Femtosecond Laser Parameters Research Articles

Optimization of GeSn nanostructures via tuning of femtosecond laser parameters

Semiconductor nanostructures are known to exhibit interesting electrical and optical properties, as well as functionalities that are significantly different from their bulk counterparts. These unique characteristics can be attributed to their quantum confinement effects, and large surface-to-volume ratios, along with the fact that their compositions can be tuned. This study proposes a new method for tuning the properties of GeSn nanostructures on a silicon substrate using femtosecond laser direct writing. A series of GeSn nanostructures with different compositions of Sn ranging from nanodots, nanoholes, nanostrips, nanogaps, and nano-cauliflowers were successfully prepared via tuning of femtosecond laser parameters. The morphology, composition of Sn, and crystalline properties of the formed nanostructures were also greatly influenced by the laser fluence and the effective pulse number. The femtosecond laser/GeSn interaction mechanism was thoroughly investigated based on the two-temperature Drude model. This work provides a novel strategy for tuning the bandgap and morphology of GeSn nanostructures, through which the properties of GeSn-based devices can be tailored according to the requirements of practical applications in the fields of microelectronics and photonics.

Fabrication of three-dimensional microstructures on GaN surfaces through the integration of femtosecond laser ablation and ICP etching

Gallium nitride (GaN) surface microstructures are crucial for enhancing the performance and reliability of high-power devices. However, the direct fabrication of patterned three-dimensional (3D) microstructures on GaN surfaces remains a significant challenge. This paper introduces an innovative approach, employing a maskless femtosecond laser combined with inductively coupled plasma (ICP) etching, to efficiently fabricate petal-shaped 3D microstructures on GaN surfaces. By fine-tuning the ICP etching and femtosecond laser parameters, we have obtained the regularities of the dimensional variations of these 3D microstructures. Additionally, our investigation reveals that the design of microstructural concavity and convexity characteristics can be flexibly manipulated by controlling the ICP etching rate, which is influenced by the oxide content in the laser-modified zone. This study presents a novel method for straightforward fabrication of microstructures on gallium nitride surfaces.

Strain and Temperature Sensing Based on Different Temperature Coefficients fs-FBG Arrays for Intelligent Buoyancy Materials.

The temperature and strain fields monitoring during the preparation process of buoyancy materials, as well as the health status after molding, are important for mastering the mechanical properties of buoyancy materials and ensuring the safety of operators and equipment. This paper proposes a short and high-density femtosecond fiber Bragg grating (fs-FBG) array based on different temperature coefficients fibers. By optimizing the parameters of femtosecond laser point-by-point writing technology, high-performance fs-FBG arrays with millimeter level gating length and millimeter level spatial resolution were prepared on two types of fibers. These were successfully embedded in buoyancy materials to achieve in-situ online monitoring of the curing process and after molding. The experimental results show that the fs-FBG array sensor has good anti-chirp performance and achieves online monitoring of millimeter-level spatial resolution. Intelligent buoyancy materials can provide real-time feedback on the health status of equipment in harsh underwater environments. The system can achieve temperature monitoring with an accuracy of 0.56 °C and deformation monitoring with sub-millimeter accuracy; the error is in the order of micrometers, which is of great significance in the field of deep-sea exploration.

Synthesis and Unique Behaviors of High-Purity HEA Nanoparticles Using Femtosecond Laser Ablation.

High-entropy alloys (HEAs) are a class of metal alloys consisting of four or more molar equal or near-equal elements. HEA nanomaterials have garnered significant interest due to their wide range of applications, such as electrocatalysis, welding, and brazing. Their unique multi-principle high-entropy effect allows for the tailoring of the alloy composition to facilitate specific electrochemical reactions. This study focuses on the synthesis of high-purity HEA nanoparticles using the method of femtosecond laser ablation synthesis in liquid. The use of ultrashort energy pulses in femtosecond lasers enables uniform ablation of materials at significantly lower power levels compared to longer pulse or continuous pulse lasers. We investigate how various femtosecond laser parameters affect the morphology, phase, and other characteristics of the synthesized nanoparticles. An innovative aspect of our solution is its ability to rapidly generate multi-component nanoparticles with a high fidelity as the input multi-component target material at a significant yielding rate. Our research thus focuses on a novel synthesis of high-entropy alloying CuCoMn1.75NiFe0.25 nanoparticles. We explore the characterization and unique properties of the nanoparticles and consider their electrocatalytic applications, including high power density aluminum air batteries, as well as their efficacy in the oxygen reduction reaction (ORR). Additionally, we report a unique nanowire fabrication phenomenon achieved through nanojoining. The findings from this study shed light on the potential of femtosecond laser ablation synthesis in liquid (FLASiL) as a promising technique for producing high-purity HEA nanoparticles.

Сравнительный анализ механического и фемтолазер-ассистированного методов выкраивания лимбальных мини-трансплантатов в эксперименте

Original article Experimental study of manual and femtosecond laser-assisted methods for cutting limbal mini-transplants B.E. Malyugin, S.A. Borzenok, O.N. Nefedova, D.S. Ostrovskii, M.Yu. Gerasymov, A.V. Shatskikh S. Fyodorov Eye Microsurger y Federal State Institution, Moscow, Russian Federation A. Yevdokimov Moscow State University of Medicine and Dentistr y, Moscow, Russian Federation Purpose. To define optimal parameters of femtosecond laser (FSL) (Femto LDV Z8, Ziemer, Switzerland) for cutting limbal mini-transplants to be further used for limbal stem cells (LSC) transplantation and compare the results with manual cutting technique using microsurgical blade. Material and methods. At first step, performed on 3 porcine and 3 cadaveric eyes, the optimal energy parameters of FSL were selected, which ensured the excision of limbal mini-transplants. At the second step, 8 eyes from 4 postmortem donors were used. In the lower and upper parts of the limbus, limbal fragments were cut out into 8 mini-transplants with a FSL (experimental group). Mini-grafts were also formed manually in symmetrical areas of each eye using dosed diamond blade (control group). The structure of the limbal bed after removing mini-transplants was studied by light and scanning electron microscopy. The effect of FSL energy on the viability of LSC was determined by intravital staining using Live & Dead dye. Finally, on the third step, the assessment of reversible and irreversible apoptosis was performed by culturing corneoscleral discs containing mini-transplants not separated from the limbal bed. The obtained samples were cultivated in a medium DMEM/F12 for 7 days followed by immunohistochemical examination. Results. The optimal parameters of FSL operation are determined by energy levels- 100, 110 and 120%. Histological analysis of the limbal residual bed zone showed that the smoothest surface was obtained at energies 110 and 120%. This fact was also confirmed by scanning electron microscopy. When stained with the Live & Dead dye, damage on the lateral and inner sides of limbal mini-transplants was revealed, mainly in the experimental group. After 7 days of cultivation in the cut area in both groups, no expression of apoptosis markers was observed. Conclusion. Cutting out the limbal zone containing LSCs using FSL is safe and allows obtaining limbal mini-grafts. The most optimal parameters of laser operation in the limbal zone were selected – a planar cut at depth of 250 µm using 110% laser energy. Key words: femtosecond laser, limbal stem cells, apoptosis, limbal stem cell deficiency syndrome, scanning electron microscopy, light microscopy, cultivation, histology

Effect of femtosecond laser process parameters on the thermal denaturation degree of skin tissue.

The influence of femtosecond laser parameters on the degree of thermal denaturation was studied experimentally. The relationship between the degree of thermal denaturation and the characteristic parameters of skin microstructure and the secondary structure of skin tissue proteins in characterizing the degree of thermal damage was analyzed. The results showed the interaction of laser power, laser power, and scanning speed had a significant effect on the degree of thermal denaturation; greater degrees of thermal denaturation were associated with larger second-order moments of the texture angle of the skin microtissue and smaller entropy values and contrast, indicating a greater degree of thermal damage; and higher peak temperature, the lower peak intensity of Raman spectra, decrease in the percentage area of α-helix fitted curves and increase in the percentage area of β-sheet and β-turn fitted curves indicate that the protein is denatured to a large extent that means thermal damage is large.

Anatomical and functional results of femtosecond laser-assisted descemet stripping automated endothelial keratoplasty compared to microkeratome-assisted descemet stripping automated endothelial keratoplasty

Abstract Introduction: Femtosecond laser devices have been praised for their precision in corneal surgery; however, their performance in endothelial corneal graft surgery is still in development compared to the standard microkeratome technique. The purpose of this study is to describe the anatomical and functional differences in surgical outcomes between microkeratome (mk) and femtosecond laser (fs) assisted Descemet stripping automated endothelial keratoplasty (DSAEK). Methods: This is an analytic, observational, pilot study of patients who underwent mk-DSAEK or fs-DSAEK. The data were obtained from the clinical records and the institutional transplant registry with a focus on graft measurements, survival, transparency, visual acuity and was further analyzed. Results: A total of 37 participants were included in the study with 70.3% (n = 26) of them being female and 29.7% of them being male (n = 11). Of the 37 eyes, 23 (62.2%) of them underwent mk-DSAEK and 14 (37.8%) of them underwent fs-DSAEK. Optimized femtosecond laser parameters are reported. There was a statistically significant difference in donor graft thickness which was thinner in the fs-DSAEK group with a median of 110 mm interquartile range (IQR) (102.25–117.5) versus a median of 233 mm IQR (219–243.75) P = 0.00 in the mk-DSAEK group. There were no significant differences for other variables between techniques. Conclusion: Fs-DSAEK allowed significantly thinner graft obtention in comparison to mk-DSAEK; however, there were no significant differences between mk-DSAEK and fs-DSAEK in terms of transparency, graft survival, or visual acuity.

Research on the Mass Adding and Removing Combined Mechanical Trimming Method of the Ring MEMS Gyroscope.

The MEMS gyroscope is one of the basic units of inertial navigation, whose performance and accuracy is noteworthy. Because of the limitations of processing technology and other factors, the relative manufacturing error of MEMS gyroscopes is usually large. Errors directly lead to a frequency mismatch of resonant structures and consequently restrict the performance improvement of the gyroscope. This study proposes a mechanical trimming technique combining the addition and removal of gold in a ring MEMS gyroscope. Firstly, the analysis of the gyroscope dynamics and error model and trimming theory provides theoretical guidance for the trimming process. Secondly, the method of adjusting the mass is investigated, and the ablation threshold of femtosecond laser parameters on gold is analyzed, which provides the process with parameters for the trimming experiment. Finally, the frequency trimming process is conducted in three steps, including the addition of gold spheres and the removal of gold spheres and gold film, which are applicable to the trimming process at different rates of frequency split. The results shows that the proposed method can reduce the frequency split of the gyroscope from 4.36 to 0.017 Hz.

WETTABILITY STUDIES ON FEMTOSECOND-¬LASER-TEXTURED N-TYPE SILICON SURFACES

This present study examines the wetting behavior of N-type silicon surfaces that have been textured using a femtosecond laser. By employing three different patterns, i.e., square pillars, micro dimples, and circumferential grooves, and manipulating key femtosecond laser parameters such as laser power (ranging from 8 W to 12 W) and repetitions (ranging from 40 to 60), the wettability properties of the silicon surfaces are modified. The wettability properties of the surface were evaluated by measuring the contact angle by the sessile-drop method using distilled deionized water as a testing liquid. The textured surfaces displayed various wettability characteristics, varying from hydrophilic to hydrophobic. The hydrophobic behavior was observed on surfaces with a peak laser power of 12 W, 60 repetitions, and the lowest pitch of 160 µm. For the square pillar and micro-dimple textures, contact angles of 146° and 120°, respectively, were measured. Conversely, the circumferential grooves exhibited hydrophilic behavior with a contact angle of 20°. These results were achieved at laser powers of 10 W and 8 W, higher pitch values, and increased repetitions. The contact angle decreased with an increase in pitch and a decrease in repetitions and laser power. Based on the experimental findings, it can be concluded that the wettability of silicon surfaces can be controlled for specific applications using a single-step laser ablation technique. The desired wettability characteristics can be achieved by carefully adjusting the key femtosecond-laser parameters and geometrical features.

Influence of Power and Frequency in the Femtosecond Laser Texturing of Ti6Al4V

Laser Surface Texturing (LST) has demonstrated to be the most reliable technique for the micro-modification of surfaces, allowing to obtain taylored surfaces. These modifications, depending on the basic micro-geometry and its repetition pattern, can provide special functionalities to a surface, such as hydrophilicity, hydrophobicity, reflectance, anti-bacterial, ostheo-integrability, as well as custom aesthetic, among others.Nevertheless, when a laser irradiates metallic surfaces, the micro-structure can be modified due to the heat induced, changing the mechanical properties of the surface. To avoid these effects, cold or ultra-short pulsed lasers must be used.A cold laser emits optical pulses with a duration below 1 ps (ultra-short pulses), in the domain of femtoseconds (fs=10-15 s). These ultra-short pulses, combined with high frequencies, in the megahertz region, leads to pulse trains with high repetition rates. This allows the sublimation of the material, keeping it relatively cold due to the short exposition time to irradiation.Ti6Al4V is the most used Ti alloy, thanks to its excellent weight/mechanical properties ratio. Nevertheless, its tribological behavior is very poor. Although there is intense research to improve it by using LST, the study of the influence of femtosecond laser parameters in the desired micro-geometries is still a gap in the scientific literature.In this research, a study of the influence of power (up to 50 W) and frequency (up to 2 MHz) in the fs-laser texturing of Ti6Al4V is presented. Local pulse repetition, linear and surface textures have been studied by combining power and frequency in these ranges, evaluating the geometry obtained by variable focus microscopy. The study carried out has allowed to determine the optimal set of parameters as a function on the target texture geometry, as well as the range in which the LST removal process changes from sublimation (for texturing) to melting (for micro-machining).

Functional Profile of a Customized Wound Parameter in Femtosecond Laser-Assisted Corneal Incision for Cataract Surgery.

To evaluate the performance of optimized parameters of femtosecond laser for cataract surgery corneal incisions regarding opening, patency and surgically induced astigmatism (SIA). Patients scheduled for femtosecond laser-assisted cataract surgery between May 2018 and December 2018 were enrolled. Inclusion criteria were a healthy preoperative cornea and uneventful FLACS. Exclusion criteria were preoperative corneal astigmatism over 1.0 D, previous corneal trauma or pathologies. Clinical data were obtained from the electronic medical records. Surgical planning was based on Scheimpflug tomography images for keratometric data. At postoperative day 60, new keratometric evaluation was performed, obtained using the same device. 101 eyes (61 patients) matched the criteria for SIA analysis. Overall mean SIA was 0.44 ± 0.33 D (0-1.55 D). Axis and size did not have any statistically significant effects on SIA. The overall centroid of the SIA was 0.11. For the opening analysis, was included 156 eyes (79 patients). Successful opening in 87.7% of cases (137 eyes). Temporal incisions had the highest success rate (98.36%). These femtosecond laser parameters showed high opening rates with low opening times. These optimized parameters led to a low incidence of SIA and high predictability regardless of incision site and size. The association between incision opening and SIA was not statistically significant. There was, however, an association between incision opening success and site.

Optimization of Micro-Texturing Process Parameters of TiAlN Coated Cutting Tools by Femtosecond Laser.

Coated cemented carbide currently represents most of all cutting tool inserts due to its unique combination of wear resistance and toughness. Surface texturing technology can give additional performance to reduce the tool’s wear and energy consumption. Using TiAlN-coated cemented carbide tools as the research object, the effects of femtosecond laser parameters (laser energy, scanning speed, scanning times) on the groove morphology of TiAlN-coated tools and the bonding state of coating and substrate were discussed. The study found that when the laser energy was 10 μJ, the scanning speed was 0.7 mm/s, and the number of scans was 5, the groove morphology was ideal, and the coating and the substrate combination remained unchanged. The influence of micro-groove texture on the tool wear mechanism was investigated by cutting test using the micro-groove texture tool produced by this group of process parameters. The flank wear value of inserts with micro-grooved texture decreased significantly by around 25%. This work provides practical data to support the femtosecond laser processing of TiAlN-coated tools. It is helpful to understand further the processing mechanism of a femtosecond laser on the micro-texture of coated tools.

Prediction Model for Liquid-Assisted Femtosecond Laser Micro Milling of Quartz without Taper.

The strong nonlinear absorption effect and “cold” processing characteristics of femtosecond lasers make them uniquely advantageous and promising for the micro- and nanoprocessing of hard and brittle materials, such as quartz. Traditional methods for studying the effects of femtosecond laser parameters on the quality of the processed structure mainly use univariate analysis methods, which require large mounts of experiments to predict and achieve the desired experimental results. The method of design of experiments (DOE) provides a way to predict desirable experimental results through smaller experimental scales, shorter experimental periods and lower experimental costs. In this study, a DOE program was designed to investigate the effects of a serious of parameters (laser repetition frequency, pulse energy, scan speed, scan distance, scan mode, scan times and laser focus position) on the depth and roughness (Ra) of the fabricated structure through the liquid-assisted femtosecond laser processing of quartz. A prediction model between the response variables and the main parameters was defined and validated. Finally, several blind holes with a size of 50 × and a depth of 200 were fabricated by the prediction model, which demonstrated the good consistency of the prediction model.

Femtosecond laser modification combined with chemical etching to achieve high-quality cutting of millimeter-thick fused silica

With the development of technology, fused silica has been widely used in many industrial fields because of its good physical and chemical properties. Especially in the processing and manufacturing of MEMS devices, fused silica has a great application prospect. The actual project puts forward higher requirements for the cutting of fused silica: it can not only ensure the cutting quality, but also be suitable for sample cutting in a wide range of thickness. In order to meet the processing requirements, this paper uses the method of combining femtosecond laser modification processing and chemical etching technology to cut fused silica. The processing parameters of femtosecond laser for modification of fused silica, such as feeding method, laser pulse energy, scanning speed and single feed amount, are mainly explored. The modified sample is etched with 5 % HF solution assisted by ultrasonic wave, and the high-quality cutting of millimeter-thick fused silica is realized, with the steepness of more than 89°, the edge collapse size of less than 2 µm and the cross-section roughness of less than 0.5 µm. This method can be applied to the field of precision machining of femtosecond laser.

Micro/Nano Periodic Surface Structures and Performance of Stainless Steel Machined Using Femtosecond Lasers.

The machining of micro/nano periodic surface structures using a femtosecond laser has been an academic frontier and hotspot in recent years. With an ultrahigh laser fluence and an ultrashort pulse duration, femtosecond laser machining shows unique advantages in material processing. It can process almost any material and can greatly improve the processing accuracy with a minimum machining size and heat-affected zone. Meanwhile, it can fabricate a variety of micro/nano periodic surface structures and then change a material’s surface performance dramatically, such as the material’s wetting performance, corrosive properties, friction properties, and optical properties, demonstrating great application potential in defense, medical, high-end manufacturing, and many other fields. In recent years, the research is gradually deepening from the basic theory to optimization design, intelligent control, and application technology. Nowadays, while focusing on metal structure materials, especially on stainless steel, research institutions in the field of micro and nano manufacturing have conducted systematic and in-depth experimental research using different experimental environments and laser-processing parameters. They have prepared various surface structures with different morphologies and periods with sound performance, and are one step closer to many civilian engineering applications. This paper reviews the study of micro/nano periodic surface structures and the performance of stainless steel machined using a femtosecond laser, obtains the general evolution law of surface structure and performance with the femtosecond laser parameters, points out several key technical challenges for future study, and provides a useful reference for the engineering research and application of femtosecond laser micro/nano processing technology.

Fabrication of Antireflection Micro/Nanostructures on the Surface of Aluminum Alloy by Femtosecond Laser.

Designed micro-nano structures on the surface of aluminum alloy provide excellent light trapping properties that can be used extensively in thermal photovoltaics, sensors, etc. However, the fabrication of high-performance antireflective micro-nano structures on aluminum alloy is challenging because aluminum has shallow intrinsic losses and weak absorption. A two-step strategy is proposed for fabricating broadband antireflection structures by superimposing nanostructures onto microscale structures. By optimizing the processing parameters of femtosecond laser, the average reflectances of 2.6% within the visible spectral region (400–800 nm) and 5.14% within the Vis-NIR spectral region (400–2500 nm) are obtained.

Influence of Pulse Energy and Scanning Speed of Femtosecond Laser on Surface Roughness of SiC Ceramics

Laser polishing, as a novel surface processing technology, has been successfully employed for improving the surface smoothness and geometric accuracy of components for metals, glasses, fibers and ceramics. However, continuous wave and microsecond and nanosecond lasers leads to some undesirable defects of the polished surface, such as heat affected zone, debris redeposition and thermal stress induced microcracks, especially for hard brittle materials. To solve this issue, this article investigated femtosecond laser polishing of SiC ceramics. Influence of pulse energy and scanning speed on surface roughness and surface morphologies was studied. In addition, the relationship between laser parameters and surface roughness and removal depth of SiC ceramics has been revealed. The experimental results indicated that the polished surface without big voids and spalling was obtained through optimizing femtosecond laser parameters.

Low Temperature Processed Fully Printed Efficient Planar Structure Carbon Electrode Perovskite Solar Cells and Modules

AbstractScalable deposition processes at low temperature are urgently needed for the commercialization of perovskite solar cells (PSCs) as they can decrease the energy payback time of PSCs technology. In this work, a processing protocol is presented for highly efficient and stable planar n–i–p structure PSCs with carbon as the top electrode (carbon‐PSCs) fully printed at fairly low temperature by using cheap materials under ambient conditions, thus meeting the requirements for scalable production on an industrial level. High‐quality perovskite layers are achieved by using a combinatorial engineering concept, including solvent engineering, additive engineering, and processing engineering. The optimized carbon‐PSCs with all layers including electron transport layer, perovskite, hole transport layer, and carbon electrode which are printed under ambient conditions show efficiencies exceeding 18% with enhanced stability, retaining 100% of their initial efficiency after 5000 h in a humid atmosphere. Finally, large‐area perovskite modules are successfully obtained and outstanding performance is shown with an efficiency of 15.3% by optimizing the femtosecond laser parameters for the P2 line patterning. These results represent important progress toward fully printed planar carbon electrode perovskite devices as a promising approach for the scaling up and worldwide application of PSCs.

Femtosecond Laser Drilling of Cylindrical Holes for Carbon Fiber-Reinforced Polymer (CFRP) Composites.

Ultrafast laser drilling has been proven to effectively reduce the heat-affected zone (HAZ) of carbon fiber-reinforced polymer (CFRP) composites. However, previous research mainly focused on the effects of picosecond laser parameters on CFRP drilling. Compared with a picosecond laser, a femtosecond laser can achieve higher quality CFRP drilling due to its smaller pulse width, but there are few studies on the effects of femtosecond laser parameters on CFRP drilling. Moreover, the cross-sectional taper of CFRP produced by laser drilling is very large. This paper introduces the use of the femtosecond laser to drill cylindrical holes in CFRP. The effect of laser power, rotational speed of the laser, and number of spiral passes on HAZ and ablation depth in circular laser drilling and spiral laser drilling mode was studied, respectively. It also analyzed the forming process of the drilling depth in the spiral drilling mode and studied the influence of laser energy and drilling feed depth on the holes’ diameters and the taper. The experimental results show that the cylindrical hole of CFRP with a depth-to-diameter ratio of about 3:1 (taper < 0.32°, HAZ < 10 μm) was obtained by using femtosecond laser and a spiral drilling apparatus.

Investigating the correlation between surface wettability and morphology parameters of femtosecond laser processed on YT15

Investigating the wettability of the tool surface made of cemented carbide is of great significance to improve its working life and quality. The micropit array was processed on the surface of cemented carbide YT15 by a 1064 nm femtosecond pulse laser. Then, the optical microscope, the optical profilometer, and the contact angle measuring instrument were applied to measure the surface morphology and the surface contact angle of micropits. The influence of different laser parameters on surface morphology and the surface contact angle was studied. The geometric morphology model of the micropit was established. The influence of the morphology of micropits on the surface contact angle is analyzed based on the Wenzel theory. The results show that the radius and depth of micropits have a positive correlation with the average laser power and scanning times. As the spacing increases, the surface roughness factor and the surface contact angle decrease. There is a strong correlation between the characterization parameters kurtosis, skewness, and surface wettability in a 3D height parameter system. The smaller the kurtosis, the greater the skewness and the better the surface hydrophilicity.