Superhydrophobic surfaces are the most commonly used functional surfaces. Femtosecond laser processing technology has emerged as a useful instrument for producing micro- and nanoscale structures on superhydrophobic surfaces because of its extremely high processing accuracy and highly controlled features. The substrate materials used in this work are AH36 steel plates. By varying the laser processing parameters, the microstructure shapes of steel plate surface are produced. After processing, the samples were allowed to rest in air for 30 days before characterizing their hydrophobicity. The optical and scanning electron microscopy were used to analyze its morphology, and the contact angles were measured. The study demonstrated that the surface roughness, microstructure, and hydrophobicity of AH36 steel plate samples vary with laser parameters. As a result, the AH36 steel plate exhibits the creation of a superhydrophobic surface when the contact angle reaches 151.2°, with a scanning interval of 100 μm between two lines, scanning speed of 10 mm/s, and an energy density of 3.67 J/cm². This is an important result for promoting femtosecond laser in preparing hydrophobic structures on marine metal surface.
The High Temperature Co-fired Ceramic (HTCC) substrate boasts advantages such as high structural strength, high thermal conductivity, and good chemical stability, thus showing broad application prospects in high-power microcircuits. As the circuit board material, it is necessary to use mechanical or laser drilling on the raw porcelain, and the aperture of through hole and position accuracy directly affect the yield and final electrical properties of the substrate. In recent years, laser processing technology has the advantages of high precision, high efficiency, stable performance and no contact, which increasingly become one of the most critical processes of multi-layer ceramic packaging technology. In this paper, the ultraviolet (UV) picosecond laser with pulse width of 15 ps was used for HTCC drilling with thickness of 0.14mm. The laser has a maximum power of 30W at a repetition rate of 600 kHz, a spot size of 20 μm after focusing, and a wavelength of 355nm. By optimizing the process parameters, including laser power, frequency, scanning speed, and repetitions, a minimum through-hole with diameter of 100 μm, with an accuracy of ±5 μm for entrance and exit holes were achieved. Under optical microscope, roundness, taper, and Heat-Affected Zone (HAZ) of hole under different conditions were obtained and analyzed. These results prove that ultra-fast laser processing can be an efficient HTCC drilling technique.
Owing to the exceptional physical and mechanical properties, alumina ceramics are widely applied in industrial manufacturing, where laser technology is pivotal for achieving high-precision cutting. This study investigates the laser ablation of alumina ceramics using fiber lasers, complemented by simulation to optimize processing parameters. The laser has a maximum average power of 150 W with a fiber core diameter of 25 μm. By varying laser power, frequency, and scanning speed, at an average power of 90W and a frequency of 400 Hz, the ablation efficiency and surface quality are enhanced while minimizing heat-affected zone of 50 μm. Simulation results accurately predict temperature distribution and material removal, aligning well with experimental data, thus advancing the precise machining of hard ceramics.
At present, laser cutting has emerged as a new technology in the field of glass cutting to achieve a good quality and high efficiency, that is believed to have a very broad application prospect. In this report, the glass cutting by picosecond laser with a high peak power and a long focal-depth Bessel beam was studied. The maximum power of laser is chosen to be 50 W with a spot size of 2 mm, pulse width of 10 ps, and wavelength of 1064 nm. The frequency is adjustable in the range of 50 KHz to 200 KHz. The factors affecting the cutting roughness was analyzed, including the focus position, speed, and power. Meanwhile, the glass is split by a carbon dioxide laser with the wavelength of 10.6 μm and maximum power is 100 W, which breaks due to internal stress induced by heating. By adjusting the speed, power and focusing position, the good processing parameters for the ultra-white glass with thickness of 4 mm were found. High quality cutting with minimum edge breakage less than 3 μm is confirmed by microscope. Moreover, nonstandard-shaped cutting and straight line cutting with a high speed of 300 mm/s have also achieved in this work. All results demonstrates that ultra-fast laser is a promising tool for glass cutting.
As the third generation of photovoltaic cell technology, the Perovskite Solar Cells (PSCs) have strong theoretical advantages compared with discrystalline silicon and thin film cells because of their material characteristics. In the formation of the series structure of perovskite cells, different film layers need to be marked at different positions. The scribing of functional layers can be done by mask plate, chemical etching, mechanical or laser scribing. Laser scribing can produce finer scribing areas. At present, laser scribing has gradually replaced other scribing methods and become the main scribing methods. In this paper, laser scribing for the realization of all the P1, P2, and P3 scribes are reported by optical fiber femtosecond laser with output wavelengths of 532 nm, and pulse width is adjustable at 300 fs. The better processing parameters are found for the scribing speed of 2000 mm/s, and the laser power of 1.8 W for the P1 scribe. High precision scribing with slit width less than 10 μm is obtained by optimizing scribing speed and laser power. All the results indicate that laser scribing would play an important role in achieving high performance PSCs modules in which the interconnects.
In this work, the effects of direct femtosecond laser nanostructuring on monocrystalline silicon (Si) wafer immersed in liquid environment were studied. Ultrashort laser exposure induced nonequilibrium states in materials triggers the morphology self- organization driven by excited electromagnetic and hydrodynamic processes, which ultimately give rise to the formation of regular nanogratings with different periodicity (Λ1=250 nm to 300 nm, Λ2=70±10 nm) and randomly arranged spike structures. The type of the nanotextures can be controlled by varying the laser fluence and polarization distribution of the incident laser beam studied for the cases of linearly/circularly polarized Gaussian laser beams as well as azimuthally polarized cylindrical vector beam. Through laser-induced interface chemical reactions stimulated by adding the appropriate salt/acid/molecular precursors in the process of liquid-phase Si texturing, it becomes possible to functionalize the obtained nanotextures with mono- and multi-metallic nanoparticels and/or photoluminescent chemosensing molecular probes. Adjusting laser processing parameters and component functionalizing solutions has providing a flexible approach for large-scale manufacturing that can be realized for diverse applications such as light harvesting, chemosensing, optical detection, heterogeneous catalysis and microfluidics.
We demonstrate comparatively the laser performance of 970 nm laser diode (LD) side-pumped Er:YSGG crystals with a length of 85 mm and diameters of 2, 3, and 4 mm. The maximum average powers of 25.18, 25.74, and 20.41 W are achieved at 150 Hz and 200 μs, corresponding to the slope efficiencies of 30.01%, 31.47%, and 24.38%, respectively. The experimental results show that the Er:YSGG crystal rod with a diameter of 2 mm has no obvious advantage in laser output at low frequency and low pump power because the gain volume is small and the pump power cannot be fully absorbed, resulting in the gain saturation phenomenon. However, it exhibits the best laser output under high repetition rate and high pump power. The average power of 16.47 W obtained at 500 Hz is still not saturated. The beam quality factors M2 in the x and y direction are determined to be 3.15/3.12, respectively, which is significantly better than those of the rods with diameters of 3 and 4 mm. All the results indicate that the crystal rod with a smaller diameter has better thermal management due to its larger specific surface area and better cooling ability, which is conducive to improving laser performance under the high repetition rate and high pump power operation.
Laser shock peening as one kind of surface technique is used to enhance the mechanical property of metals, like aluminum alloy, stainless steel, and titanium alloy. The Ti6Al4V alloy specimens are processed with laser shock peening technology by nanosecond laser with a square laser spot. The hardness near-surface region and residual stress distribution in the top layer of Ti6Al4V alloy specimen are measured by Vickers hardness tester and hole drilling tester. The results show that the shock wave formed by laser shock peening can induce compressive residual stress in the top layer of Ti6Al4V alloy, which is beneficial for the improvement of fatigue life of Ti6Al4V alloy when it is used in aviation. The hardness of the near-surface region increases slightly in this research.
Laser shock peening is a new and important surface treatment technique that can enhance the mechanical properties of metal materials. Normally, the nanosecond laser with pulse-width between 5 ns and 20 ns is used to induce a high-pressure shock wave that can generate plastic deformation in the top layer of metals. The femtosecond laser shock peening in the air has been studied recently, which can induce higher pressure shock wave than that of traditional nanosecond laser shock peening in a very short time. The NiTi alloy is processed by femtosecond laser shock peening, then a nanoindentation device is used to measure its surface hardness and residual stress. The hardness results of NiTi alloy before and after treatment show that the femtosecond laser shock peening can increase the hardness of NiTi alloy, which also shows that the femtosecond laser can be used to perform laser shock peening on NiTi alloy without coating.
High strength steel has been used in the aviation industry and automotive body structural applications to reduce its mass through a reduction in thickness. Therefore, it is very important to enhance its mechanical property, such as microhardness. In the present research, the high strength steel samples were treated by laser shock peening (LSP) with different laser pulse energy and laser pulse width. The microhardness and residual stress were measured to compare the difference between laser energy of 3 J with 10 ns and 5 J with 20 ns. The results in the study show that the surface LSP treatment can increase the microhardness and the compressive residual stress can be found when the samples were tested by hole drilling testing.
In this study, we use a hybrid mode-locked external cavity diode laser with subsequent amplification and pulse compression. The system provides laser pulses of 440 fs width (assuming a sech² pulse shape) and 160 mW average output power at a repetition rate of 383.1 MHz. The laser oscillator consists of a double quantum well laser diode with a gain segment of 1080 μm length and an absorber element of 80 μm lengths. The chip’s back facet is covered with a high reflective coating, the front facet with an anti-reflective coating. The resonator itself is operated in a collimated geometry and folded by two dielectric mirrors. The used output coupler provides a transmission of 20 percent, which is coupled into a tapered amplifier. Two Faraday isolators are used to decouple the laser and the amplifier from any back reflections. Subsequently, the pulses are compressed using a single pass Martinez type pulse compressor. Experiments on Two-Photon Polymerization were conducted on a conventional setup consisting of a 2D galvo-scanner system with an attached microscope objective. The oil immersion objective (NA =1.4) focusses the light pulses through a cover glass into a droplet of the photosensitive material. Process monitoring can be achieved by observing the image on a camera placed behind a semi-transparent mirror in front of the galvo-scanner. Using this experimental setup, test structures that consist of free-hanging lines supported by cuboids were produced. In addition, a procedure for automated linewidth measurements is outlined and used for analyzation of the generated structures. This work shows that mode-locked diode lasers can be used for the fabrication of microstructures by Two-Photon Polymerization. Typically used Ti:Sapphire or fiber lasers can be replaced by mode-locked diode lasers for Two-Photon- Polymerization. This allows for much cheaper Two-Photon-Polymerization systems and therefore, may open this field for more application-based research groups.
The experiment study presents the influence of femtosecond laser shock peening (FsLSP) without a protective layer in the air on the surface hardness and surface mechanical property of NiTi shape memory alloy. Femtosecond laser shock peening is a new possibility of direct laser ablation without any protective layer under atmospheric conditions, which can produce intense shock waves with low pulse energy in the air. The average surface roughness values of the NiTi alloy samples were measured, because the surface roughness may affect its friction resistance. The results showed that the surface roughness of NiTi increased after femtosecond laser shock peening treatment. In comparison with the initial state, the coefficient of friction decreased and surface microhardness increased after femtosecond laser shock peening treatment with different FsLSP parameters. This improvement of wear properties may be attributed to the enhancement of surface microhardness and surface titanium oxide layer induced by the shock wave and laser ablation during FsLSP treatment.
Most common colors in our world as we see them, for example, in crystals, pigments, metals and salt solutions are the result from light scattering properties of electrons in atoms and molecules. Nevertheless, colors can also result from light interference effects, which are of great importance in the life of organisms. The structural colors of living organisms, e.g., the wings of some birds, insects and butteries, are often more intense and almost angle-independent. Understanding this specific color formation is of great interest for biology and for engineered materials with a broad range of biomimetic real world applications due to forgoing of toxic dyes and pigments. Therefore, the generation of artificial color formation with lithographic methods offers many advantages not available in coated multilayer systems because it avoids multiple complex fabrication steps.
In the present work, we report an effortless fabrication method to generate structural coloration based on microand nano-structures using 3d-laser writing technique. The uniform micro- and nano-structures were produced in a thin polymer film with an refractive index of 1.51. The single structures are aligned in an array to create a blue color field. The identification of the influence of the structures on the artificial color formation was performed using scanning electron microscopy. The optical properties of the blue color was analyzed via an angle-resolved spectrometer.
To respond to current demands of nano- and microtechnologies, e.g., miniaturization and integration, different bottom-up strategies have been developed. These strategies are based on picking, placing, and assembly of multiple components to produce microsystems with desired features. This paper covers the fabrication of arbitrary-shaped microcomponents by two-photon polymerization and the trapping, moving, and aligning of these structures by the use of a holographic optical tweezer. The main focus is on the assembly technique based on a cantilever microsnap-fit. More precisely, mechanical properties are characterized by optical forces and a suitable geometry of the snap-fit is designed. As a result of these investigations, a fast and simple assembly technique is developed. Furthermore, disassembly is provided by an optimized design. These findings suggest that the microsnap-fit is suitable for the assembly of miniaturized systems and could broaden the application opportunities of bottom-up strategies.
A promising fabrication method for graphene is the reduction of graphene oxide (GO), this can be achieved photochemically by laser irradiation. In this study, we examine the results of latter method by a femtosecond fiber laser (1030 nm, 280 fs). The chemical properties of the irradiated areas were analyzed by Raman and X-ray photoelectron spectroscopy (XPS) and electrical properties were evaluated using sheet resistance measurements. We found that, within a wide range of fluences (8.5 mJ/cm2 to 57.8 mJ/cm2) at high overlapping rates (>99.45 %), photochemical oxygen reduction can be achieved. However, hybridization transition of sp3 to sp2 graphene-like structures only takes place at upper fluences of the mentioned range.
Ultrashort pulse laser ablation has become an important tool for material processing. Adding liquids to the process can be beneficial for a reduced debris and heat affected zone width. Another application is the production of ligand-free nanoparticles. By measuring the ablation rate of iron for femtosecond pulsed laser ablation in different solvents and solvent-mixtures, the influence of the solvent properties on the ablation process is studied. The ablation efficiency is quantified by measuring the ablation rate in dependency of the fluence from 0.05 J/cm2 up to 5 J/cm2 in water-ethanol and water-acetone mixtures which are varied in 25 % steps. The ablation rate is significantly influenced by the solvent-mixtures.
Laser pulses in the picosecond and femtosecond regime enable nearly non-thermal material processing where heat effects like molten pools and thermal tensions are often significantly reduced. However, a residual amount of laser energy transforms into heat. As a consequence cumulative multiple shot processing leads to heat accumulation and subsequently lower manufacturing accuracy. To increase the processing throughput without losing quality, it is important to optimize the laser pulse properties and the ablation strategy to further reduce thermal effects. Due to a low heat capacity in small structures, it is necessary to consider the substrate dimensions while performing micro- and nanoprocessing. In contrast to bulk material ablation, the heat dissipation is confined by the small heat capacity of microstructures. Especially for complex structures, it is time-consuming to find efficient processing parameters manually. For this reason, an in-situ evaluation system based on electrical resistivity measurements for on-line control of the ablation process was developed to optimize the laser parameters. In the work presented, the efficiency of 35 femtosecond pulsed laser ablation was evaluated on copper structures in the micrometer range. Furthermore, these results have been compared and evaluated with surface profiles measured by white-light interferometry.
This paper reports ex-situ preparation of conductive polymer/single-walled carbon nanotubes (SWNTs) nanocomposites by adding high conductive SWNTs to the polymer matrix. Sonication methods were used to disperse the SWNTs in the polymer. The conductivity of the nanocomposites is tuned by increasing the concentration of SWNTs. Furthermore, we present two-photon polymerization (2PP) method to fabricate structures on the basis of conductive photosensitive composites. The conductive structures were successfully generated by means of 2PP effect induced by a femtosecond laser.
Pumping and mixing of small volumes of liquid samples are basic processes in microfluidic applications. Among the number of different principles for active transportation of the fluids microrotors have been investigated from the beginning. The main challenge in microrotors, however, has been the driving principle. In this work a new approach for a very simple magnetic driving principle has been realized. More precisely, we take advantage of optical grippers to fabricate various microrotors and introduce an optical force method to characterize the fluid flow generated by rotating the structures through magnetic actuation. The microrotors are built of silica and magnetic microspheres which are initially coated with Streptavidin or Biotin molecules. Holographic optical tweezers (HOT) are used to trap, to position, and to assemble the microspheres with the chemical interaction of the biomolecules leading to a stable binding. Using this technique, complex designs of microrotors can be realized. The magnetic response of the magnetic microspheres enables the rotation and control of the structures through an external magnetic field. The generated fluid flow around the microrotor is measured optically by inserting a probe particle next to the rotor. While the probe particle is trapped by optical forces the flow force leads to a displacement of the particle from the trapping position. This displacement is directly related to the flow velocity and can be measured and calibrated. Variations of the microrotor design and rotating speed lead to characteristic flow fields.
The present work reveals the structural and magnetic properties of iron oxide (FexOy) nanoparticles (NPs) prepared by femtosecond laser ablation. The FexOy-NPs were produced in solutions consisting of different ratios of water and acetone. Laser ablation in water yields agglomerates and that in acetone yields chain structures whereas that in water/acetone show a mixture of both. We observe significant fabrication dependent properties such as different crystallinities and magnetic behaviors. The structural characterization shows a change from iron (Fe) to a FexOy state of the NPs which depends on the solution composition. Furthermore, transmission electron microscopy measurements exhibit a broad particle size distribution in all samples but with significant differences in the mean sizes. Using magnetic measurements we show that nanoparticles fabricated in pure acetone have lower coercive fields which come along with a smaller mean particle size and therefore increasing superparamagnetic behavior.
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