Direct Laser Ablation Research Articles

Refractive twisted microaxicons.

Complex-shaped light fields with specially designed intensity, phase, and polarization distributions are highly demanded for various applications including optical tweezers, laser material processing, and lithography. Here, we propose a novel (to the best of our knowledge) optical element formed by the twisting of a conic surface, a twisted microaxicon, allowing us to controllably generate high-quality spiral-shaped intensity patterns. Performance of the proposed element was analyzed both analytically and numerically using ray approximation and the rigorous finite difference time domain (FDTD) solution of Maxwell's equation. The main geometric parameters, an apex cone angle and a degree of twisting, were considered to control and optimize the generated spiral-shaped intensity patterns. The three-dimensional structure of such a microaxicon cannot be described by an unambiguous height function; therefore, it has no diffraction analogue in the form of a thin optical element. Such an element can be produced via direct laser ablation of transparent targets with structured laser beams or direct laser writing via two-photon photopolymerization and can be used in various micro- and nano-optical applications.

Lithography and Etching‐Free Microfabrication of Silicon Carbide on Insulator Using Direct UV Laser Ablation

Silicon carbide (SiC)‐based microsystems are promising alternatives for silicon‐based counterparts in a wide range of applications aiming at conditions of high temperature, high corrosion, and extreme vibration/shock. However, its high resistance to chemical substances makes the fabrication of SiC particularly challenging and less cost‐effective. To date, most SiC micromachining processes require time‐consuming and high‐cost SiC dry‐etching steps followed by metal wet etching, which slows down the prototyping and characterization process of SiC devices. This work presents a lithography and etching‐free microfabrication for 3C‐SiC on insulator‐based microelectromechanical systems (MEMS) devices. In particular, a direct laser ablation technique to replace the conventional lithography and etching processes to form functional SiC devices from 3C‐SiC‐on‐glass wafers is used. Utilizing a single line‐cutting mode, both metal contact shapes and SiC microstructures can be patterned simultaneously with a remarkably fast speed of over 20 cm s−1. As a proof of concept, several SiC microdevices, including temperature sensors, strain sensors, and microheaters, are demonstrated, showing the potential of the proposed technique for rapid and reliable prototyping of SiC‐based MEMS.

Microfabrication of UV-transparent fluoropolymer using high-repetition femtosecond oscillator

Surface microfabrication of a UV-transparent fluoropolymer (CYTOP) was achieved using direct laser ablation with a femtosecond (fs) oscillator. The commercially available CYTOP is highly transparent and has a low refractive index comparable to that of water. Therefore, this polymer is a candidate biochip material for application in the field of tissue engineering. We have previously developed techniques for microfabrication of CYTOP using nanosecond and amplified fs laser ablation, both followed by wet etching and annealing. However, these techniques were not suitable for some industrial applications due to the generation of debris and cracks around the ablated areas, which called for prolonged etching during the fabrication process. To overcome these problems, we have attempted to directly ablate the surface of a CYTOP substrate using a high-repetition fs oscillator and compared the results with fabrication using an amplified fs laser at a low repetition rate. Consequently, ablation with the fs oscillator resulted in high-quality surface microfabrication of the CYTOP substrate. The fundamental characteristics of CYTOP microfabrication using the fs oscillator were investigated. We also demonstrate the fabrication of a transmission diffraction grating on CYTOP using the fs oscillator, and measure the diffraction efficiency of the grating using a 632 nm He–Ne laser.

Rapid determination of lead isotopes in water by coupling DGT passive samplers and MC-ICP-MS laser ablation

We have developed a method for measuring Pb-isotope compositions in natural water, based on coupling a commercially available chelex-100 DGT passive sampler with direct laser-ablation MC-ICP-MS on DGT resin.

Laser-assisted surface processing for functionalization of polymers on micro- and nano-scale

Rapid manufacturing of functionalized polymers enable a cost-efficient method for many applications in the biological, and medical sector. Laser structuring techniques differ for fast fabrication processes of thermoplastics. Here we report on direct UV laser ablation of polystyrene and polydimethylsiloxane to control wettability and bio-compatibility. For this purpose contact angle measurements and L929 cell growth experiments were performed as function of laser and process parameters. This work also describes the potential of laser-assisted hot embossing which has been introduced to replicate pre-fabricated micro- and nano-sized structures onto polymers proving it to be a cost-efficient and flexible method for surface functionalization. Therefore, pre-fabricated laser-induced periodic surface structures have been manufactured as mould inserts using ultrafast laser radiation near the ablation threshold. These mould inserts can also be made of nickel, silicon or glass proving laser-assisted hot embossing to be a versatile tool for the functionalization of thermoplastics and meet the requirements for modern manufacturing with regard to quality and production flexibility.

High-performance oil-water separation polytetrafluoroethylene membranes prepared by picosecond laser direct ablation and drilling

The membranes with special surface wettability have attracted considerable attention, especially in the practical applications of oil-water separation. Here, we presented a simple and rapid method of picosecond (ps) laser direct ablation and then drilling to fabricate high-performance oil-water separation polytetrafluoroethylene (PTFE) membrane. It was found that the as-prepared rough PTFE membranes had ca. 0° contact angle (CA) of oil in air and above 150° CAs of water in air or oil, respectively, exhibiting superoleophilicity and under-oil superhydrophobicity. The micropore size of the membranes was less than ca. 180 μm, the corresponding separation efficiencies were over 99.0% for different oil-water mixtures due to the special and rough surface microstructures. Importantly, the separation efficiencies and fluxes of the as-prepared membranes showed no obvious change with suffering heavy erosion or 40 separation cycles, indicating that the membranes had excellent stability and applicability. Additionally, the effect of the special and rough surface on oil-water separation performance was investigated. This work provides a new pathway for the rapid fabrication of high-performance separation membranes.

(Invited) Tuning Electrochemical Performance of Lithium-Ion Cells By Introducing Laser-Generated Electrode Architectures

Laser technology in lithium-ion battery (LIB) manufacturing could enable rapid manufacturing, high reliability, and a reduction of production costs. Laser cutting and welding processes for batteries already reached a high industrial readiness level. A new approach which is assigned to laser micro-structuring of battery materials has a huge impact on battery performance and operational lifetime of lithium-ion cells and an up-scaling for industrial production is currently investigated. So far, different types of laser structuring were used on metallic current collectors, separators, and thin or thick film composite electrodes. For thin metallic current collector foils, at anode and cathode sides, self-organized structuring by laser-induced periodical surface structures were successfully applied for improving electrode film adhesion. Direct laser ablation was applied for the generation of capillary structures, which was found to be most powerful in order to transform electrode and separator surfaces to superwicking. Thick film composite electrodes in lithium-ion cells are complex multi-material systems with defined material components, grain sizes, porosities, and pore size distributions in the micrometer and sub-micron range. The development of laser generated electrode architectures became a promising approach to overcome limitations in lithium-ion diffusion kinetics, high inter-electrode ohmic resistances, and mechanical stresses due to high volume changes during battery operation. It was shown, that structure sizes down to 10-30 µm and high aspect ratios enable advanced electrode architectures with huge benefits regarding capacity retention and cell life-time for high power operations during charging/discharging. For laser structured electrodes, the overall impedance was reduced and the diffusion kinetics could be enhanced which was proven by galvanostatic intermittent titration technique, cyclic voltammetry, and electrochemical impedance spectroscopy. Furthermore, the new electrode architecture provides new lithium-ion diffusion pathways, which could be indirectly proven by post-mortem analysis of entire electrodes by laser-induced breakdown spectroscopy (LIBS). It is evident that the increased active surface area provided by laser generated electrode architectures act as an attractor for lithium-ions which finally is responsible for the boost in battery performances. By increasing the cathode film thickness to values significantly larger than 150 μm an increase of the specific capacity or energy density at cell level was achieved. While the energy per area increases with the cathode layer thickness, the power density will in general decrease due to an increasing diffusion overpotential. In addition, the mechanical integrity of the films will decrease with increasing layer thickness and the migration of binders to the electrode surface will occur through altered drying conditions. The mechanical degradation of the cells due to the volume change inherent in the battery process in the electrodes will become more important as the layer thickness increases. Laser structuring of the electrodes can counteract these processes and will also improve the high current capability. Finally, LIBs with high-energy and high-power density can be realized by introducing laser generated electrode architectures (3D battery concept), i.e., at the same time, improved electrolyte transfer in thick film electrodes and improved lithium ion transport kinetics are achieved. For developing next generation batteries including the 3D battery concept for large footprint areas, high energy materials such as nickel-enriched Lithium-Nickel-Manganese-Cobalt-Oxide (NMC) for cathodes and silicon-based anodes are introduced.

Aerosol extraction and direct laser ablation ICP-MS analysis of the fine and ultrafine fractions of regolith

The <10, <4, <2.5 and <1 µm fractions of eight regolith samples have been extracted as aerosols, then analysed for more than 60 elements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Precision and accuracy rivals that of conventional digestion and ICP-MS analysis for most elements, but the aerosol extraction and ablation approach can be completed within 30 min, avoids compromising the sample by screening, column settling, fusion and/or digestion, and includes data for elements such as Br, Cl, I and Se that are conventionally analysed by individual procedures. Major element chemistry and scanning electron microscope (SEM) imagery show that the aerosol fractions of regolith are dominated by kaolinite, with quartz in aeolian regolith. The aerosol fractions of Si- and Ca-rich regolith have higher trace element concentrations than the coarser fraction (0.45–2 mm), but chalcophile elements are depleted in the aerosols of Fe-rich regolith relative to the coarser fraction. Improvements in in-field analytical technology coupled with aerosol extraction mean that fine and ultrafine fraction chemistry can be used to guide mineral exploration programmes in close to real time. Supplementary material : The results of the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis of filter papers are available at https://doi.org/10.6084/m9.figshare.c.4562807

Femtosecond laser induced periodic surface structures for the enhancement of field emission properties of tungsten

Direct femtosecond laser ablation enables the maskless fabrication of nano- and micro-scale structures on variety of materials. A typical example is the formation of femtosecond Laser Induced Periodic Surface Structures (fs-LIPSSs), which can lead to strong modification in electrical, optical, wetting, and field emission properties of materials. Here, we study the field emission properties of fs-LIPSSs. We created fs-LIPSSs and fs-LIPSSs covered with nano- and micro-scale structures at different laser fluences on Tungsten (W) and showed that these structures offer significant enhancement in electron field emission properties. We provide a phenomenological model to explain the enhancement of electron emission parameters. The enhancement in the field emission properties of laser irradiated W is explained based on the convergence of electric field lines at the ridges of the fs-LIPSSs and fs-LIPSSs covered with nanoscale structures, which in turn, enhances the local field intensity and the electron emission parameters. The direct fabrication of 1D subwavelength structures is an important step towards the creation of low-cost cathodes for various potential applications.

Fabrication of micro-channels on Al2O3/TiC ceramics using picosecond laser induced plasma micromachining

Laser induced plasma micromachining (LIPMM) using a 10 ps laser was applied to create micro-channels on the surface of Al2O3/TiC ceramic. Micro-channels were firstly created by direct laser ablation and LIPMM to comparatively assess the machining ability of two processes. The results showed that LIPMM could create micro-channels with a higher depth and better surface morphologies as compared to direct laser ablation. Subsequently, the influence of laser parameters during LIPMM like pulse energy, scanning speed and frequency on the machining characteristics was investigated. The machined depth of the micro-channel increased with an increase in pulse energy, meanwhile an increase in frequency or a decrease in scanning speed increased the overlap, leading to an increment of the machined depth as well. The pulse energy, scanning speed and frequency had a slight effect on the machined width. The width of heat affected zone increased with the increasing overlap and pulse energy.

Fabrication of sapphire rib waveguides using a femtosecond laser

We demonstrate a method for fabricating sapphire rib waveguides with femtosecond laser micromachining technology. Finite difference beam propagation method (FD-BPM) is applied to design sapphire rib waveguides. We explore the process of etching on a sapphire substrate surface via direct laser ablation. Rib waveguides that satisfies the dimensions of our design were fabricated. Actual light propagation performance is tested, and with the cut-back method, the insertion loss of 2.9±0.5 dB/cm is measured.

Superhydrophobic polytetrafluoroethylene surfaces with accurately and continuously tunable water adhesion fabricated by picosecond laser direct ablation

Superhydrophobic polytetrafluoroethylene (PTFE) surfaces with accurately and continuously tunable water adhesion were fabricated by a simple and rapid method of picosecond (ps) laser direct ablation. By simply changing laser scan intervals (LSIs) from 5 to 140 μm, three laser-ablated PTFE surfaces, i.e., the two superhydrophobic surfaces with ultralow water adhesion and with tunable water adhesion, and the ordinary hydrophobic surface with ultrahigh water adhesion, could be obtained. Here, the sliding angles of water droplets on these surfaces could be continuously varied from about 1° to about 90°. XPS analysis suggested that the continuous variations of water adhesion and wettability were probably attributed to the change of surface microstructure and not to that of chemical composition. SEM analysis showed that different LSIs resulted in different surface microstructures and different area ratios of the laser-ablated regions to the pristine regions. This was because of the composite ablation process of photothermal and photochemical effects of the special ps laser wavelength (355 nm) and pulse duration (about 10 ps). The tunable water adhesion was verified by the coalescence-induced droplets jumping behavior. This study will provide a novel and versatile method for the rapid fabrication of superhydrophobic material surfaces with accurately and continuously tunable adhesion.

Laser Inscription of Microfluidic Devices for Biological Assays.

A rapid and direct CO2 laser ablation method was developed to create superhydrophilic surfaces and arrays of hydrophobic-superhydrophilic patterns for application in bioassays. Here, a combination of superhydrophilic and hemiwicking wetting characteristics was exploited to create microfluidic slides that were used as biological assays that prevented cell aggregation. This feature allowed microscopic analyses to be carried out at the individual cell level. This bioassay enabled control of cell population in localized areas (15 cells cm-2). The device had 84% transparency, allowing direct fluorescence microscopy measurements in transmission mode. High adhesion of aqueous fluids on superhydrophilic areas surrounded by superhydrophobic boundaries provided selective retention and confinement. The adhered droplets maintained retention under 180° substrate tilt. These architectures provided rapid self-partitioning of the liquid into an array of droplets. The hydrophobic-superhydrophilic patterned arrays may have applications in microfluidic bioassays, high-throughput screening, and medical diagnostics.

Single-Mode Lasing from Imprinted Halide-Perovskite Microdisks.

Halide-perovskite microlasers have demonstrated fascinating performance owing to their low-threshold lasing at room temperature and low-cost fabrication. However, being synthesized chemically, controllable fabrication of such microlasers remains challenging, and it requires template-assisted growth or complicated nanolithography. Here, we suggest and implement an approach for the fabrication of microlasers by direct laser ablation of a thin film on glass with donut-shaped femtosecond laser beams. The fabricated microlasers represent MAPbBr xI y microdisks with 760 nm thickness and diameters ranging from 2 to 9 μm that are controlled by a topological charge of the vortex beam. As a result, this method allows one to fabricate single-mode perovskite microlasers operating at room temperature in a broad spectral range (550-800 nm) with Q-factors up to 5500. High-speed fabrication and reproducibility of microdisk parameters, as well as a precise control of their location on a surface, make it possible to fabricate centimeter-sized arrays of such microlasers. Our finding is important for direct writing of fully integrated coherent light sources for advanced photonic and optoelectronic circuitry.

Rapid Engraving of Artificial Compound Eyes from Curved Sapphire Substrate

AbstractWith high thermal and mechanical stability, glass artificial compound eyes have great potential applications in wide field‐of‐view (FOV) imaging and fast detection. However, the rapid fabrication of large‐area, high integration, uniform, and well‐designed three‐dimensional (3D) glass compound eyes is still a great challenge. Here, a dry‐etching‐assisted femtosecond laser machining (DE‐FsLM) technology is proposed for fabrication of cm‐sized concave compound eye from a curved sapphire substrate, with which the fabrication efficiency can be improved by over two orders of magnitude compared with direct laser ablation. With high hardness and thermal stabilities, the sapphire concave compound eyes can be used as high‐temperature and hard‐casting templates for the replication of convex compound eyes on K9 glass. The replicated cm2‐size all‐glass compound eye consists of a spherical macrolens (1 cm diameter and 2.3 mm height) and over 190 000 close‐packed ommatidia (≈20 µm diameter and 1.5 µm height). The compound eyes exhibit excellent optical properties with wide FOV (up to 90°) imaging and focusing. These results indicate that the DE‐FsLM and casting replication technology will open new opportunities in micro‐/nanofabrication of hard materials.

Laser-processed diffractive lenses for the frequency range of 4.7 THz.

The development of diffractive lenses for the upper terahertz (THz) frequency range above 1 THz was successfully demonstrated by employing a direct laser ablation (DLA) technology. Two types of samples such as the Soret zone plate lens and the multi-level phase-correcting Fresnel lens were fabricated of a metal foil and crystalline silicon, respectively. The focusing performance along the optical axis of a 4.745 THz quantum cascade laser beam with respect to the positioning angle of the sample was studied by using a real-time microbolometric camera. A binary-phase profile sample demonstrated the values of the focusing gain and focused beam size up to 25 dB and 0.15 mm (2.4λ), respectively. The increase of the phase quantization level to eight led to higher (up to 29 dB) focusing gain values without a measurable increase of optical losses. All the samples were tolerant to misalignment as large as 10 deg of oblique incidence with a focusing power drop no larger than 10%. The results pave the way for new applications of industry-ready DLA technology in the entire THz range.

Comparative Experimental Investigation of Micro-channel Fabrication in Ti Alloys by Laser Ablation and Laser-induced Plasma Micro-machining

Abstract Reliable and improved micro-fabrication processes for high-strength alloys are needed due to their increasing use in micro-scale applications. Laser-Induced Plasma Micro-Machining (LIPMM) has been shown to have several advantages over conventional direct laser ablation. In this study micro-channels are fabricated in Ti-6Al-4V, one of the difficult-to-machine materials, to compare the micro-manufacturing capabilities of direct laser ablation to LIPMM. It has been shown that LIPMM results in much deeper channels and higher aspect ratios and better machining consistency than direct laser ablation.

Dynamic Spallation in Uranium under Laser Shock Loading**Supported by the Science Foundation of China Academy of Engineering Physics under Grant No A090504.

The spall behavior of uranium is investigated using direct laser ablation loading experiments. The uranium targets are cut and ground to 0.05 mm, 0.1 mm, and 0.15 mm in thickness. Laser energies are varied to yield a constant peak pressure. This results in different strain rates and varying degrees of damage to the uranium targets. The spall strength is calculated and analyzed from the free surface velocity histories recorded using a line velocity interferometer for any reflections system. The spall strength increases from 4.3 GPa to 9.4 GPa with strain rates ranging from 4.0 × 106 s−1 to 1.7 × 107 s−1. Post-mortem analysis is performed on the recovered samples, revealing the twin-matrix interfaces together with the inclusions to be the primary factor governing the spall fracture of uranium.

Size Modification of Optically Active Contamination‐Free Silicon Nanoparticles with Paramagnetic Defects by Their Fast Synthesis and Dissolution

Contamination‐free silicon‐based nanoparticles (NPs) with several modalities are developed in this work. They are formed by non‐toxic laser‐assisted decomposition of silicon microgranules homogeneously dispersed in deionized water. Precise control of numerous experimental parameters allows repeatable fine tuning of nanoparticle size solving significant lacks of a direct laser ablation routine. Such a method provokes a huge amount of paramagnetic defect states of optically active silicon NPs that can serve as a contrast agent for magnetic resonance and nonlinear optical imaging. Perspectives of their bioapplication are driven by detected their fast size degradation in a NaCl‐based medium.

Comparison of Direct and Indirect Laser Ablation of Metallized Paper for Inexpensive Paper-Based Sensors.

In this work, we present a systematic study of laser processing of metallized papers (MPs) as a simple and scalable alternative to conventional photolithography-based processes and printing technologies. Two laser-processing methods are examined in terms of selectivity for the removal of the conductive aluminum film (25 nm) of an MP substrate; these processes, namely direct and indirect laser ablation (DLA and ILA), operate at wavelengths of 1.06 μm (neodymium-doped yttrium aluminum garnet) and 10.6 μm (CO2), respectively. The required threshold energy for each laser processing method was systematically measured using electrical, optical, and mechanical characterization techniques. The results of these investigations show that the removal of the metal coating using ILA is only achieved through partial etching of the paper substrate. The ILA process shows a narrow effective set of laser settings capable of removing the metal film while not completely burning through the paper substrate. By contrast, DLA shows a more defined and selective removal of the aluminum layer without damaging the mechanical and natural fibular structure of the paper substrate. Finally, as a proof of concept, interdigitated capacitive moisture sensors were fabricated by means of DLA and ILA onto the MP substrate, and their performance was assessed in the humidity range of 2-85%. The humidity sensitivity results show that the DLA sensors have a superior humidity sensing performance compared to the ILA sensors. The observed behavior is attributed to the higher water molecule absorption and induced capillary condensation within the intact cellulose network resulting from the DLA process (compared to the damaged one from the ILA process). The DLA process of MP should enable scalable production of low-cost, paper-based physical and chemical sensing systems for potential use in point-of-care diagnostics and food packaging.