Laser Processing Techniques Research Articles

Fabrication of bionic reed leaf superhydrophobic surface by laser processing

In the natural evolution, animals and plants have evolved many unique structures and properties. For example, butterfly wings appear to be colorful due to grating structures. Lotus leaves have super-hydrophobic property because of micro/ nano-structures. Nepenthes pitcher plants show slippery wettability by reason of the lubricant infused surfaces. Therefore, more and more researchers are trying to prepare unique structures which are similar to the surface of biological templates by different methods. Taking superhydrophobic surfaces as an example, there are many methods having been adopted to achieve superhydrophobic surfaces, such as etching, template method, UV lithography, electrostatic spinning, and nano-imprint technique. In recent years, laser processing technique has the advantages of high precision and arbitrary design, which shows great advantages in bionic manufacturing. For example, various kinds of micro/nano composites or structures have been successfully prepared by laser direct writing, two/four-beam interference, etc. However, these methods rely mainly on complex or sophisticated instruments, which take long time to prepare large-area superhydrophobic surfaces. Reed leaves show anisotropic superhydrophilicity property because of grating structures, which has applications in droplet transmission without loss and directional collection. Herein, we demonstrated the fabrication of bionic reed leaf by laser treatment of structured polydimethylsiloxane (PDMS) surface. Laser treatment of PDMS with micro-grating structures can induce the micro-nano structures and improve the surface roughness. To investigate the change of surface chemical composition, we carried out X-ray photoelectron spectroscopy (XPS) of PDMS before and after the laser treatment. After the laser treatment, the carbon content was decreased from 43.6% to 33.1%. The decrease in carbon content indicates the emission of carbon material during laser treatment, which is caused by the carbonization of the methyl group on the surface of the PDMS. At the same time, the oxygen content increased from 27.8% to 33.6% and the silicon content increased from 28.3% to 33.3%. To compare the surface morphologies changes of PDMS before and after laser treatment, we observed the surface morphology by confocal laser scanning microscopy (CLSM) and scanning electron microscope (SEM). The initial PDMS grating is about 100 μm wide, ~130 μm high and the structure surface is smooth. After laser treatment, it changes to about 200 μm wide, ~110 μm high and becomes much rougher surface. The variation in the width and height is mainly because that the laser treatment causes PDMS surface material to carbonize into rough structures. In order to evaluate the wettability changes of samples, the static water contact angle and dynamic water sliding angle measurement was carried out on the flat PDMS, the structured PDMS, and the laser-treated structured PDMS, respectively. The contact angle along the parallel direction was ∼155°, which is larger than that along the vertical direction (~150°). The sliding angle along the parallel direction was approximately 3°, which was smaller than the SA along the vertical direction (12°). This method provides a new idea for preparation of superhydrophobic surfaces with bionic structures by laser technology. The method is simple, convenient, and low cost, which may become a general method for preparing superhydrophobic surface.

Tunable charge states of nitrogen-vacancy centers in diamond for ultrafast quantum devices

A prerequisite condition for next-generation quantum sensing, communication, and computing is the precise modulation of the charge states of nitrogen-vacancy (NV) centers in diamond. We have achieved tuning of these centers in highly concentrated NV-diamonds using photons, phonons, and electrons. These NV-diamonds are synthesized employing a unique nanosecond laser processing technique which results in ultrafast melting and subsequent quenching of nitrogen-doped molten carbon films. Substitutional nitrogen atoms and vacancies are incorporated into diamond during rapid liquid-phase growth, where dopant concentrations can exceed thermodynamic solubility limits through solute trapping. This ultrafast synthesis technique generates fewer surface traps thereby forming ∼75% NV− centers at room-temperature, which are optically and magnetically distinct as compared to NV0 centers. We dramatically increase the NV− concentration in NV-diamonds by ∼53% with decreasing temperature from 300 to 80 K. With negative electrical biasing, the Fermi level in NV-diamond rises and crosses the NV0/- level, thereby promoting an exponential conversion of NV0 to NV− centers. We have also photonically enhanced the photoluminescence signal from NV− centers, thereby ascertaining the conversion of NV0 into NV−via absorption of electrons (excited by 532 nm photons) from the valence band in NV-diamond. These NV-centers in diamonds also reveal large excitation lifetime, which ultimately leads to ∼65% quantum efficiency at room-temperature. With these results, we believe that the precise tuning of charge states in these uniquely prepared highly concentrated NV-diamonds will lead to superior quantum devices.

Hybrid micro-optical elements by laser-based fabrication of Fresnel lenses on the end face of gradient index lenses.

Fresnel lenses are fabricated directly upon the end face of gradient index (GRIN) lenses by F2-laser machining at 157 nm wavelength. The employed laser processing technique combines a mask projection configuration at 25-x demagnification with a rotation of the structured lens. The ablation characteristics of the GRIN materials require very high pulse fluences with typical values above 7 J/cm2. Topography measurements on the Fresnel lenses reveal a good contour accuracy with residual deviations from the design profile well below 100 nm. Such hybrid optical elements, combining GRIN lenses with diffractive lenses in one element, can serve as the basis for high-performance micro-optical imaging systems with diameters up to 2 mm. Examples of possible applications include imaging sensors like proximity sensors or color-corrected microscope objectives with high numerical aperture for endoscopy applications.

Surface morphology of titanium alloy with monolayer microparticles under different single pulse laser energy

The surface morphology characteristics of titanium alloy under single pulse energy with local field enhancement effect were studied. The surface morphology of titanium alloy was observed by scanning electron microscope and local field enhancement theory was discussed by the FTDT simulation. The key difficulty of monolayer particles deposition was solved by production of a hydrophilic film and spin coating method. The formation mechanism of the surface morphology was discussed. Our results indicate the surface morphology is related to local field enhancement and the laser parameters including energy, size and distribution of laser spot. By using lower laser fluence than the ablation threshold of titanium alloy, laser cleaning can be obtained. When the microparticles-enhanced laser energy reaches the ablation threshold of titanium alloy surface, micropores whose size between 300 nm and 400 nm are easily obtained. The micropores distribution is related to the shape of laser spot. When the laser energy of laser spot exceeds the ablation threshold, microparticles help to control the shape of hole. The results show that particles can effectively influence the quality of laser processing, which is theory and practical significance on promoting laser processing technique in the application of particles on titanium alloy.

Review of Superelastic Differential Force Archwires for Producing Ideal Orthodontic Forces: an Advanced Technology Potentially Applicable to Orthognathic Surgery and Orthopedics.

Gentle and continuous loads are preferred for optimum orthodontic tooth movement. Nitinol, an alloy of nickel and titanium developed for the aerospace industry, found its first clinical applications in orthodontics because it has ideal load-deflection behavior. The purpose of this review is to elucidate the criteria for effective orthodontic mechanics relative to emerging Nitinol technology. The specialized materials with variable stiffness that were originally developed for orthodontics are increasingly attractive for in the temporomandibular joint, orthognathic surgery, and orthopedics. The evolution of orthodontic archwires is driven by a need to achieve low load-deflection characteristics and Nitinol is the alloy of choice. Scientific knowledge of the biological response to orthodontic forces continues to grow, but definitive guidance on optimal force levels for individual teeth is elusive. Finite element models (FEM) that take into account periodontal ligament (PDL) stresses indicate differential force archwires are needed to realize optimal treatment. However, previous wire fabrication methods, including welding of different materials and selective resistive heating, are limited by poor mechanical performance and spatial resolution. Recently, a novel laser processing technique was developed for precisely programing relative levels of stiffness in a single archwire. FEM was used to estimate the optimal force for each tooth by calculating the 3D bone-PDL surface area. There remains a general consensus that light and continuous forces are desirable for orthodontic treatment. New developments in archwire materials and technology have provided the orthodontist with a complete spectrum of load-deflection rates and differential force options to express these forces with maximized archwire economy. These technologies also appear to have application to orthopedic implant devices.

Creation of micro/nano surface structures on silver using collinear double femtosecond laser pulses with different pulse separation

Self-organized mound-like micro/nanoscale structures are reported for the first time on silver using a dual-pulse femtosecond laser surface processing technique. The dual-pulse laser processing technique reported in this paper uses femtosecond laser pulse pairs with a controlled temporal delay between the leading and trailing pulses. Using dual pulses at higher fluence values, mound-like micro/nanostructures have been created on silver samples for the first time. Formation of the self-organized microstructures is shown to be dependent on the time delay between the leading and trailing pulses. Mound-like microstructures do not develop on silver for overlapped pulses or using single-pulse femtosecond laser surface processing for the parameter space studied. Subsurface microstructure characterization of a single mound-like surface structure is analyzed by cross-sectional analysis using focused ion beam milling followed by scanning electron microscopy and energy dispersive X-ray spectroscopy.

Micro-structured optical fiber sensor for simultaneous measurement of temperature and refractive index

Abstract Through using micro-machining method for optical fiber sensor, a kind of miniature, compact and composite structural all-fiber sensor is presented. Based on manufacturing two micro-holes with certain distance in ordinary single-mode fiber Bragg grating (FBG) by excimer laser processing technique, we fabricate a dual Fabry–Perot-FBG (FP-FBG) composite fiber interferometric sensor, which can be used in simultaneous measurement for liquid’s refractive index (RI) and temperature change. Due to every micro-hole and the dual micro-holes in fiber acting as different Fabry–Perot (FP) cavities, this kind of sensor has not only different RI sensitivities but also different temperature sensitivities, which are corresponding to the wavelength shifts of the fine interference fringes and spectral envelope, respectively. The experimental results show that the spectral wavelength shift keep better linear response for temperature and RI change, so that we can select the higher temperature and RI sensitivities as well as the analyzed sensitivities of FBG to utilize them for constituting a sensitivity coefficients matrix. Finally, the variations of liquid’s temperature and RI are detected effectively, and the resolutions can reach to 0.1 °C and 1.0 × 10 - 5 RIU. These characteristics are what other single-type sensors don’t have, so that this kind of all-fiber dual FP-FBG composite fiber interferometric sensor can be used in extremely tiny liquid environment for measuring different physical quantities simultaneously.

Surface modification of TC4 Ti alloy by laser cladding with Ni-Ti-Nb powders

TC4 Ti alloy with the excellent properties can be applied to many fields, but the surface performance such as wear-resisting, fretting wear, contact corrosion etc.can't be met for many special demands. Laser cladding was applied on a TC4 Ti alloy to improve its properties. Mixed Ni,Ti and Nb powders were put onto the TC4 Ti alloy and subsequently treated by laser beam. The experimental results show that the surface hardness and wear resistance are significantly improved. The increase in wear resistance is predicted to be related to the "adaptive" wear mechanism of SMA.The microstructure and composition modifications in the surface layer were carefully investigated by using SEM, EDX and metallographic microscope. Experimental analyses show that the compositions of laser cladding coating are close to shape memory alloy of 44Ni-47Ti-9Nb,and differedt microstructure are rich with different elements. These experimental results are associated with laser processing techniques and alloy composition to some extent.

The optoelectronic properties of developed p–n junction on the textured silicon surface for improving the solar cell performance

Here, we report the development of the solar cell with a hybrid p-n junction based on poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) deposited on the textured Si surface. Texturing was accomplished by a laser processing technique, allowing the formation of nanopyramids on the Si surface, leading to ultralow reflectance. The PEDOT:PSS solution was deposited on the textured Si-wafer via a spin-coating technique. The evaluation of the I–V characteristics under illumination demonstrated an improvement of the short-circuit current density of the PEDOT:PSS/textured nanopyramid Si-substrate by 61% compared to that of the device based on the planar Si-substrate. The effect of the nanopyramid aspect ratio (height/diameter) of the textured Si-substrate on the optical absorption and reflection was studied to determine the optimum aspect ratio to achieve the maximum rate of the light entrapment. It was demonstrated that the increase of the aspect ratio leads to an enhancement of the short-circuit current and the filling factor. The hybrid device developed shows a promise for future applications in photovoltaic solar cell devices.

Investigating the effect of picosecond laser texturing on microstructure and biofunctionalization of titanium alloy

Laser processing technique has been an effective method to enhance the medical implant’s biocompatibility through forming specific textures on titanium alloy implant surface. In this paper, a 1064nm pulsed picosecond laser on TC4 titanium alloy implant samples was conducted to obtain optimal parameters for well-structured textures, controllable micro-grooves and improved osteoblast adhesion and proliferation. Picosecond laser technique is generally characterized by the high flexibility and advanced properties, which could make structural features including topography quality and detailed dimensions expediently improved and changed by adjusting laser processing parameters. To obtain the optimal laser processing parameters for desired microstructures, orthogonal experiments and related SEM, EDS and SPM analysis were conducted under various laser powers, repetition frequencies, scan speeds and scan numbers. Thus, the correlation between picosecond laser processing parameters and its corresponding microstructure feature of the micro-grooves was established. In addition, the immunofluorescence detection of cell actin cytoskeleton shows that structured textures can promote cell adhesion and play an important role in cell contact guidance.

Long Period Fiber Grating Inscribed in Hollow-Core Photonic Bandgap Fiber for Gas Pressure Sensing

In this paper, we have proposed and experimentally prepared an improved gas pressure sensing device. It is mainly constructed by a short hollow silica tube segment and a CO2-laser-induced long period grating in hollow-core photonic bandgap fiber (HC-PBF). To effectively enhance the interaction between light in the air-core of HC-PBF and external surroundings, thus to achieve the best possible gas pressure sensitivity, a microchannel is introduced in the middle of the hollow silica tube segment with the femtosecond laser processing technique. The corresponding gas pressure experiments demonstrate that the resonant wavelength of the LPFG shows a blue shift up to −1.3 nm/MPa. Moreover, the temperature response sensitivity of this sensor is as low as 5.3 pm/°C and enable it possible as a temperature-insensitive gas pressure measure apparatus.

Sharp improvement of flashover strength from composite micro-textured surfaces

A composite micro-textured surface structure is proposed and demonstrated to enhance the surface flashover strength of polymer insulators used in vacuum. The structure is fabricated in two stages, with periodic triangular grooves of approximately 210 μm in width formed in the first stage and micro-holes of approximately 2 μm coated on the inner surface of grooves in the second. The aim is to exploit the synergistic effects between the grooves and micro-holes to suppress the secondary electron yield to obtain a better flashover performance. To acquire insulators with the composite micro-textured surface, the CO2 laser processing technique is applied to treat the surface of the PMMA insulators. The test results show that the flashover voltages of the insulators with the two-stage fabricated structure increase by 150% compared with the untreated samples in the best state. Compared with the traditional macro-groove structures on insulators, the proposed composite micro-textured insulators exhibit a better surface flashover performance.

Lasers Improve Display Glass Cutting

Non‐contact glass cutting by laser offers an attractive alternative to mechanical methods in display fabrication. There are several laser technologies and processing techniques in actual use, each with its own characteristics and advantages.

A Review on Laser Processing in Electronic and MEMS Packaging

The packaging of electronic and microelectromechanical systems (MEMS) devices is an important part of the overall manufacturing process as it ensures mechanical robustness as well as required electrical/electromechanical functionalities. The packaging integration process involves the selection of packaging materials and technology, process design, fabrication, and testing. As the demand of functionalities of an electronic or MEMS device is increasing every passing year, chip size is getting larger and is occupying the majority of space within a package. This requires innovative packaging technologies so that integration can be done with less thermal/mechanical effect on the nearby components. Laser processing technologies for electronic and MEMS packaging have potential to obviate some of the difficulties associated with traditional packaging technologies and can become an attractive alternative for small-scale integration of components. As laser processing involves very fast localized and heating and cooling, the laser can be focused at micrometer scale to perform various packaging processes such as dicing, joining, and patterning at the microscale with minimal or no thermal effect on surrounding material or structure. As such, various laser processing technologies are currently being explored by researchers and also being utilized by electronic and MEMS packaging industries. This paper reviews the current and future trend of electronic and MEMS packaging and their manufacturing processes. Emphasis is given to the laser processing techniques that have the potential to revolutionize the future manufacturing of electronic and MEMS packages.

Improvement of crystal identification performance for a four-layer DOI detector composed of crystals segmented by laser processing

We have developed a four-layer depth of interaction (DOI) detector with single-side photon readout, in which segmented crystals with the patterned reflector insertion are separately identified by the Anger-type calculation. Optical conditions between segmented crystals, where there is no reflector, affect crystal identification ability. Our objective of this work was to improve crystal identification performance of the four-layer DOI detector that uses crystals segmented with a recently developed laser processing technique to include laser processed boundaries (LPBs). The detector consisted of 2×2×4mm3 LYSO crystals and a 4×4 array multianode photomultiplier tube (PMT) with 4.5 mm anode pitch. The 2D position map of the detector was calculated by the Anger calculation method. At first, influence of optical condition on crystal identification was evaluated for a one-layer detector consisting of a 2×2 crystal array with three different optical conditions between the crystals: crystals stuck together using room temperature vulcanized (RTV) rubber, crystals with air coupling and segmented crystals with LPBs. The crystal array with LPBs gave the shortest distance between crystal responses in the 2D position map compared with the crystal array coupled with RTV rubber or air due to the great amount of cross-talk between segmented crystals with LPBs. These results were used to find optical conditions offering the optimum distance between crystal responses in the 2D position map for the four-layer DOI detector. Crystal identification performance for the four-layer DOI detector consisting of an 8×8 array of crystals segmented with LPBs was examined and it was not acceptable for the crystals in the first layer. The crystal identification was improved for the first layer by changing the optical conditions between all 2×2 crystal arrays of the first layer to RTV coupling. More improvement was observed by combining different optical conditions between all crystals of the first layer and some crystals of the second and the third layers of the segmented array.

Laser Processing of Low Optical Reflection Micro/Nano-patterned Si Substrates for SERS

ABSTRACTLight collection efficiency and specific molecular detection are crucial factors for the performance of bio-chemical molecule sensors. In this paper, the low optical-reflection silicon (Si) substrates which combine reduced optical reflectivity by light trapping effect and high Raman enhancement ability of gold nanoparticles (Au-NPs) coated textured Si substrates are investigated for surface-enhanced Raman scattering (SERS). A fast, single-step and highly controllable nanosecond (ns) laser processing technique is employed to fabricate textured Si substrates under ambient conditions. Parallel arrays of micro-pyramids are fabricated on Si surface by direct laser writing two-dimensional structures. SEM micrographs clearly show well-ordered surface features in the form of micro-pyramid shape with well-defined sharp tips on the laser processed Si substrates. The aggregation of Si micro/nanoparticles on Si surface forms nanocavities and nanogaps and further enhances the surface roughness in order to minimize the optical reflection. The low optical reflection Si substrates exhibit optical reflection below 15% over a broad wavelength range from 300 nm to 1200 nm. The textured Si substrates with high signal reproducibility are successfully applied as SERS substrates to detect a very small concentration of Rhodamine B molecules with an average enhancement factor of the order of ∼107. The low optical reflection and SERS signal amplification are also altered by the variation of laser pulse energy resulting into low optical reflection and high SERS signal intensity over the entire laser-patterned area. The effect of surface roughness on water contact angle was studied after the modification with Polydimethylsiloxane (PDMS), the surfaces show perfect superhydrophobicity with almost no water adhesion. This approach provides a novel high-speed and cost-effective method for fabricating SERS substrate with micro/nano-scale surfaces roughness and low optical reflection for high Raman signal enhancement.

Handheld Electrical Impedance Myography Probe for Assessing Carpal Tunnel Syndrome.

Electrical impedance myography (EIM) is a novel, noninvasive, and painless technique for quantitatively assessing muscle health as well as disease status and progression. The preparatory work for commercial adhesive electrodes used in previous EIM measurements is tedious, as the electrodes need to be cut, repeatedly applied, and removed. Moreover, the electrode distances need to be measured many times. To overcome these problems, we developed a convenient and practical handheld EIM probe for assessing carpal tunnel syndrome (CTS) in the small hand muscles. To reduce the electrode-skin contact impedance (ESCI), the micropillared and microholed stainless steel electrodes (SSEs) contained in the probe were fabricated using a laser processing technique. When covered with saline, these electrodes showed lower ESCIs than a smooth SSE and Ag/AgCl electrode. The probe was shown to have excellent test-retest reproducibility in both healthy subjects and CTS patients, with intraclass correlation coefficients exceeding 0.975. The reactance and phase values of the abductor pollicis brevis (affected muscle) for CTS patients were consistently lower than those for healthy subjects, with a 50-kHz difference of 37.1% (p<0.001) and 31.0% (p<0.001), respectively. Further, no significant differences were detected in the case of the abductor digiti minimi (unaffected muscle). These results indicate that EIM has considerable potential for CTS assessment and hence merits further investigation.

Toward On-Chip Unidirectional and Single-Mode Polymer Microlaser

Optical microcavities have been paid enormous attentions as a basic integrated element in photonic devices including micromodulators, microfilters, and microsensors. In particular, the microcavities that can produce unidirectional and single-mode lasing emissions are greatly demanded to meet the challenge of integrating high-efficiency and high-sensitivity optical functional systems. Herein, a three-dimensional polymer microlaser composed of stacked circular-ring-shaped and spiral-ring-shaped microcavities is fabricated directly on a narrow bandpass filter substrate by the femtosecond laser processing technique. The on-chip polymer microlaser provides a room-temperature, low-threshold, unidirectional, and single-mode laser output, resulting from the coupling between the two stacked microcavities. The fabrication of the on-chip low-threshold polymer microlaser opens up a possibility toward the integration of a variety of polymer microcavities for organic optoelectronic devices.

Shield gas induced cracks during nanosecond-pulsed laser irradiation of Zr-based metallic glass

Laser processing techniques have been given increasing attentions in the field of metallic glasses (MGs). In this work, effects of two kinds of shield gases, nitrogen and argon, on nanosecond-pulsed laser irradiation of Zr-based MG were comparatively investigated. Results showed that compared to argon gas, nitrogen gas remarkably promoted the formation of cracks during laser irradiation. Furthermore, crack formation in nitrogen gas was enhanced by increasing the peak laser power intensity or decreasing the laser scanning speed. X-ray diffraction and micro-Raman spectroscopy indicated that the reason for enhanced cracks in nitrogen gas was the formation of ZrN.

Experimental validation of a one-dimensional model for monolithic shape memory alloys with multiple pseudoelastic plateaus

A one-dimensional approach to simulate the mechanical properties of multifunctional pseudoelastic NiTi shape memory alloy has been developed. A novel laser processing technique was applied to a NiTi wire to locally alter the pseudoelastic properties, giving the wire different regions with unique material properties. An innovative analytical expression was developed and validated experimentally. The simulated material responses closely predicted the experimentally measured laser-processed shape memory wires.