Metamaterial absorber was used for a background-suppressed surface-enhanced molecular detection technique. By utilizing the resonant coupling between plasmonic modes of a metamaterial absorber and infrared (IR) vibrational modes of a self-assembled monolayer (SAM), attomole level molecular sensitivity was experimentally demonstrated. IR absorption spectroscopy of molecular vibrations is of importance in chemical, material, medical science and so on, since it provides essential information of the molecular structure, composition, and orientation. In the vibrational spectroscopic techniques, in addition to the weak signals from the molecules, strong background degrades the signal-to-noise ratio, and suppression of the background is crucial for the further improvement of the sensitivity. Here, we demonstrate low-background resonant Surface enhanced IR absorption (SEIRA) by using the metamaterial IR absorber that offers significant background suppression as well as plasmonic enhancement. By using mask-less laser lithography technique, metamaterial absorber which consisted of 1D array of Au micro-ribbons on a thick Au film separated by a transparent gap layer made of MgF₂ was fabricated. This metamaterial structure was designed to exhibit an anomalous IR absorption at ~ 3000 cm^-1, which spectrally overlapped with C-H stretching vibrational modes. 16-Mercaptohexadecanoic acid (16-MHDA) was used as a test molecule, which formed a 2-nm thick SAM with their thiol head-group chemisorbed on the Au surface. In the FTIR measurements, the symmetric and asymmetric C-H stretching modes were clearly observed as reflection peaks within a broad plasmonic absorption of the metamaterial, and 1.8 attomole molecular sensitivity was experimentally demonstrated.

The unique properties of ultrashort laser pulses and the decrease of invest pave the way to numerous novel applications. Even in the very price sensitive field of laser marking, ultrashort laser can compete due to a new cost structure and remarkable properties of the marking results. In this study we concentrated on industrial marking of medical equipment by using IR ultrashort lasers and compared the results with common marking laser systems. We demonstrate the benefits of ultrashort lasers marking on chirurgical devices, observing the influence of pulse energy, pulse duration, scanning velocity in respect to the visibility, corrosion resistance and long term durability under clinical conditions. Nowadays many parts and products are marked for the purpose of identification and traceability. One kind of laser marking is the well known annealing of stainless steel by nanosecond marking lasers. When annealing occurs a colored oxide layer grows due to the local heating of the material surface. Compared to the raw material, the annealed marking shows increased corrosion sensitivity. Regarding the traceability, the poor durability of the ns marking resulting in contrast reduction and the corrosion susceptibility are a huge problem. Therefore three different laser sources with ns-psfs pulse duration were observed. The focus rests on the realization of parameter studies (various lasers) and their effect on the corrosion and passivation behavior. Furthermore analysis of the oxide layers by use of EDX and XRD were performed to obtain further information on the composition and structure of the markings.

Cutting and drilling of transparent materials using short pulsed laser systems are important industrial production processes. Applications ranging from sapphire cutting, hardened glass processing, and flat panel display cutting, to diamond processing are possible.

The ablation process using a Gaussian laser beam incident on the topside of a sample with several parallel overlapping lines leads to a V-shaped structured groove. This limits the structuring depth for a given kerf width. The unique possibility for transparent materials to start the ablation process from the backside of the sample is a well-known strategy to improve the aspect ratio of the ablated features. This work compares the achievable groove depth depending on the kerf width for front-side and back-side ablation and presents the best relation between the kerf width and number of overscans. Additionally, the influence of the number of pulses in one burst train on the ablation efficiency is investigated. The experiments were carried out using Spirit HE laser from Spectra-Physics, with the features of adjustable pulse duration from <400 fs to 10 ps, three different repetition rates (100 kHz, 200 kHz and 400 kHz) and average output powers of >16 W ( at 1040 nm wavelength).

A combination of a cylindrical lens with a spherical lens was used to create an elliptical beam shape on the surface of the processed workpieces in order to increase the ablation efficiency producing linear grooves. Near-infrared 8 ps laser pulses with energies of up to 2.3 mJ were applied at a repetition rate of 300 kHz to ablate the grooves on the surface of the samples. The ablation rates obtained at different feed rates were examined. At a peak fluence of 4 J/cm², an power specific ablation rate of almost 0.4 mm³/min/W was achieved for a beam with an ellipticity of 0.9955.

Lab-on-a-chip devices have been intensively developed during the last decade when emerging technologies offered possibilities to manufacture reliable devices with increased spatial resolution. These biochips allowed testing chemical reactions in nanoliter volumes with enhanced sensitivity and lower consumption of reagents. There is space to further consolidate biochip assembling processing since the new technologies attempt direct fabrication in view of reducing costs and time by increasing efficiency and functionalities.

Rapid prototyping by ultrafast lasers which induces local modifications inside transparent materials of both glass and polymers with high precision at micro- and nanoscale is a promising tool for fabrication of such biochips. We have developed a new technology by combining subtractive ultrafast laser assisted chemical etching of glasses and additive two-photon polymerization to integrate 3D glass microfluidics and polymer microcomponents in a single biochip. The innovative hybrid "ship-in-a-bottle" approach is not only an instrument that can tailor 3D environments but also a tool to fabricate biomimetic in vivo structures inside a glass microfluidic chip. It was possible to create appropriate environment for cell culturing and to offer robustness and transparency for optical interrogation. Cancer cells were cultivated inside biochips and monitored over short and long periods. With the view of understanding cancer cells specific behavior such as migration or invasiveness inside human body, introduction of different geometrical configurations and chemical conditions were proposed. The cells were found responsive to a gradient of nutrient concentration through the microchannels of a 3D polymeric scaffold integrated inside glass biochip.

The resulting surface roughness and waviness after processing with ultra-short pulsed laser radiation depend on the laser parameters as well as on the machining strategy and the scanning system. However the results depend on the material and its initial surface quality and finishing as well. The improvement of surface finishing represents effort and produces additional costs. For industrial applications it is important to reduce the preparation of a workpiece for laser micro-machining to optimize quality and reduce costs.

The effects of the ablation process and the influence of the machining strategy and scanning system onto the surface roughness and waviness can be differenced due to their separate manner. By using the optimal laser parameters on an initially perfect surface, the ablation process mainly increases the roughness to a certain value for most metallic materials. However, imperfections in the scanning system causing a slight variation in the scanning speed lead to a raise of the waviness on the sample surface.

For a basic understanding of the influence of grinding marks, the sample surfaces were initially furnished with regular grooves of different depths and spatial frequencies to gain a homogenous and well-defined original surface. On these surfaces the effect of different beam waists and machining strategy are investigated and the results are compared with a simulation of the process. Furthermore the behaviors of common surface finishes used in industrial applications for laser micro-machining are studied and the relation onto the resulting surface roughness and waviness is presented.

Femtosecond laser writing in glasses is a growing field of research and development in photonics, since it provides a versatile, robust and efficient approach to directly address 3D material structuring. Laser-glass interaction process has been studied for many years, especially the local changes of the refractive index that have been classified by three distinct types (types I, II and III, respectively). These refractive index modifications are widely used for the creation of photonics devices such as waveguides [1], couplers, photonic crystals to fabricate integrated optical functions in glasses for photonic applications as optical circuits or integrated sensors.

Femtosecond laser writing in a home-developed silver containing zinc phosphate glasses induces the creation of fluorescent silver clusters distributed around the laser-glass interaction voxel [2]. In this paper, we introduce a new type of refractive index modification in glasses. It is based on the creation of these photo-induced silver clusters allowing a local change in the refractive index Δn = 5×10^-3, which is sufficient for the creation of waveguides and photonics devices. The wave guiding process in our glasses along these structures with original geometry is demonstrated for wavelengths from visible to NIR [3], giving a promising access to integrated optical circuits in these silver containing glasses. Moreover, the characterization of the waveguides is presented, including their original geometry, the refractive index change, the mode profile, the estimation of propagation losses and a comparison with simulation results.

1. K. M. Davis, K. Miura, N. Sugimoto, and K. Hirao, Opt. Lett. 21, 1729-1731 (1996).

2. M. Bellec, A. Royon, K. Bourhis, J. Choi, B. Bousquet, M. Treguer, T. Cardinal, J.-J. Videau, M. Richardson, and L. Canioni, The Journal of Physical Chemistry C 114, 15584-15588 (2010).

3. S. Danto, F. Désévédavy, Y. Petit, J.-C. Desmoulin, A. Abou Khalil, C. Strutynski, M. Dussauze, F. Smektala, T. Cardinal, and L. Canioni, Advanced Optical Materials 4, 162-168 (2016).

In this work we investigate new degrees of freedom in controlling the physical properties of structured photo-sensitive materials that can be usefully exploited in many application fields. We employ azopolymers, a class of light responsive materials, which are structured in micro-pillar array. A reversible and controlled change in morphology of a pre-patterned polymeric film under properly polarized illumination is demonstrated to provide the opportunity to engineer surface structures and dynamically tune their properties. We exploit the laser process taking advantage of the light-induced deformation of a micro-textured azopolymeric film in order to modify the surface hydrophobicity along specific direction.

In the conventional femtosecond laser direct writing with a Gaussian beam, the focus is an ellipsoid with the long axis along the beam propagation direction, resulting in the ellipsoidal fabricated dot. Due to the simple shape of the dot, complex three-dimensional (3D) nano/microstructures should be written dot by dot by the focus scanning, which is usually time-consuming. Therefore, a rapid nano/microfabrication technique is becoming highly desired to achieve arbitrary 3D nano/microstructures. By 2D phase modulation of the Gaussian beam, multi-focuses were generated for the direct writing of several same nano/microstructures simultaneously to save fabrication time, and donut and other 2D intensity distributions were produced for the single exposure fabrication of 2D microstructures. Here, we demonstrate the single-exposure two-photon polymerization of a 3D microstructure via the 3D focal field engineering by using the 2D phase-only spatial light modulation. With a single exposure, a whole 3D microstructure like a double-helix is polymerized simultaneously, whose configuration is controlled by the designed 3D focal intensity distribution. In addition, a longitudinal circular intensity distribution is generated for the multi-photon inscription of a depressed cladding waveguide inside glass with single scan transverse writing.

We present a preliminary experimental chemical-physical characterisation of the structural modification of Gallium Lanthanum Sulfide (GLS) glass occurring during ultrafast laser inscription of waveguides in thermal regime. Our measurements with a micro-Raman spectrograph confirmed previous reports of negligible chemical modification of the irradiated glass. Additionally, the observed onset of significant long-range stress patterns surrounding the irradiated regions indicate that GLS is subject to an irradiation-induced densification of the glass network. We discuss the consequences of these observations for the amelioration of the laser inscription techniques in chalcogenide glasses and, potentially, for the understanding of their microscopic structure.

Layer-based laser ablation of three dimensional micro structured freeform surfaces has become of significant importance for technical applications such as biomimetic surfaces in recent years. In order to identify the optimum set of process parameters for a complex laser ablation operation, a design of experiments (DoE) study has been carried out with laser sources covering pulse durations regime of femtosecond (fs), picosecond (ps) and nanosecond (ns). The aim was to identify the optimum parameter set for achieving best surface roughness and, as a second criteria, for machining time to be reduced to a minimum. In a first step, rectangular pockets have been machined and a DoE based parameter variation was performed. In particular, the parameters wavelength (1030 nm, 515 nm, 343 nm), machining speed, laser power, and laser pulse duration (fs, ps, ns) have been modified. Surface roughness and ablated depth were measured and an optimum set of parameters was calculated. The results show that the ultraviolet laser type (343nm) has the best performance to achieve lowest surface roughness and with a laser pulse duration of 3445 fs reaches also the best ablation efficiency in relation to machining time. While machining speed and laser power have an almost linear influence on achievable roughness, laser pulse duration has a quadratic influence in relation to a global minimum on the surface roughness result. For the ablated depth, machining speed and laser power have an almost linear influence while laser pulse duration has a quadratic influence in relation to a global maximum.

Microfluidic optical stretchers are valuable optofluidic devices for studying single cell mechanical properties. These usually consist of a single microfluidic channel where cells, with dimensions ranging from 5 to 20 μm are trapped and manipulated through optical forces induced by two counter-propagating laser beams. Recently, monolithic optical stretchers have been directly fabricated in fused silica by femtosecond laser micromachining (FLM). Such a technology allows writing in a single step in the substrate volume both the microfluidic channel and the optical waveguides with a high degree of precision and flexibility. However, this method is very slow and cannot be applied to cheaper materials like polymers. Therefore, novel technological platforms are needed to boost the production of such devices on a mass scale.

In this work, we propose integration of FLM with micro-injection moulding (μIM) as a novel route towards the cost-effective and flexible manufacturing of polymeric Lab-on-a-Chip (LOC) devices. In particular, we have fabricated and assembled a polymethylmethacrylate (PMMA) microfluidic optical stretcher by exploiting firstly FLM to manufacture a metallic mould prototype with reconfigurable inserts. Afterwards, such mould was employed for the production, through μIM, of the two PMMA thin plates composing the device. The microchannel with reservoirs and lodgings for the optical fibers delivering the laser radiation for cell trapping were reproduced on one plate, while the other included access holes to the channel. The device was assembled by direct fs-laser welding, ensuring sealing of the channel and avoiding thermal deformation and/or contamination.

We present the development of laser processes for flexible OPV on roll-to-roll (RR2R) produced thin film barrier with indium tin oxide (ITO) as transparent conductive (TC) bottom electrode. Direct laser structuring of ITO on such barrier films (so-called P1 process) is very challenging since the layers are all transparent, a complete electrical isolation is required, and the laser process should not influence the barrier performance underneath the scribes. Based on the optical properties off the SiN and ITTO, ultra-short pulse lasers inn picosecond and femtosecond regime with standard infrared (IR) wavelength as well as lasers with new a wavelength (22 μm regime) are tested for this purpose. To determine a process window for a specific laser a fixed methodology is adopted. Single pulse ablation tests were followed by scribing experiments where the pulse overlap was tuned by varying laser pulse fluence, writing speed and frequency. To verify that the laser scribing does not result inn barrier damage underneath, a new test method was developed based on the optical Ca-test. This method shows a clear improvement in damage analysis underneath laser scribes over normal optical inspection methods (e.g. microscope, optical profiler, SEM). This way clear process windows can be obtained for IR TC patterning.

The proper long term operation of organic electronic devices like organic photovoltaics OPV depends on their resistance to environmental influences such as permeation of water vapor. Major efforts are spent to encapsulate OPV. State of the art is sandwich-like encapsulation between two ultra-barrier foils. Sandwich encapsulation faces two major disadvantages: high costs (~1/3 of total costs) and parasitic intrinsic water (sponge effects of the substrate foil).

To fight these drawbacks, a promising approach is to use the OPV substrate itself as barrier by integration of an ultra-barrier coating, followed by alternating deposition and structuring of OPV functional layers. In effect, more functionality will be integrated into less material, and production steps are reduced in number. All processing steps must not influence the underneath barrier functionality, while all electrical functionalities must be maintained.

As most reasonable structuring tool, short and ultrashort pulsed lasers USP are used. Laser machining applies to three layers: bottom electrode made of transparent conductive materials (P1), organic photovoltaic operative stack (P2) and top electrode (P3).

In this paper, the machining of functional ~110…250 nm layers of flexible OPV by USP laser systems is presented. Main focus is on structuring without damaging the underneath ultra-barrier layer. The close-to-process machining quality characterization is performed with the analysis tool “hyperspectral imaging” (HSI), which is checked crosswise with the "gold standard" Ca-test. It is shown, that both laser machining and quality controlling, are well suitable for R2R production of OPV.

For next generation of high energy lithium-ion batteries, silicon as anode material is of great interest due to its higher specific capacity (3579 mAh/g). However, the volume change during de-/intercalation of lithium-ions can reach values up to 300 % causing particle pulverization, loss of electrical contact and even delimitation of the composite electrode from the current collector. In order to overcome these drawbacks for silicon anodes we are developing new 3D electrode architectures. Laser nano-structuring of the current collectors is developed for improving the electrode adhesion and laser micro-structuring of thick film composite electrodes is applied for generating of freestanding structures. Freestanding structures could be attributed to sustain high volume changes during electrochemical cycling and to improve the capacity retention at high C-rates (> 0.5 C). Thick film composite Si and Si/graphite anode materials with different silicon content were deposited on current collectors by tape-casting. Film adhesion on structured current collectors was investigated by applying the 90° peel-off test. Electrochemical properties of cells with structured and unstructured electrodes were characterized. The impact of 3D electrode architectures regarding cycle stability, capacity retention and cell life-time will be discussed in detail.

Lithium-ion batteries became the most promising types of mobile energy storage devices due to their high gravimetric and volumetric capacity, high cycle life-time, and low self-discharge. Nowadays, the cathode material lithium nickel manganese cobalt oxide (NMC) is one of the most widely used cathode material in commercial lithium-ion batteries due to many advantages such as high energy density (>150 Wh kg^-1) on cell level, high power density (650 W kg-1 @ 25 °C and 50 % Depth of Discharge) [1], high specific capacity (163 mAh g^-1) [2], high rate capability and good thermal stability in the fully charged state. However, in order to meet the requirements for the increasing demand for rechargeable high energy batteries, nickel-rich NMC electrodes with specific capacities up to 210 mAh g^-1 seem to be the next generation cathodes which can reach on cell level desired energy densities higher than 250 Wh kg^-1 [3]. Laser-structuring now enables to combine both concepts, high power and high energy lithium-ion batteries. For this purpose, lithium nickel manganese cobalt oxide cathodes were produced via tape casting containing 85-90 wt% of active material with a film thickness of 50-260 μm. The specific capacities were measured using galvanostatic measurements for different types of NMC with varying nickel, manganese and cobalt content at different charging/discharging currents ("C-rates"). An improved lithium-ion diffusion kinetics due to an increased active surface area could be achieved by laser-assisted generating of three dimensional architectures. Cells with unstructured and structured cathodes were compared. Ultrafast laser ablation was used in order to avoid a thermal impact to the material. It was shown that laser structuring of electrode materials leads to a significant improvement in electrochemical performance, especially at high charging and discharging C-rates.

Laser-induced periodic surface structures (LIPSS, ripples) are a universal phenomenon that can be observed on almost any material after the irradiation by linearly polarized laser beams, particularly when using ultrashort laser pulses with durations in the picosecond to femtosecond range. During the past few years significantly increasing research activities have been reported in the field of LIPSS, since their generation in a single-step process provides a simple way of nanostructuring and surface functionalization towards the control of optical, mechanical or chemical properties. In this contribution current applications of LIPSS are reviewed, including the colorization of technical surfaces, the control of surface wetting, the tailoring of surface colonization by bacterial biofilms, and the improvement of the tribological performance of nanostructured metal surfaces.

Micro-supercapacitors with small size, light weight, flexibility while maintaining high energy and power output are required for portable miniaturized electronics. The fabrication methods and materials should be cost-effective, scalable, and easily integrated to current electronic industry. Carbon materials have required properties for high-performance flexible supercapacitors, including high specific surface areas, electrochemical stability, and high electrical conductivity, as well as the high mechanical tolerance. Laser direct writing method is a non-contact, efficient, single-step fabrication technique without requirements of masks, post-processing, and complex clean room, which is a useful patterning technique, and can be easily integrated with current electronic product lines for commercial use. Previously we have reported micro-supercapacitors fabricated by laser direct writing on polyimide films in air or Ar, which showed highcapacitive performance. However, the conductivity of the carbon materials is still low for fast charge-discharge use. Here, we demonstrated the fabrication of flexible carbon/Au composite high-performance MSCs by first laser direct writing on commercial polyimide films followed by spin-coating Au nanoparticles ink and second in-situ laser direct writing using the low-cost semiconductor laser. As-prepared micro-supercapacitors show an improved conductivity and capacitance of 1.17 mF/cm² at a high scanning rate of 10,000 mV/s, which is comparable to the reported capacitance of carbon-based micro-supercapacitors. In addition, the micro-supercapacitors have high bend tolerance and long-cycle stability.

With the developing of wearable electronics and information society, integrated energy storage devices are urgently demanded to be integrated on flexible substrates. We successfully demonstrated using direct laser-reduction of the hydrated GO and chloroauric acid (HAuCl4) nanocomposite to fabricate in-plane micro-supercapacitors (MSCs) with fast ion diffusion on paper. The electrode conductivity of these flexible nanocomposites reaches up to 1.1 x 10⁶ S m^-1, which enhances superior rate capability of micro-supercapacitors, and large specific capacitances of 0.77 mF cm^-2 (17.2 F cm^-3 for volumetric capacitance) at 1 V s^-1, and 0.46 mF cm^-2 (10.2 F cm^-3) at 100 V s^-1. We also have demonstrated that pulsed laser irradiation rapidly converts the polyimide (PI) sheets into an electrically conductive porous carbon structure in ambient conditions. The specific capacitance of single layer surface supercapacitors can reach 20.4 mF/cm² at 0.1 mA/cm² discharge current density. Furthermore, we successfully fabricate the multi-layer supercapacitor with the PI substrate using 3D femtosecond laser direct writing, and the specific capacitances of three layers supercapacitors is 37.5 mF/cm².

Lithium nickel manganese cobalt oxide (Li(Ni_1/3Mn_1/3Co_1/3)O₂, NMC) thick film electrodes were manufactured by using the doctor-blade technique (tape-casting). Ultrafast laser-structuring was performed in order to improve the electrochemical performance. For this purpose, three-dimensional (3D) micro-structures such as free standing micropillars were generated in NMC cathodes by using femtosecond laser ablation. Laser-induced breakdown spectroscopy (LIBS) was used for post-mortem investigation of the lithium distribution of unstructured and femtosecond laser-structured NMC electrodes. For achieving a variable State-of-Health (SoH), both types of electrodes were electrochemically cycled. LIBS calibration was performed based on NMC electrodes with defined lithium amount. Those samples were produced by titration technique in a voltage window of 3.0 V - 5.0 V. Elemental mapping and elemental depth-profiling of lithium with a lateral resolution of 100 μm were applied in order to characterize the whole electrode surface. The main goal is to develop an optimized 3D cell design with improved electrochemical properties which can be correlated to a characteristic lithium distribution along 3D micro-structures at different SoH.

Surfaces equipped with periodic patterns with feature sizes in the micrometer, submicrometer and nanometer range present outstanding surface properties. Many of these surfaces can be found on different plants and animals. However, there are few methods capable to produce such patterns in a one-step process on relevant technological materials. Direct laser interference patterning (DLIP) provides both high resolution as well as high throughput. Recently, fabrication rates up to 1 m²·min^-1 could be achieved. However, resolution was limited to a few micrometers due to typical thermal effects that arise when nanosecond pulsed laser systems are used. Therefore, this study introduces an alternative to ns-DLIP for the fabrication of multi-scaled micrometer and submicrometer structures on nickel surfaces using picosecond pulses (10 ps at a wavelength of 1064 nm). Due to the nature of the interaction process of the metallic surfaces with the ultrashort laser pulses, it was not only possible to directly transfer the shape of the interference pattern intensity distribution to the material (with spatial periods ranging from 1.5 μm to 5.7 μm), but also to selectively obtain laser induce periodic surface structures with feature sizes in the submicrometer and nanometer range. Finally, the structured nickel sleeves are utilized in a roll-to-roll hot embossing unit for structuring of polymer foils. Processing speeds up to 25 m·min-1 are reported.

Heat-assisted magnetic recording (HAMR) has the potential to keep increasing the areal density in next generation hard disc drives (HDDs) by producing a nanoscale laser spot using optical antenna, called near field transducer (NFT) to locally and temporally heat a sub-diffraction-limited region in the recording medium. The NFTs made of plasmonic nanoscale optical antenna provide the capability of sub-wavelength light focusing at optical frequencies. These antennas are designed using both plasmonic resonance and localized plasmons to produce an enhance field in an area far below the diffraction limit. To reduce the selfheating effect in the NFT, which could cause materials failure that leads to degradation of the overall hard drive performance, the NFT must deliver sufficient power to the recording medium with as small as possible incident laser power. In this paper, the design and characterization of these plasmonic antennas and the effect of optical properties on field localization, absorption, and coupling efficiency will be discussed. Computations of heat dissipation and the induced temperature rise in NFT are carried out to study their dependence on materials’ properties. With the recent significant interests in searching for alternative low-loss plasmonic materials in the visible and near infrared range, the possibility of using alternative plasmonic materials for delivering higher power and simultaneously reducing heating in NFT are investigated.

Metal nanowire fabrication has drawn tremendous attention in recent years due to its wide application in electronics, optoelectronics, and plasmonics. However, conventional laser fabrication technologies are limited by diffraction limit thus the fabrication resolution cannot meet the increasingly high demand of modern devices. Herein we report on a novel method for high-resolution high-quality metal nanowire fabrication by using Hermite-Gaussian beam to ablate metal thin film. The nanowire is formed due to the intensity valley in the center of the laser beam while the surrounding film is ablated. Arbitrary nanowire can be generated on the substrate by dynamically adjusting the orientation of the intensity valley. This method shows obvious advantages compared to conventional methods. First, the minimum nanowire has a width of ~60 nm (≈1/13 of the laser wavelength), which is much smaller than the diffraction limit. The high resolution is achieved by combining the ultrashort nature of the femtosecond laser and the low thermal conductivity of the thin film. In addition, the fabricated nanowires have good inside qualities. No inner nanopores and particle intervals are generated inside the nanowire, thus endowing the nanowire with good electronic characteristics: the conductivity of the nanowires is as high as 1.2×10⁷ S/m (≈1/4 of buck material), and the maximum current density is up to 1.66×10⁸ A/m². Last, the nanowire has a good adhesion to the substrates, which can withstand ultrasonic bath for a long time. These advantages make our method a good approach for high-resolution high-quality nanowire fabrication as a complementary method to conventional lithography methods.

In this study, porous network structures were successfully created on various polymer surfaces by femtosecond laser micromachining. Six different polymers (poly(tetrafluoroethylene) (PTFE), poly(methyl methacrylate) (PMMA), high density poly(ethylene) (HDPE), poly(lactic acid) (PLA), poly(carbonate) (PC), and poly(ethylene terephthalate) (PET)) were machined at different fluences and pulse numbers, and the resulting structures were identified and compared by lacunarity analysis. At low fluence and pulse numbers, porous networks were confirmed to form on all materials except PLA. Furthermore, all networks except for PMMA were shown to bundle up at high fluence and pulse numbers. In the case of PC, a complete breakdown of the structure at such conditions was observed. Operation slightly above threshold fluence and at low pulse numbers is therefore recommended for porous network formation. Finally, the thickness over which these structures formed was measured and compared to two intrinsic material dependent parameters: the single pulse threshold fluence and the incubation coefficient. Results indicate that a lower threshold fluence at operating conditions favors material removal over structure formation and is hence detrimental to porous network formation. Favorable machining conditions and material-dependent parameters for the formation of porous networks on polymer surfaces have thus been identified.

The selective metallization on a flexible polymer film via laser direct writing and the following additive metallization process was studied as an alternate to conventional semi-additive process in the fabrication of printed circuit board. A Cu micropattern was fabricated on a polyimide film via CW blue-violet laser direct writing using a Cu nanoparticle ink and applied to a seed layer for the Cu electroplating. The on-demand processing of a Cu micropattern whose line width and thickness are ca. 5 and 2 μm, respectively, was achieved by combination of a laser-written seed micropattern and the following electro-plating. The homogeneity of the Cu micropatterns prepared from Cu nanoparticles was easily improved by combination with the following Cu plating.

Starting from a simple concept, transferring the shape of an interference pattern directly to the surface of a material, the method of Direct Laser Interference Patterning (DLIP) has been continuously developed in the last 20 years. From lamp-pumped to high power diode-pumped lasers, DLIP permits today for the achievement of impressive processing speeds even close to 1 m²/min. The objective: to improve the performance of surfaces by the use of periodically ordered micro- and nanostructures. This study describes 20 years of evolution of the DLIP method in Germany. From the structuring of thin metallic films to bulk materials using nano- and picosecond laser systems, going through different optical setups and industrial systems which have been recently developed. Several technological applications are discussed and summarized in this article including: surface micro-metallurgy, tribology, electrical connectors, biological interfaces, thin film organic solar cells and electrodes as well as decorative elements and safety features. In all cases, DLIP has not only shown to provide outstanding surface properties but also outstanding economic advantages compared to traditional methods.

Holographic line-shaped femtosecond processing was developed for large-area machining. It can be performed with high throughput in laser cutting, peeling, grooving, and cleaning of materials. We demonstrated the single-shot fabrication of a line structure in a glass surface using a line-shaped pulse generated by a holographic cylindrical lens displayed on a liquid-crystal spatial light modulator, a line-shaped beam deformed three-dimensionally for showing the potential of holographic line-shaped beam processing, laser peeling of an indium tin oxide film, in-process laser cleaning of debris on the surface of a fabricating sample, and laser grooving of stainless steel.

Exploitation of surface texturing by ultra-short pulse laser (UPL) technology for commercial purposes requires the undertaking of several issues including a reliable and robust set-up compatible with large area and high throughput production. A technological strategy to rise to this challenge could be the use of polygon scanner which can deflect a laser beam with unprecedented speed (up to some hundreds of m/s) over an optical field of some tens of cm, jointly with high average power UPL delivering pulse energies of few tens of micro joule and repetition rates in the range of MHz. Nevertheless, unwanted thermal effects are expected to arise, when utilising average power as high as several tens of Watts, compromising the surface texturing morphology. Here a study is reported on the surface texturing of stainless steel carried out utilising an industrial UPL emitting both in the near infrared (λ = 1030 nm) and visible (λ = 515 nm) with high average power (up to 20 W) and operating at high repetition rate (1 MHz). The impact of the fundamental process parameters like single pulse fluence, beam scan speed, number of successive scans and energy dose has been studied. The evolution of the surface morphology has been investigated using scanning electron microscopy (SEM) analysis. We believe our results will contribute to an in deep understanding of the UPL laser texturing with high power, as preliminary step to increase in the next future surface texturing by UPL technological readiness.

Periodic surface structures with micrometer or submicrometer resolution produced on surfaces of different technological parts can be used to improve their mechanical, biological or optical characteristics. While direct laser interference patterning (DLIP) already permits structuring speeds of up to 0.9 m²/min under constant process parameters, fabrication of individualized surface structures fabricated "on-the-fly" is not possible at high speeds. In this study, a scanner-based DLIP optical head is presented which combines the flexibility of the DLIP technology with a high-performance galvanometer scanner system. An evaluation of the structuring results as well as various application examples will be presented.

In industrial laser micro processing, throughput is as important as process quality. Treating large areas in minimum time is pivotal in achieving reduced unit costs in high-volume production. Excimer lasers meet the requirements for clean and precise structuring and enable the smallest structures in an efficient way. The latest technical developments in high power excimer lasers is bound to take cost-efficient UV-laser micro processing to the next level and bridges the gap between achievable precision and achievable throughput. New excimer laser developments and beam concepts together with latest performance data for upscaling both UV power and UV pulse energy will be the topic of this paper against the background of upcoming market trends and high volume applications.

Laser shock peening using low-energy nanosecond (ns) fiber lasers was investigated in this study to realize high-speed micro-scale laser shock peening on selected positions without causing surface damage. Due to the employment of a fiber laser with high-frequency and prominent environmental adaptability, the laser peening system is able to work with a much higher speed compared to traditional peening systems using Nd:YAG lasers and is promising for in-situ applications in harsh environments. Detailed surface morphology investigations both on sacrificial coatings and Al alloy surfaces after the fiber laser peening revealed the effects of focal position, pulse duration, peak power density, and impact times. Micro-dent arrays were also obtained with different spot-to-spot distances. Obvious micro-hardness improvement was observed inside the laser-peening-induced microdents after the fiber laser shock peening.

Mixing of lithographically processable materials with functional additives is one of the widely explored possibilities in the field of the laser material processing. In this work we investigate how gold nanoparticles (Au NP) influence the photosensitivity of SZ2080 and PEG-DA-700 – two materials commonly used in femtosecond 3D direct laser writing (DLW). Experimental study of achieved line widths as well as comparison of polymerization/optical damage threshold intensities allowed quantitatively define how Au NP change polymers’ response to ultrafast laser pulses. Light-material and plasmonic interaction theories are applied to explain this phenomena. Furthermore, we demonstrate how nanoprecision achieved with DLW can be employed to create functional micromechanical structures, namely negative Poisson coefficient metamaterial and chain-mail like flexible structure. Later one is produced using combination of linear stages and galvanoscanners, demonstrating nearly unlimited working area (in range of ∼cm) and very high translation velocity (∼mm/s) thus proving that DLW can be considered an industrial grade technology.

It is well known that micro and sub-micrometer periodical structures play a significant role on the properties of a surface. Ranging from friction reduction to the bacterial adhesion control, the modification of the material surface is the key for improving the performance of a device or even creating a completely new function. Among different laser processing techniques, Direct Laser Interference Patterning (DLIP) relies on the local surface modification process induced when two or more beams interfere and produce periodic surface structures. Although the produced features have controllable pitch and geometry, identical experimental conditions applied to different polymers can result on totally different topologies. In this frame, observations from pigmented and transparent polycarbonate treated with ultraviolet (263 nm) and infrared (1053 nm) laser radiation permitted to identify different phenomena related with the optical and chemical properties of the polymers. As a result from the experimental data analysis, a set of material-dependent constants can be obtained and both profile and surface simulations can be retrieved, reproducing the material surface topography after the surface patterning process.

Pulsed Laser Ablation in Liquids is an innovative method, which is used to obtain colloidal solutions of nanoparticles that show unique properties and are not achievable by conventional synthesis methods. However, this method lacks of key parameters and scaling factors as well as a correlation between these factors and the occurring operating costs.

During the laser driven synthesis cavitation bubbles filled with nanoparticles are formed. These cavitation bubbles along with already dispersed nanoparticles in the solution are the two major factors that limit the energy that can be coupled into the target material by shielding subsequent laser pulses. While the latter shielding effect can be avoided by suitable fluid handling avoiding the former is more difficult due to the lifetime (~100μs) and the size (~100μm) of cavitation bubbles which depend on the laser energy and pulse duration.

In this work we present a strategy to scale up the process by enhancing the productivity of the synthesis. This approach utilizes a MHz-repetition rate laser system consisting of a 500W ps-laser source and a laser scanner that reaches a scanning speed of up to 500m/s. This unique system enables spatial bypassing the cavitation bubble and thereby applying most of the laser energy to the target. By using this system productivities of up to 5 gram per hour are demonstrated in a continuous process.

For an industrial laser application, high process throughput and low average cost of ownership are critical to commercial success. Benefiting from high peak power, nonlinear absorption and small-achievable spot size, ultrafast lasers offer advantages of minimal heat affected zone, great taper and sidewall quality, and small via capability that exceeds the limits of their predecessors in via drilling for electronic packaging. In the past decade, ultrafast lasers have both grown in power and reduced in cost. For example, recently, disk and fiber technology have both shown stable operation in the 50W to 200W range, mostly at high repetition rate (beyond 500 kHz) that helps avoid detrimental nonlinear effects.

However, to effectively and efficiently scale the throughput with the fast-growing power capability of the ultrafast lasers while keeping the beneficial laser-material interactions is very challenging, mainly because of the bottleneck imposed by the inertia-related acceleration limit and servo gain bandwidth when only stages and galvanometers are being used. On the other side, inertia-free scanning solutions like acoustic optics and electronic optical deflectors have small scan field, and therefore not suitable for large-panel processing. Our recent system developments combine stages, galvanometers, and AODs into a coordinated tertiary architecture for high bandwidth and meanwhile large field beam positioning. Synchronized three-level movements allow extremely fast local speed and continuous motion over the whole stage travel range. We present the via drilling results from such ultrafast system with up to 3MHz pulse to pulse random access, enabling high quality low cost ultrafast machining with emerging high average power laser sources.

In the last decade much improvement has been achieved for ultra-short pulse lasers with high repetition rates. This laser technology has vastly matured so that it entered a manifold of industrial applications recently compared to mainly scientific use in the past. Compared to ns-pulse ablation ultra-short pulses in the ps- or even fs regime lead to still colder ablation and further reduced heat-affected zones. This is crucial for micro patterning when structure sizes are getting smaller and requirements are getting stronger at the same time. An additional advantage of ultra-fast processing is its applicability to a large variety of materials, e.g. metals and several high bandgap materials like glass and ceramics.

One challenge for ultra-fast micro machining is throughput. The operational capacity of these processes can be maximized by increasing the scan rate or the number of beams – parallel processing. This contribution focuses on process parallelism of ultra-short pulsed lasers with high repetition rate and individually addressable acousto-optical beam modulation. The core of the multi-beam generation is a smooth diffractive beam splitter component with high uniform spots and negligible loss, and a prismatic array compressor to match beam size and pitch. The optical design and the practical realization of an 8 beam processing head in combination with a high average power single mode ultra-short pulsed laser source are presented as well as the currently on-going and promising laboratory research and micro machining results. Finally, an outlook of scaling the processing head to several tens of beams is given.

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.

The material processing by two or more interfering laser beams, is referred to as Direct Laser Interference Patterning (DLIP). The periodic intensity pattern of the overlapping laser beams is used to ablate or modify the material so a functionalization of the surface is achieved. By adjusting the number, direction, intensity and polarization of the interfering beams, the detailed geometry of the intensity pattern can be shaped and the realizable feature sizes can be continuously adjusted within the micro- and submicrometer range. Consequently, the surface texture can be engineered and tailored to perfectly suit the needs of a given application.

Typical applications of DLIP range from in- and out coupling of light in solar cells or organic LEDs over improvement of tribological properties in engine parts to security markings and decoration applications due to the shimmering effect of the periodic textures. On laboratory scale, an improvement over unprocessed surfaces has been demonstrated in all of these mentioned applications. However, so far the feed rates have not sufficed to allow an industrial application of the technology.

Now, in a joint project of laser manufacturer, optics designer and engineering company, a machine platform has been developed which allows high surface processing speeds in an industrial environment. Feed rates in the range of square meters per minute (corresponding to about one billion features per second) can be achieved. With the help of this platform, DLIP can finally be lifted to industrial application.

Titanium alloys are generally noticed for their high specific strength and their good corrosion resistance. They are widely used in light-weight structures especially in the aerospace industry. Surface preparation of Ti6Al4V for bonding improvement is conventionally performed by chemical, electrochemical pre-treatments (chromic acid anodizing, phosphate-fluoride, sol-gel,…) and/or sandblasting in order to modify the morphology and the chemistry of the surface. However, these processes produce a large volume of hazardous chemical or abrasive waste. They require high technical efforts and are therefore economically and environmentally inefficient. Laser processes could lead to a good alternative solution in terms of eco-compatibility, repeatability and ease of manufacturing. In this paper, we report on the latest developments of the collaboration between ALPhANOV and I2M institute on the laser surface preparation for adhesive bonding improvement of Ti6Al4V. We focus our investigations on the effect of pulsed laser irradiation (fluence, scan speed and lateral overlap) with a visible (515 nm) nanosecond "rod-type fibre" laser on the surface morphology and its bonding behaviour (cohesive or adhesive failure). The penetration of the adhesive in the roughness induced by laser irradiation was characterized. For this study, the surfaces were inspected by different means as optical microscopy, 3D profilometer and scanning electron microscopy (SEM). The adhesion performance of the laser treated surface was evaluated by means of DCB tests.

Super-hydrophobic surfaces are nowadays of primary interest in several application fields, as for de-icing devices in the automotive and aerospace industries. In this context, laser surface texturing has widely demonstrated to be an easy one-step method to produce super-hydrophobic surfaces on several materials. In this work, a high average power (up to 40W), high repetition-rate (up to 1MHz), femtosecond infrared laser was employed to produce super-hydrophobic surfaces on 316L steel. The set of process and laser parameters for which the super-hydrophobic behavior is optimized, was obtained by varying the laser energy and repetition rate. The morphology of the textured surfaces was firstly analyzed by SEM and confocal microscope analyses. The contact angle was measured over time in order to investigate the effect of air environment on the hydrophobic properties and define the period of time necessary for the super-hydrophobic properties to stabilize. An investigation on the effect of after-processing cleaning solvents on the CA evolution was carried to assess the influence of the after-processing sample handling on the CA evaluation. Results show that the highest values of contact angle, that is the best hydrophobic behavior, are obtained at high repetition rate and low energy, this way opening up a promising scenario in terms of upscaling for reducing the overall process takt-time.

Experimental investigation of thermochemical laser-induced periodic surface structures (TLIPSS) formation on metal films (Ti, Cr, Ni, NiCr) at different processing conditions is presented. The hypothesis that the TLIPSS formation depends significantly on parabolic rate constant for oxide thin film growth is discussed. Evidently, low value of this parameter for Ni is the reason of TLIPSS absence on Ni and NiCr film with low Cr content. The effect of simultaneous ablative (with period ≈λ) and thermochemical (with period ≈λ) LIPSS formation was observed. The formation of structures after TLIPSS selective etching was demonstrated.

Pulsed laser ablation is a valuable tool that offers a much cleaner and more flexible etching process than conventional lithographic techniques. Although much research has been undertaken on commercially available polymers, many challenges still remain, including contamination by debris on the surface, a rough etched appearance and high ablation thresholds. Functionalizing polymers with a photosensitive group is a novel way and effective way to improve the efficiency of laser micromachining. In this study, several polyurethane films grafted with different concentrations of the chromophore anthracene have been synthesized which are specifically designed for 248 nm KrF excimer laser ablation. A series of lines etched with a changing number of pulses and fluences by the nanosecond laser were applied to each polyurethane film. The resultant ablation behaviours were studied through optical interference tomography and Scanning Electron Microscopy. The anthracene grafted polyurethanes showed a vast improvement in both edge quality and the presence of debris compared with the unmodified polyurethane. Under the same laser fluence and number of pulses the spots etched in the anthracene contained polyurethane show sharp depth profiles and smooth surfaces, whereas the spots etched in polyurethane without anthracene group grafted present rough cavities with debris according to the SEM images. The addition of a small amount of anthracene (1.47%) shows a reduction in ablation threshold from unmodified polyurethane showing that the desired effect can be achieved with very little modification to the polymer.

The surfaces of Ni50Ti50 shape memory alloys (SMAs) were patterned by laser scribing. This method is more simplistic and efficient than traditional indentation techniques, and has also shown to be an effective method in patterning these materials. Different laser energy densities ranging from 5 mJ/pulse to 56 mJ/pulse were used to observe recovery on SMA surface. The temperature dependent heat profiles of the NiTi surfaces after laser scribing at 56 mJ/pulse show the partially-recovered indents, which indicate a "shape memory effect (SME)" Experimental data is in good agreement with theoretical simulation of laser induced shock wave propagation inside NiTi SMAs. Stress wave closely followed the rise time of the laser pulse to its peak values and initial decay. Further investigations are underway to improve the SME such that the indents are recovered to a greater extent.

We propose a novel high aspect laser drilling technique for glass substrate assisted by supercritical CO₂ instead of water. Supercritical CO₂ has excellent solubility and fluidity, which facilitates efficient removal of ablated debris to the outside of the drilled hole. Thus, laser drilling using supercritical CO₂ results in deeper, thinner holes than those drilled using air and water. In experiments conducted, glass slab was placed in an enclosure filled with CO₂ around the critical point. Subsequently, a sub-picosecond pulsed laser focused and scanned on the sample created deeper and thinner holes with aspect ratios greater than 100.

Mg alloys are superior to other metallic biomaterials for temporary bio-application, owing to their biodegradability and biocompatibility features. However, the high reactivity and the rapid corrosion rate of Mg alloys are major barriers for their usage in bio-applications. In this paper, laser surface modification method is used to improve the surface properties of WE54. A 500 W pulse Nd: YAG laser beam is focused on the specimen through a 2 mm layer of simulated body fluid. As a result, a new microstructure and a Ca/P layer are obtained in a single process, which is conductive for the cell attachment.

The nanostructuring of dielectric surfaces using laser radiation is still a challenge. The IPSM-LIFE (laser-induced front side etching using in-situ pre-structured metal layer) method allows the easy, large area and fast laser nanostructuring of dielectrics. At IPSM-LIFE a metal covered dielectric is irradiated where the structuring is assisted by a self-organized molten metal layer deformation process. The IPSM-LIFE can be divided into two steps:

STEP 1: The irradiation of thin metal layers on dielectric surfaces results in a melting and nanostructuring process of the metal layer and partially of the dielectric surface.

STEP 2: A subsequent high laser fluence treatment of the metal nanostructures result in a structuring of the dielectric surface. At this study a sapphire substrate Al₂O₃(1-102) was covered with a 10 nm thin molybdenum layer and irradiated by an infrared laser with an adjustable time-dependent pulse form with a time resolution of 1 ns (wavelength λ = 1064 nm, pulse duration Δt_p = 1 – 600 ns, Gaussian beam profile). The laser treatment allows the fabrication of different surface structures into the sapphire surface due to a pattern transfer process. The resultant structures were investigated by scanning electron microscopy (SEM). The process was simulated and the simulation results were compared with experimental results.

In pulsed-laser micromachining, incubation refers to the chemical and structural change of a surface due to irradiation from a single pulse and the effect of this change on the absorption of the subsequent pulse. This ability to account for change in absorption properties of a surface – which is done through fitting of a single, material-dependent parameter – allows for prediction of the damage that will occur with irradiation and provides a pathway to uncover the complicated processes that govern incubation. However, the model as it currently stands only accounts for laser pulses irradiating a single spot on a surface. We develop, as a first step towards implementing incubation models for fabrication of surfaces with real-world applications, a mathematical description of the manner in which fluence accumulates during irradiation of surfaces moving with constant velocity relative to a beam. Within this description, we define the criteria for the accumulated fluence profile to be both fully-developed and flat and show that, when these criteria are met, the incubation models can be extended to moving surfaces. We demonstrate the necessity of such a framework with proof-of-concept experiments on three surfaces with distinct incubation behavior: glass, Titanium, and PET. Additionally, when the conditions of flat and fully-developed profile are relaxed, the cumulative and accumulated fluence profiles can differ continuously in the scanning direction. Comparison of real surfaces lased in this manner with their energy profiles can provide a new tool to further our understanding of the processes governing incubation.

The numerical modeling of light propagation based on Fresnel wavefront decomposition was performed. The reconstruction of a wavefront based on the direct superposition of Fresnel-Kirchhoff modifoed Greens functions was implemented. The high flexibility of possible initial conditions of simulation was applied for the calculation of holograms. The problems of fabrications of numerical simulated holograms was analyzed. The applicability of two-beam based material structuring equipment was analyzed. The method for decomposition of digital holograms into periodical two-beam interference pattern was researched. Based on this method, the group of producible holographic structures was found. The implementation of this model for numerical calculations of pattern decomposition was done. The transformation of estimated elements of decomposition was transformed into package of parameter for two-beam interference material structuring equipment.

Scalable methods must be developed for fabricating high-density arrays of conductive microchannels through ~0.5 mmthick synthetic diamonds in order to form radiation-hard 3D particle tracking detectors for use in future high-energy particle physics experiments, such as those beyond the scheduled 2022 high-luminosity upgrade of the Large Hadron Collider. Prototype detectors with small-area arrays of graphitic columns, each written by slowly translating a femtosecond laser beam focus through the diamond, have established proof of concept, but much faster procedures are needed to manufacture large arrays of electrodes with <100 micron spacing over diameters of ~10 cm. We have used a Bessel beam, formed using a 10° axicon and 0.68 NA aspheric lens, to very quickly write micron-diameter columns through ~0.5 mm-thick electronic grade CVD diamonds without axially translating the diamond with respect to the beam. We employ an optical microscope to visualize columns, Raman spectroscopy to ascertain the degree of graphitization, and cat-whisker probes to test overall conductivity. Bessel focusing enables formation of a complete column with just a few femtosecond laser pulses, and so provides a scalable manufacturing method. However, reduction in the electrode resistivity is desired. To this end, expulsion of material from the column is probably needed, as carbon plasma will otherwise condense back into diamond, due to the disparate densities of graphite and diamond. We describe the use of several different femtosecond laser systems to evaluate a range of pulse parameters with the goal of increasing the level of graphitization and improving the conductivity of the electrodes.

This paper focuses on femtosecond laser cutting and drilling using a patent pending technology for suppressing the conicity generated by the ablation saturation. We will show that a common scanning system can be used thanks to this technology with a conicity suppression on a scanning field of 20x20mm.

Publisher’s Note: This paper, originally published on February 17, 2017, was withdrawn per author request.

Ultrafast laser pulses can be used to achieve structuring of surfaces at the micro-nano scale. Under certain irradiation conditions, Laser Induced Periodic Surface Structures (LIPSS) are formed. The LIPSS dimensions range from 100 nm to 2-3 micrometers. The characterization is generally conducted after the laser irradiation by systems such as SEM and/or AFM with a resolution beyond the diffraction limit. In this paper, we use a super resolution microscopy technique based on structured illumination for in-situ observation of the irradiated surface. The LIPSS formation on steel and Si is observed IN-SITU and discussed for a multipulse sequence.

An advanced direct imprinting method with low cost, quick, and less environmental impact to create thermally controllable surface pattern using the laser pulses is reported. Patterned micro indents were generated on Ni₅₀Ti₅₀ shape memory alloys (SMA) using an Nd:YAG laser operating at 1064 nm combined with suitable transparent overlay, a sacrificial layer of graphite, and copper grid. Laser pulses at different energy densities which generates pressure pulses up to 10 GPa on the surface was focused through the confinement medium, ablating the copper grid to create plasma and transferring the grid pattern onto the NiTi surface. Scanning electron microscope (SEM) and optical microscope images of square pattern with different sizes were studied. One dimensional profile analysis shows that the depth of the patterned sample initially increase linearly with the laser energy until 125 mJ/pulse where the plasma further absorbs and reflects the laser beam. In addition, light the microscope image show that the surface of NiTi alloy was damaged due to the high power laser energy which removes the graphite layer.