dimensional (3D) microstructures has been developed and elaborated. Picosecond laser was utilized to produce concave or convex patterns on PECM cathodes, and pattern replication was carried out to PECM anodes. The laser achieved high machining precision and excellent surface integrity; both patterns were successfully replicated on the anodes. However, considerable deviations were found in the reproduced concave patterns on the anodes, possibly due to the rounding and widening effects.

Linearly Scaling Molecular Dynamic Modeling To Simulate Picosecond Laser Ablation of a Silicon Carbide Crystal.

A molecular dynamics model for picosecond laser ablation of nanoscale silicon carbide crystals was established by linearly scaling the laser focal diameter, and the correlation between the molecular dynamic simulation of the nanoscale and the experimental reproduction of the microscale was achieved. The calculation accuracy of the molecular dynamic model was verified by ablating the surface of silicon carbide wafers with a laser pulse width of 37 ps. On this basis, this paper further investigated the influence of the laser pulse width and fluence on the surface ablation damage and modification width, threshold, and lattice temperature. The results showed that, when the laser pulse width is higher than 10 ps, the silicon carbide damage threshold increases with increasing the pulse width, while the modification threshold is almost unaffected by the pulse width. In addition, the influence of crystal orientation has been studied, and laser irradiation along the [1-100] crystal orientation induces a higher peak temperature, larger damage, and modification width and threshold, followed by irradiation along the [0001] crystal orientation and lowest along the [11-20] crystal orientation. Finally, with the linear scaling value increasing, the spatial distribution of the laser energy field deviates more from the actual situation, resulting in the calculated results being more consistent with the experimental results. Through this paper, it is demonstrated that this linearly scaled molecular dynamics model can be used to study laser ablation results over tens of micrometers.

Research Situation, Hotspots, and Global Trends in Laser Treatment of Acne Scars: A Bibliometric Analysis of Related Research From 2014 to 2024.

Acne vulgaris is a chronic inflammatory skin condition, commonly resulting in acne scars. Treating acne scars remains a significant challenge in dermatology. With advancements in laser technology, its clinical use for treating acne scars has been increasing annually. However, bibliometric analysis on laser treatment for acne scars is lacking. This study aims to use bibliometrics to comprehensively understand the development trends and research hotspots in laser treatment for acne scars. Using "acne scar" and "laser" as search terms, literature on laser treatment of acne scars from 2014 to 2024 was retrieved from the Web of Science Core Collection (WoSCC) database. The literature data were visualized using VOSviewers, CiteSpace, and R software, generating maps of countries, research institutions, authors, journals, references, and keywords. The analysis included 536 articles from 46 countries, with the United States and China leading in publications. Publications focusing on laser treatment of acne scars exhibit a consistent growth trend annually. Key research institutions include Mahidol University in Thailand, Cairo University in Egypt, and Hallym University in South Korea. The "Journal of Cosmetic Dermatology" had the highest number of articles in this field, while "Dermatologic Surgery" was the most cited publication. These publications involved contributions from 2135 authors, with Professor Manuskiatti Woraphong from Mahidol University in Thailand being the most prolific author in this field. Research on the efficacy of laser treatment for acne scars is a major focus in this field. Among the different types of lasers, CO2 lasers are the most commonly used. Emerging research focuses include therapies such as platelet-rich plasma, picosecond laser, trichloroacetic acid, and burn scar. Treatment efficacy is the primary focus of research in the field of laser treatment for acne scars. Platelet-rich plasma, and novel picosecond lasers, have emerged as hot topics and trends in this research field. However, it is important to note that the impact factors of journals publishing in this field are currently low. Therefore, clinicians must consider and explore strategies for publishing high-quality clinical research in the future.

High-power picosecond UV and deep-UV laser sources delivering powers of 30 W at 355 nm, 10 W at 266 nm, and 5 W at 213 nm.

Utilizing LiB3O5, β-BaB2O4 crystals, and an Nd:YVO4 laser with an average power of 70 W and a repetition rate of 100 kHz, we systematically demonstrated and operated high-repetition-rate, high-power, all-solid-state, UV, and deep-UV picosecond laser sources via high-efficiency third-, fourth-, and fifth-harmonic generation (THG, FHG, and FiHG). The maximum output powers of the radiation at 355, 266, and 213 nm reached 31.2, 10.6, and 4.86 W, respectively, and the highest conversion efficiencies from the 1064 nm infrared laser beam to its third, fourth, and fifth harmonics were up to 44.6, 15.3, and 7.16%, respectively. The intensity autocorrelation traces of the generated 355, 266, and 213 nm radiation were measured based on a two-photon absorption (TPA), and the extracted pulse durations were 7.7, 6.1, and 5.9 ps, respectively. This work validates the performance of the β-BaB2O4 crystal in obtaining deep-UV radiation, laying the foundation for compact high-power deep-UV devices. Especially the power of 213 nm radiation may be the highest power, to our knowledge, for the picosecond deep-UV radiation near the wave band of ∼200 nm.

Nano gradient structuring at Ti-6Al-4V surface induced by ultrashort-pulse laser peening

We have successfully fabricated gradient micro/nano structuring on the surface top layers of Ti-6Al-4V alloy using a shock-peening technique facilitated by femtosecond and picosecond laser pulses, without the need for coatings or confinement. These micro/nano structures encompass ultrafine grains, extensive subgrain boundaries, hierarchical nanotwins, and complex dislocation morphologies. The ultrafine grains, ranging in size from hundreds of nanometers to a few micrometers, were predominantly located in the grain-refined regions, whereas the micro/nano dislocation structures were predominantly found in regions of severe plastic deformation. These observations suggest a promising avenue for achieving high-precision gradient structuring in the field of metallic surface engineering.

Effect of different core diameters on the current-carrying performance of CORC cables with REBCO multi-filamentary tapes

The second generation of high temperature superconductivity (HTS) is one of the candidate materials for future superconducting cables (such as CORC), CICC conductors and high field magnets due to its high current carrying performance and excellent mechanical strength. Currently, it has been demonstrated that the utilization of REBCO multi-filamentary tapes in the fabrication of CORC cables can further reduce AC losses. This study involved the preparation of various types of REBCO multi-filamentary tapes through reel-to-reel ultraviolet picosecond laser cutting technology, as well as the manual winding of multiple single-layer CORC cable samples. This work focused on the impact of core diameter on the current-carrying performance of REBCO multi-filamentary tapes under self-field conditions at 77 K. The results indicate that the critical current (IC) of REBCO multi-filamentary tapes decreases as the core diameter decreases. Furthermore, the decrease in IC becomes more significant with an increasing number of cores. When the cable core diameter is 4.6 mm, the critical current of the 3-filament tape is 180.49 A with an n-value of 24.84, which is only a 3.1 % recession compared to the critical current of the commercialized tape. The conclusion of this paper will provide a certain data reference for the subsequent selection of CORC cable core size prepared by REBCO multi-filamentary tapes.

Patchy Dermal Melanocytosis: Differential Diagnosis and Management.

Nevus of Ito and Mongolian spots are distinct clinical presentations of patchy dermal melanocytosis, characterized by similar dermatological manifestations that can pose diagnostic difficulties for clinicians. This review aims to consolidate current understanding and research advancements on these conditions to facilitate clinical diagnosis, differential diagnosis, and management. A comprehensive search of databases including PubMed and Google Scholar was conducted, along with an analysis of pertinent literature retrieved from reference lists spanning nearly four decades. Epidemiological, clinical, and pathological profiles exhibit nuanced differences between the two conditions, with unique expressions under electron microscopy and the regression possibility. It is noteworthy that most Mongolian spots naturally fade with advancing age, in contrast to nevus of Ito, which persist and may potentially evolve into malignant lesions. While picosecond laser treatment has shown greater efficacy than nanosecond lasers, the lower-energy approach holds particular promise in pediatric cases. The therapeutic landscape for patchy dermal melanocytosis is evolving, shifting from selective photothermal action to photomechanical or subcellular photothermal modalities. This review underscores the importance of meticulous clinical assessment and the potential of innovative therapeutic approaches in managing these conditions.

Ultrafast laser-induced simultaneous carbonization and texturization of titanium alloy surface and its tribological properties

Due to the poor tribological properties, the applications of titanium alloy are restricted. Both laser texturing and surface coating are effective methods to enhance the tribological properties of titanium alloy surfaces. Hence, this study proposed a new ultrafast laser-induced simultaneous carbonization and texturization of titanium alloy surfaces to improve its tribological properties by modifying titanium alloy’s surface composition and micro-nanostructures in one step. A polymer film (polyimide, PI) was selected as the carbon source preplaced on the titanium alloy (Ti-6Al-4 V, TC4) surface. On the one hand, under ultrafast laser (picosecond 355 nm laser) irradiation, the laser-induced photothermal effect led to the carbonization of the polymer film and the formation of the pyrolytic carbon coating on the titanium alloy surface. Pyrolytic carbon also reacted with titanium alloy to form titanium carbides. On the other hand, ultrafast lasers also led to the melting and ablation of the titanium alloy surface, creating micro-nanostructures with interlocking micro-holes and micro-bumps. The coefficient of friction (COF) and wear rate of the titanium alloy surfaces were significantly reduced due to the synergistic effects of carbon coating and micro-nanostructures. It showed great significance in improving the tribological properties and the surface treatment of metallic materials.

Quenching high-temperature phase in Cu–Sn alloy system by femtosecond and picosecond laser irradiation

Quenching high-temperature phase in Cu–Sn alloy system by femtosecond and picosecond laser irradiation

Picosecond pulsed laser scribing of Cd2SnO4-based CdTe thin-film solar cells on flexible glass

CdTe photovoltaic modules are the most commercially successful thin-film solar cells. In particular, flexible CdTe modules are a promising development in photovoltaic architecture. Cd2SnO4 (CTO) is a low-cost transparent conductive material with excellent optical and electrical properties. Although laser scribing is commonly used to produce cell interconnects in the manufacturing of thin-film PV modules, the laser scribing process window for CTO-based CdTe cells is narrow, and more research is needed on direct laser scribing of flexible CdTe solar cells. In this study, the picosecond pulsed laser scribing of CdTe solar cells with CTO front electrodes and flexible glass substrates was investigated using lasers with the wavelengths of 355 and 532 nm. The flexible cells were suctioned onto a working platform, and a direct ablation method was adopted. The damage and removal thresholds of the CTO, CdTe, and Ni layers were studied and the effects of the spot spacing, multilayer conditions, and laser polarization state were investigated. A method for determining the scribing parameters was proposed. Very smooth scribing grooves were obtained using the optimized laser scribing process. The series and shunt resistances of the cells after laser scribing showed no significant differences compared to those of the control cells.

Determination of atomic hydrogen density and fluorescence decay time by 1D resolved, picosecond TALIF in the RAID linear device

Abstract We report on the first 1D resolved two-photon absorption laser-induced
fluorescence (TALIF) measurements of atomic hydrogen (H) performed in the
Resonant Antenna Ion Device (RAID) using a picosecond laser system. The
results are obtained across a cylindrical plasma column with peak electron
density 10^18 m^-3 and temperature 1 eV on axis, which decrease monotonically
to 2*10^17 m^-3 and 0.75 eV over a scale of a few cm away from the axis. TALIF
results in these conditions are compatible with a uniform H density profile across
the observed region, with a mean dissociation degree close to 3%. The small
variation of H density across regions covering a wide range of plasma parameters
suggests that transport processes and wall interactions play an important role in
determining the H density profile. The fluorescence decay time is close to 10 ns at
all observed locations, a result compatible with complete substate mixing of the
n = 3 states of H.

Current-carrying properties of REBCO multi-filamentary tapes prepared by reel-to-reel ultraviolet picosecond laser cutting

Abstract REBCO high-temperature superconductors have been widely used in high magnetic field applications, because of their excellent critical current properties and high critical temperature. However, REBCO tape has an extremely large width-to-thickness ratio (typically in the range of 1000–10 000) which causes power dissipation to be too high in applications. One of the most effective ways to reduce AC loss is to divide the superconducting layer in the REBCO tape into filaments. The current-carrying properties degradation behavior of the prepared multi-filamentary tape is the focus of attention. In this study, REBCO multi-filamentary tapes are tested with different numbers of filaments (2-filament, 6-filament, and 10-filament) by cutting the copper-stabilizing layers and superconducting layers through a self-developed reel-to-reel ultraviolet picosecond laser cutting device. The findings indicate that the cut groove has a depth of approximately 30 μm and the width of the groove in the superconducting layer measures around 15 μm. Meanwhile, the research found that ultraviolet picosecond laser cutting does not cause substantial degradation in the I C. Under self-field conditions at 77 K, the I C decreases with the number of filaments, and the degradation of I C is less than 13% in a 10-filament tape, the corresponding decrease of J C is only about 10%. Similarly, at 4.2 K and under various high-field (10 T, 12 T, 14 T) conditions, the I C variation trends of REBCO high-temperature superconducting (HTS) multi-filamentary tapes and non-striated tapes are fundamentally similar, both decreasing as the applied vertical magnetic field increases. Furthermore, it was found that a constant tension of 50 MPa, 100 MPa, and 200 MPa had no effect on the current-carrying properties of the REBCO HTS multi-filamentary tapes.

Industrial picosecond pulse laser welding of stainless-steel to quartz for optical applications

We report on the development of a robust picosecond laser welding process for the industrially relevant material combination of quartz and stainless steel. The process requires high numerical aperture focusing of a 6 ps 1030 nm laser through the transparent quartz onto the interface between the two materials. It is found that increased mechanical pressure applied during welding increases reliability and weld performance and with the correct choice of welding parameters parts will survive ISO standard thermal cycling and vibration testing demonstrating the suitability of the process for industrial application.

Pulse length effects in the nonresonant long-wave infrared nonlinear optical response of n-Ge, GaAs, and ZnSe

Nonlinear optical refraction and nonlinear absorption are characterized in important long-wave infrared optical materials with picosecond and femtosecond laser pulses. The effective nonlinear refractive indices are found to be constant across a range of pulse parameters. Nonlinear absorption far from resonance is observed at relatively low (∼1GW/cm2) intensities in these materials, and the onset intensity and fluence scale strongly with pulse length. A free carrier dominated nonlinear absorption mechanism is identified for picosecond pulses, whereas nonperturbative photoionization causes femtosecond absorption.

Combined Efficacy of Q-Switched 785 nm Laser and Tranexamic Acid Cream in the Treatment of Melasma: A Prospective Clinical Study

Background and Objectives: Melasma, a hypermelanotic dermatologic condition that mainly affects women, poses challenges due to its complex etiology involving environmental and genetic factors. Its pathophysiology, marked by intricate histological changes, is not fully understood. This study explored the efficacy and safety of a new 785 nm picosecond laser in treating facial melasma. Materials and Methods: An 11-participant cohort, comprising women with Fitzpatrick phototypes II-III, underwent a treatment protocol with a new 785 nm picosecond laser. The clinical evaluation used the Global Aesthetic International Score (GAIS) and the Five-Point Likert Scale Questionnaire. The aim of the study was to understand the capacity of the 785 nm wavelength laser to interact with both the pigmentary and vascular components of melasma. Results: The GAIS outcomes revealed excellent (18.2%), good (54.5%), poor (18.2%), and no results (9.1%). The Likert Scale responses varied from very satisfied (18.2%) to slightly satisfied (9.1%). Clinical images at three months demonstrated resolution of melasma with no adverse events. Conclusions: This non-invasive procedure showed positive outcomes and high patient tolerance, emphasizing its potential in melasma management. However, in order to fully understand the interactions of pigmentary and vascular components with the 785 nm wavelength laser, further research is required. The small cohort represents a limitation for this study, therefore studies that include a larger number of patients are needed to assess the effectiveness of this laser treatment for facial melasma.

Numerical study of multi-phase flow in ultrashort pulse laser processing

Ultrashort pulse laser processing is highly valued due to its enormous potential for high micromachining quality while it comprises complicated physical mechanisms especially when the pulse width falls in the regime about 10 ps. This study presents a complete mathematical modeling on multi-phase phenomena in ultrashort pulse laser processing, such as melting, vaporization, and solidification. The volume of fluid (VOF) technique is used to capture the interface during phase transition. Based on this hybrid model, the transport of energy and mass are investigated to study the influence of laser parameters on the formation of laser ablation hole. This work develops the incompressible multiphase laser ablation solver based on PIMPLE algorithm. The calculation results are validated by different references under different laser processing parameters which emphasize the importance of mechanism on thermal ablation and hydrodynamics in picosecond laser processing. More calculation results about the trends in hole depth over pulse laser width, laser fluence, and the number of pulses show the intricate influence of laser parameters.

Picosecond Alexandrite Laser With Diffractive Lens Array Combined With Long-Pulse Alexandrite Laser for the Treatment of Facial Photoaging in Chinese Women: A Retrospective Study.

Facial photoaging is a type of facial skin aging induced mainly by exogenous factors (ultraviolet radiation) and often manifests itself in the form of hyperpigmentation, telangiectasia, roughness, increase in fine lines/wrinkles, and enlarged pores. Recently, picosecond lasers have become an emerging option for the treatment of facial photoaging, and long-pulse alexandrite lasers (LPAL) have demonstrated promising potential in the treatment of photoaging-related symptoms. This study aimed to evaluate the efficacy and safety of picosecond alexandrite laser (PSAL) with diffractive lens array (DLA) combined with LPAL for facial photoaging. This is a retrospective study of 20 Chinese female patients with facial photoaging who received PSAL with DLA combined with LPAL during a 1-year period. All patients were treated every 4weeks for a total of three treatments. Objective indicators of facial photoaging and patient satisfaction were evaluated before each treatment, and pain scores and adverse effects were recorded after each treatment. Compared with baseline, patients showed significant differences in all facial photoaging indices (p<0.01). After receiving three treatments, there was a 20.1% decrease in the pigmentation index, a 23.9% decrease in the erythema index, a 34.5% decrease in the texture index, a 28.4% decrease in the fine lines index, a 56% decrease in the pore index, a 9.3% elevation and a 17.1% decrease in elasticity R2 and F4, respectively, and a 55% decrease in sebum content. The mean satisfaction score for the three treatments was 4.67 (3.33, 5.00), and the mean visual analogue scale (VAS) pain score was 7.00. No serious adverse effects such as post-inflammatory hyperpigmentation (PIH), hypopigmentation, or blistering were observed at the treatment site during the treatment period. PSAL with DLA combined with LPAL for the treatment of facial photoaging with significant efficacy, high patient satisfaction, and minimal adverse effects.

Experimental Proof of the Effect of Induced Optical Coalescence of Bubston Clusters at Water Breakdown Induced by Picosecond and Nanosecond Laser Pulses

Experimental Proof of the Effect of Induced Optical Coalescence of Bubston Clusters at Water Breakdown Induced by Picosecond and Nanosecond Laser Pulses

Establishing laser cutting of components for sulfide-based solid-state batteries

The demand for safe, power- and energy-dense, low-cost batteries is constantly increasing due to the global shift toward renewable energy sources and the associated need for battery electric vehicles and grid-level energy storage. However, current-generation lithium-ion batteries are struggling to meet the requirements and are reaching their physicochemical limits regarding energy density. Solid-state battery technology promises to improve the current state of the art in electrochemical energy storage and has proven itself in research, although not yet in commercial applications. One of the main challenges in bringing the technology to the market is the limited knowledge and research on the production of solid-state batteries with commercially viable technologies. This study investigates the application of laser cutting technology to improve the cutting process in the production of sulfide-based solid-state batteries. Challenges such as the production atmosphere, handling of the components, and differences compared to conventional battery components are discussed. Using a picosecond laser source, the influence of the pulse frequency, peak fluence, scanning speed, and laser passes was investigated to identify appropriate parameters for cutting sulfide-based composite cathodes. The findings were then successfully applied to the cutting of sulfide-based solid electrolyte separators. An improvement in edge quality compared to mechanical punching is demonstrated, marking a crucial step toward the commercialization of solid-state batteries.

Silicon heterojunction back-contact solar cells by laser patterning.

Back-contact silicon solar cells, valued for their aesthetic appeal because they have no grid lines on the sunny side, find applications in buildings, vehicles and aircraft and enable self-power generation without compromising appearance1-3. Patterning techniques arrange contacts on the shaded side of the silicon wafer, which offers benefits for light incidence as well. However, the patterning process complicates production and results in power loss. We employed lasers to streamline the fabrication of back-contact solar cells and enhance the power-conversion efficiency. Using this approach, we produced a silicon solar cell that exceeded 27% efficiency. Hydrogenated amorphous silicon layers were deposited onto the wafer for surface passivation and to collect light-generated carriers. A dense passivating contact, which differs from conventional technology practice, was developed. Pulsed picosecond lasers operating at different wavelengths were used to create the back-contact patterns. The approach developed is a streamlined process for producing high-performance back-contact silicon solar cells, with a total effective processing time of about one-third that of the emerging mainstream technology. To meet the terawatt demand, we developed indium-less cells at 26.5% efficiency and precious silver-free cells at 26.2% efficiency. Thus, the integration of solar solutions into buildings and transportation is poised to expand with these technological advances.