Laser Processing Research Articles

Hierarchical Micro/Nanostructures with Anti-Reflection and Superhydrophobicity on the Silicon Surface Fabricated by Femtosecond Laser.

In this paper, hierarchical micro/nano structures composed of periodic microstructures, laser-induced periodic surface structures (LIPSS), and nanoparticles were fabricated by femtosecond laser processing (LP). A layer of hydrophobic species was formed on the micro/nano structures through perfluorosilane modification (PM). The reflectivity and hydrophobicity's influence mechanisms of structural height, duty cycle, and size are experimentally elucidated. The average reflectivity of the silicon surface in the visible light band is reduced to 3.0% under the optimal parameters, and the surface exhibits a large contact angle of 172.3 ± 0.8° and a low sliding angle of 4.2 ± 1.4°. Finally, the durability of the anti-reflection and superhydrophobicity is also confirmed. This study deepens our understanding of the principles of anti-reflection and superhydrophobicity and expands the design and preparation methods for self-cleaning and anti-reflective surfaces.

Reusable SERS Platform of Femtosecond Laser Processed Substrate for Detection of Malachite Green.

This study presents the development of highly efficient Surface-Enhanced Raman Scattering (SERS) substrates through femtosecond (fs) laser processing of crystalline silicon (Si), resulting in mountain-like microstructures. These microstructures, when decorated with gold nanoparticles (Au NPs), exhibit remarkable SERS performance due to the creation of concentrated hotspots. The enhanced Raman signals originate from the excitation of localized surface plasmon resonance (LSPR) of the Au NPs and the multi-scale rough morphology of the Si substrates. Finite-element method simulations confirm the electromagnetic field enhancement in narrow gaps, supporting the experimental observations. The fabricated substrates show high uniformity, oxidation resistance, long-term stability, and exceptional reproducibility, making them ideal for molecular detection, especially in food safety applications. A remarkable enhancement factor (EF) of 1010 is attained in the detection of Malachite Green (MG), boasting a limit of detection (LoD) as low as 10-14 M. This underscores the immense potential of this technique for achieving highly sensitive and dependable SERS-based sensing capabilities.

Alternative Treatments for Zirconium Oxide to Compare Commonly Used Surface Treatments to Determine Which Has the Least Effect on the Phase Transformation.

Traditional mechanical processing of zirconium leads to an unfavorable transformation, from a metastable tetragonal phase to a monoclinic phase (t→m), which weakens the structure of the material and subsequently leads to damage to the prosthetic restoration. The aim of this research is to compare commonly used surface treatments to determine which has the least effect on t→m. Thirty cylindrical samples made of sintered zirconium were divided into six groups based on the following treatments: polishing, grinding, sandblasting, chemical etching, laser structuring or dry plasma etching. After surface treatment, the samples were subjected to the following tests: X-Ray Diffraction, microscopic examination, surface wettability and surface roughness measurements. Chemical etching, laser structuring and plasma etching significantly reduce the content of the monoclinic phase. All surface treatments significantly reduced the final amount of the monoclinic phase. However, chemical etching did not provide sufficient surface roughness. Both laser and plasma processing offer the advantage of creating structural patterns on the surface of elements. However, as plasma etching requires a mask to obtain the appropriate pattern on the surface, it seems that laser processing offers more and varied structuring possibilities. Laser structuring is easier to control and more economical than the other methods.

Investigation of Galvanometer Scanner Failure During the Laser Processing of High Reflectivity Materials and Concrete Composite Materials

Investigation of Galvanometer Scanner Failure During the Laser Processing of High Reflectivity Materials and Concrete Composite Materials

Investigation of ablation threshold and microchannel fabrication on stainless steel using ultrafast laser

ABSTRACT Ultrafast laser processing is a highly versatile tool for creating microscale structures in many materials. The ablation and micromachining characteristics of AISI 304 stainless steel were examined using a femtosecond-pulsed laser. Parameters such as power, scanning speed, transverse overlap, scanning strategies, and shielding gases were systematically varied. The ablation threshold fluence for SS 304 was calculated as 0.16 J/cm2. Two ablation regimes were observed: the gentle regime, where smooth crater walls were formed under low pulse energy (below 20 µJ), and the strong regime, characterized by rough walls created under high pulse energy (above 20 µJ). The optimal parameters for fabricating microchannels on SS 304 surfaces comprised a laser power of 100 mW, a scanning speed of 30 mm/s, a line-to-line distance of 5 µm, and a parallel scan strategy along the major axis. This study provides a practical approach for enhancing the microchannel fabrication process on stainless steel.

Concept of a Cyber–Physical System for Control of a Self-Cleaning Aquaponic Unit

The article aims to present a cyber–physical system (CPS) to support the cultivation of aquaculture in a closed aquaponic system using the deep-water culture (DWC) method. The CPS uses precision sensors as TriOxmatic 700 IQ (for dissolved oxygen and water temperature), AmmoLyt Plus 700 IQ (for ammonium), NiCaVis 701 IQ NI (for nitrites and nitrates), SensoLyt® 700 IQ (for pH), and SL-M5 (for water level). It is built with a Raspberry Pi 4, 8 GB as a server, OpenHAB 3.0 software, and other specialized software for measuring water parameters. Some of the parameters are maintained completely autonomously, while others are indirectly controlled. Basic knowledge of hydroponics and aquaculture is required to set up the system, but day-to-day maintenance can be carried out by employees who receive instructions from the CPS. A method for the physical modification of the fish tank surface by using laser processing is proposed. This results in a change in surface topography (creating diverse microstructure patterns) and its roughness, which is of crucial importance for the bacterial adhesion mechanism.

Temperature-compensated optical fiber sensor for urea detection based on the femtosecond laser-inscribed process

This study demonstrates a low crosstalk temperature-compensated fiber-based urea sensor based on the hybridization of surface plasmon resonance (SPR) and Mach-Zehnder interferometer (MZI). In this sensing structure, an inscribed waveguide and a semi-open cavity are processed by a femtosecond laser in an optical fiber to excite an SPR signal sensitive to refractive index (RI) and an MZI signal highly sensitive to temperature. Based on the temperature detected by the MZI, the influence of temperature on the SPR signal’s RI detection can be calculated and compensated for using a sensitivity matrix. Based on this precise RI detection of the SPR signal, we have achieved selective urea detection by bio-functionalizing the sensor surface using the urease self-assembly method. The sensitivity and limit of detection for urea are 7.98 (nm/mmol/L) and 0.13 mmol/L, respectively, which are better than those in previous studies. Compared to previous temperature compensation studies, this SPR + MZI sensing method using femtosecond laser processing significantly improves the temperature sensitivity of the MZI signal, which reduces crosstalk and ensures a sufficient working range for the SPR signal. Therefore, this sensor is crucial for advancing high-precision temperature compensation detection, high-sensitivity biological detection, and the future application of the femtosecond laser technology.

Enhanced superhydrophobicity of acrylic polyurethane coatings by femtosecond laser ablation

In recent years, superhydrophobic coatings on aircraft surfaces have garnered significant attention due to their ability to protect the surface from corrosive source like raindrops, sand, and gasoline, etc. However, to date, research on enhancing the hydrophobicity of commercial aviation coatings on aircraft Al surface is still insufficient. In the present study, the femtosecond laser ablation technique is used to texture acrylic polyurethane coatings (denoted as APU) which has been used in the aviation field to achieve a superhydrophobic surface. The relationship between micro-/nanostructures fabricated on the coatings under different laser processing parameters and the corresponding hydrophobicity was studied. The microcone-structured superhydrophobic APU surface prepared under the optimal parameters exhibited a contact angle of 151.2° and a sliding angle of 4.2°. Durability test results show that the APU surface remains at a contact angle of more than 150° after a 140° high-temperature test and 6 h acid-base solution immersion, indicating good chemical and thermal stability. The adopted femtosecond laser fabrication technology and the resultant superhydrophobic coating in the present study may have potential applications to protect aircraft parts from corrosion damage.

Enhanced drag reduction of superhydrophobic coatings with femtosecond laser processing and TEOS/KH-SiO2/SA hybridization: CFD simulation and particle image velocimetry

Superhydrophobic surfaces have gained significant attention due to their potential applications in reducing frictional drag in various fluid flow systems. These surfaces mimic the lotus leaf's natural water-repellent properties, resulting in minimal contact between water droplets and the surface. The F-L@TEOS/KH-SiO2/SA coatings are developed using a combination of femtosecond laser ablation and chemical modification with tetraethyl orthosilicate (TEOS), KH550-modified SiO2 (KH-SiO2), and stearic acid (SA). The micro-nano structures formed on the surface enhanced its hydrophobicity, with a contact angle (CA) of 165.94°and sliding angle (SA) of 2.35°. The drag reduction performance is evaluated through experimental methods, including particle image velocimetry and gravity-driven motion analysis, as well as numerical simulations using computational fluid dynamics (CFD). Results showed that the superhydrophobic surface significantly reduced drag compared to untreated aluminum, with an average drag reduction ratio of 10.4 % in experiments and a calculated reduction rate of 9.86 % in simulations. The presence of micro-nano structures promoted the formation of an air layer at the solid-liquid interface, decreasing friction and enhancing slip flow. Additionally, the biomimetic surface generated turbulence at specific distances, aiding in energy dissipation and further reducing resistance. These findings demonstrate the potential of superhydrophobic coatings for applications requiring reduced fluid resistance, such as in marine vessels, pipelines, and fluid transport systems.

Theoretical investigation of multipulse femtosecond laser processing on silicon carbide: ablation, shielding effect, and recast formation

In this study, we propose a transient multi-physics coupling model for ultrafast laser ablation based on the material point method (MPM). By employing the continuum assumption for material, heat transfer equation and particle phase change, as well as spatial discretization of the model, we achieve simulations of various coupled physical phenomena such as material temperature, phase change, stress, and recast layer formation. In terms of time, we simulate laser processing processes with up to 1000 pulses. The model is validated by comparing with experimental results on ablation morphology, recast layer formation from melted particles, and surface oxidation. The proposed model accurately captures the multi-physics aspects of ultrafast laser ablation processes in SiC ceramics. The experimental validation confirms the model’s reliability and offers valuable insights into the underlying physical phenomena.

Femto-Laser Processed Metasurface With Fano Response: Applications to a High Performance Refractometric Sensor

The practical development of compact modern nanophotonic devices relies on the availability of fast and low-cost fabrication techniques applicable to a wide variety of materials and designs. We have engraved a split grating geometry on stainless steel using femtosecond laser processing. This structure serves as a template to fabricate efficient plasmonic sensors, where a thick gold layer is grown conformally on it. The scanning electron microscope (SEM) images confirm the generation of the split laser-induced periodic spatial structures. The optical reflectance of our sensors shows two dips corresponding to the excitation of surface plasmon resonances (SPRs) at two different wavelengths. Furthermore, the asymmetric shape of these spectral responses reveals a strong and narrow Fano resonance. Our computational electromagnetism models accurately reproduce the reflectivity of the fabricated structure. The spectral responses of both the simulated and fabricated structures are fitted to the Fano model that coherently combines the narrow SPRs with the broad continuum background caused by diffraction. The parameters extracted from the fitting, such as the resonance wavelengths and line widths, are used to evaluate the performance of our device as a refractometric sensor for liquids. The maximum sensitivity and figure of merit are 880 nm/RIU and 80 RIU−1, respectively. Besides the compact design of our sensing device, its performance exceeds the theoretical maximum sensitivity of a classical Kretschmann setup.

Control of Orientation and Periodicity of Laser‐Induced Surface Structures on Metals

AbstractLaser‐induced periodic surface structures (LIPSS) can be created on various materials, and they hold an exceptional potential for surface nanopatterning, enabling new industrial applications in medicine, biology, optics and other fields. However, LIPSS formation is typically restricted to a specific orientation and periodicity. In this work, a novel approach is demonstrated for full control of the LIPSS periodicity and orientation on metallic surfaces using a 1064 nm nanosecond laser. Analytical expressions and experimental verification are presented to show that by simultaneously manipulating three parameters of the laser beam, such as the polarization, angle of incidence, and direction of the laser scan along the surface, LIPSS can be formed with the desired geometrical configuration. This enhanced control opens vast possibilities for laser processing technologies as a flexible and highly competitive solution for advanced applications relying on surface modifications in the fields of anisotropic surface wettability, thermal and electrical conductivity, structured colors, diffraction gratings, and many others.

Effect of laser drilling process on combustor liner effusion hole quality

Abstract Effusion cooling is one of the significant cooling technologies in combustor liners in terms of cooling efficiency and weight reduction. However, effusion cooling technology is difficult to manufacture. In fact this technology requires laser-drilling of thousands of tiny holes with shallow angles on a sheet metal with a thickness generally varying between 0.5 to 1.5 mm. In addition, the use of thermal barrier coating is common in gas turbine engines and is one more challenge for the drilling process. In order to obtain more efficient gas turbine engines, the inlet temperature keeps increasing in the last decades, which induces the combustion chamber to operate in a hotter environment. Therefore, efficient cooling technology is needed, even if it is hard to manufacture. For laser drilling, several parameters have to be explored to obtain acceptable holes. This study includes the microstructure investigations of the holes produced with different laser parameters and the optimal laser parameters determined according to the microstructure of six different effusion cooling hole configurations. The results show that laser process differences affect the metal substrate microstructure and thermal barrier coating structure. Drilling method, peak power, number of pulses, gas type and pressure value have a significant effect on the hole geometry and its microstructure.

Hydrophobic surface texture air-liquid phase composite assisted laser processing and tribological properties

In order to improve the surface hydrophobicity and tribological properties of 304 stainless steel, this study used laser processing technology to prepare three types of surface textures (CSA, CM2, CM5) in an air and air–liquid composite environment. By testing the surface quality, wettability and tribological properties of the texture, it was found that the surface quality and interfacial friction control ability of CSA were poor due to the influence of the processing environment. However, due to the air–liquid composite assisted laser preparation, while using the air medium laser processing technology to ensure the texture depth, the scattering effect of bubbles and the influence of negative pressure on the solid–liquid interface during the liquid phase assisted laser processing remove the oxide recast layer and burr on the surface of the sample, and improve the surface quality of the texture, thereby improving the surface friction behavior of the sample. This study promotes the development of surface texture laser processing technology and broadens the application field of 304 stainless steel.

Dual-Function Femtosecond Laser: β-TCP Structuring and AgNP Synthesis via Photoreduction with Azorean Green Tea for Enhanced Osteointegration and Antibacterial Properties.

β-Tricalcium phosphate (β-TCP) is a well-established biomaterial for bone regeneration, highly regarded for its biocompatibility and osteoconductivity. However, its clinical efficacy is often compromised by susceptibility to bacterial infections. In this study, we address this limitation by integrating femtosecond (fs)-laser processing with the concurrent synthesis of silver nanoparticles (AgNPs) mediated by Azorean green tea leaf extract (GTLE), which is known for its rich antioxidant and anti-inflammatory properties. The fs laser was employed to modify the surface of β-TCP scaffolds by varying scanning velocities, fluences, and patterns. The resulting patterns, formed at lower scanning velocities, display organized nanostructures, along with enhanced roughness and wettability, as characterized by Scanning Electron Microscopy (SEM), optical profilometry, and contact angle measurements. Concurrently, the femtosecond laser facilitated the photoreduction of silver ions in the presence of GTLE, enabling the efficient synthesis of small, spherical AgNPs, as confirmed by UV-vis spectroscopy, Transmission Electron Microscopy (TEM), and Fourier Transform Infrared Spectroscopy (FTIR). The resulting AgNP-embedded β-TCP scaffolds exhibited a significantly improved cell viability and elongation of human bone marrow mesenchymal stem cells (hBM-MSCs), alongside significant antibacterial activity against Staphylococcus aureus (S. aureus). This study underscores the transformative potential of combining femtosecond laser surface modification with GTLE-mediated AgNP synthesis, presenting a novel and effective strategy for enhancing the performance of β-TCP scaffolds in bone-tissue engineering.

An optical field regulation method for waterjet-guided laser: Reducing taper and improving deep-processing capability

Waterjet-guided laser (WGL) processing technology has the advantages of low thermal damage, no contact stress and ultra-fine processing. However, the energy distribution of the existing technology in the laminar flow water column is still characterized by Gaussian distribution, which leads to taper effect in the processing of thick plate materials and affects the deep-processing capability. To address these shortcomings, a novel waterjet laser-field regulation (WLR) method is proposed in this paper. Optical simulation and coupling experiments confirm the method's ability to modulate the energy within the waterjet into a circular distribution, which solves the problem of low power density near the surface of the waterjet. Waterjet-guided laser cutting experiments were conducted based on the WLR method, and the taper was significantly reduced compared to the conventional WGL. At a power of 12 W, the taper was reduced from 5.85° to 2.28°, a reduction of 61 %. In terms of processing depth, the WLR method cuts slightly lower groove depths with a low number of cuts, but as the number of cuts increases, the groove depth steadily increases and exceeds that of the conventional WGL. At 500 cuts with a laser power of 20 W, the groove depths obtained by the WLR method increased by 115 % compared to that of the conventional WGL. This study has important implications for the processing of thick materials by waterjet-guided laser.

Ultrasensitive strain sensor of dual parallel FPIs utilizing femtosecond laser processing and Vernier effect

This study proposes and develops a highly sensitive fiber optic strain sensor utilizing femtosecond laser processing and the Vernier effect. The sensor features two parallel Fabry-Pérot interferometers (FPI), with each FPI consisting of an air bubble and a tapered fiber optic cascade. FPI 2 serves as the sensing cavity, while FPI 1 acts as the reference cavity. The strain sensing capability of a single FPI 2 is measured at 6.67 p.m./με, while the parallel configuration of FPI 2 with FPI 1 achieves a sensitivity of 68.3 p.m./με, resulting in an amplification of 10.24. Furthermore, the proposed sensor demonstrates excellent repeatability, low-temperature cross-sensitivity, simple fabrication, and cost-effectiveness, making it a promising tool for strain measurement applications.

Characterizing the shaping, transmission, and amplification of near flat-top Gaussian beams through soft-edged apertures.

The near flat-top Gaussian beam, which finds significant applications in energy amplification, laser processing, nonlinear frequency transformation, and atmospheric turbulence studies, has received limited attention regarding its transverse mode field distribution characteristics during spatial transmission and amplification. In this study, we simulated the spatial transmission and amplification processes of the near flat-top Gaussian beam using the Collins diffraction equation and a traditional side-pumping gain model. To validate our simulations, we conducted experiments employing a gradual soft-edged aperture to produce a near flat-top Gaussian beam. Our findings revealed that during free transmission, the near flat-top Gaussian beam evolved into a Gaussian-like beam, and a secondary peak emerged when amplified by a conventional laser diode side-pumping amplifier. These results underscored the necessity of using an image transfer system to maintain the energy uniformity of the near flat-top Gaussian beam during amplification. Furthermore, we identified the optimal shaping parameter of the Gaussian beam with a soft-edged aperture to be approximately 2.3. By utilizing an image transfer system and a two-stage amplifier, we successfully amplified the beam energy post-shaping. Ultimately, we achieved a near flat-top Gaussian beam with an energy of 219.5 mJ and an energy root-mean-square (RMS) normalized deviation of 0.144, compared to the initial Gaussian beam, which had an energy of 52.3 mJ and an energy RMS normalized deviation of 1.434.

Review of high-precision femtosecond laser materials processing for fabricating microstructures: Effects of laser parameters on processing quality, ablation efficiency, and microhole shape

Femtosecond lasers are promising tools for achieving high-precision processing of thin materials without causing any thermal surface damage and bulk distortion. However, thermal damage can occur even with ultrashort laser pulses. This is because of high electron penetration depth and heat accumulation at high fluence and high repetition rate. Nanoparticle redeposition can be dramatically altered with variation in repetition rate. The symmetry of microholes and ablation efficiency vary with laser polarization. The laser wavelength affects the ablation efficiency and surface roughness. Therefore, understanding these laser–matter interactions that depend on the laser parameters is essential for high-precision laser processing. This article reviews laser–matter interactions in the 64FeNi alloy, as well as analytical models for designing the desired hole size and taper angles. This can help establish strategies for creating various high-precision microstructures using femtosecond lasers.

Size effects and optimization during laser directed energy deposition on high thermal conductivity copper alloys

High-copper alloy/nickel-based high-temperature alloy bimetallic structures are widely utilized in critical components, such as thrust chambers of liquid rocket engines, water cooling circuits for fusion reactor deflectors, and electromagnetic railguns. Among various methods for fabricating Cu/Ni bimetallic structures, laser directed energy deposition (LDED) is considered one of the most promising techniques for depositing nickel-based high-temperature alloys onto high-copper alloy surfaces. In the LDED fabrication process, substrates with uneven thicknesses are a common. The process is characterized by its multi-parameter, high-sensitivity, and non-equilibrium solidification characteristics. Consequently, variations in substrate size can significantly affect molten pool morphology and fabrication stability. This study examines the size effect of a single track of LDED Inconel 718 (In718) on a CuCr0.8 high-copper alloy substrate. The results indicate a pronounced size effect when using a high thermal conductivity CuCr0.8 substrate, particularly regarding substrate thickness. By reducing the thermal conductivity of the CuCr0.8 substrate, the size effect is mitigated, improving the process adaptability of LDED. These findings provide valuable data for the laser processing of surfaces with uneven thickness and high thermal conductivity. They are expected to support the fabrication of variable thrust liquid rocket engines and advance the field of interplanetary exploration.