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Ultrashort laser pulse micromachining features a high precision. By increasing the repetition rate of the applied laser to several 100 kHz, laser processing becomes quick and cost-effective and make
this method attractive for industrial applications. Upon exceeding a critical laser intensity, hard X-ray radiation is generated as a side effect. Even if the emitted X-ray dose per pulse is low, the accumulated X-ray dose becomes significant for high-repetition-rate laser systems so that radiation
safety must be considered.
Ultrashort laser pulse micromachining features a high precision. By increasing the repetition rate of the applied laser to several 100 kHz, laser processing becomes quick and cost-effective and make this method attractive for industrial applications. Upon exceeding a critical laser intensity, hard X-ray radiation is generated as a side effect. Even if the emitted X-ray dose per pulse is low, the accumulated X-ray dose becomes significant for high-repetition-rate laser systems so that radiation safety must be considered.
Unwanted X-ray emission in ultrashort pulse laser processing: From metallic to biological materials
(2023)
X-rays can be generated as an unwanted side effect during ultrashort pulse laser material processing of technical work pieces and even biological samples with laser intensities above 10^13 W/cm^2. First studies demonstrate the need to address this effect in industrial as well as in medical applications. This secondary hazard should be considered in work safety and risk assessment.
Die Reduktion von Reibung und Verschleiß in technischen Systemen bietet ein großes Potenzial zur Reduktion von CO2-Emissionen. Dieser Beitrag diskutiert die Erzeugung und tribologische Charakterisierung von Ultrakurzpuls-generierten Nano- und Mikrostrukturen auf Metallen (Stahl, Titan). Besonderes Augenmerk wird dabei auf die Rolle der laserinduzierten Oxidschicht im Zusammenspiel mit verschleißreduzierenden Additiven in ölbasierten Schmiermitteln gerichtet.
Long seen as “a solution seeking a problem,” laser pulses are nowadays – more than 60 years after their first practical demonstration – paramount in shaping and structuring matter. Harnessing their capabilities to direct intense beams of light, the number of scientific and technological developments and daily-life applications is continuously increasing. Today, the presence of lasers is ubiquitous in all sites of scientific and technological interest, from the most advanced research laboratories to industrial factories and medical hospitals.
The directionality of the laser beam determines equally a local character on lightmatter interaction and as such a local modification to a material target. Furthermore, the coherence of laser radiation enables near-field or far-field scattering and interference effects that widen significantly the capabilities of controlling and tracking laser-matter interactions in space and time. Already with the advent of lasers, powerful beams of light have been directed at solid materials for a variety of purposes, making this application as old as the laser itself. The roots of the major applications for laser structuring were developed already in the 1960s, setting the base of both theoretical and experimental studies on laser ablation, with the number of publications expanding explosively during the next decades.
Within this dynamic context, laser processing of materials experienced an impressive development over the years. Laser processing means specifically the capability to structure and tailor a material on its surface or even within its volume, rendering new functions and properties that are impacting the mechanical, electrical, or optical characteristics of the material. These properties are scaledependent, generating thus over the years an equally impressive quest for spatial or temporal resolution. Therefore, the developments in laser engineering with major breakthroughs, notably in pulse duration and power, always closely accompanied the efforts in material structuring with two milestones in sight: (1) yield and (2) resolution. Every step in shrinking the laser pulse duration led to a subsequent strong-impact development in process precision – particularly when the ultrashort pulse durations surpassed the fundamental electron-phonon relaxation times. Thus, minimizing heat diffusion, the advent of pulses with duration smaller than molecular or lattice vibration times has managed to confine the spatial resolution to the optical diffraction limit and sometimes even beyond. The nanoscale was already in sight at the turn of the millennium. An important question may be raised now; is there any fundamental limit in the processing resolution, a barrier defined by the intrinsic properties of light and matter? The answer has an inherently multidisciplinary nature, following the conversion of free-propagating electromagnetic radiation into
material-confined energy potentially usable to drive or transform matter, and will be the focus of the present book.
Relying on the experience and expertise of the leading researchers in the field, the present book intends to explore the current efforts in achieving laser processing resolution beyond the diffraction limit, laying down a perspective towards extreme laser nanostructuring. Following the most recent advances and developments, it puts forward a concept of extreme processing scales enabled by optical pulses that are able to bypass diffraction limits and achieve structuring characteristic scales beyond 100 nm. This objective can be achieved by a comprehensive understanding on how light can change matter and how, in turn, matter can change light, allowing jointly for actively controlling light and material processes. In order to give an extended perspective on the current state-of-the-art in the field of precision laser structuring, the book is divided into three main parts.
The first part of the book (Part I: Fundamental Processes) offers a perspective into the fundamentals of laser-matter interaction on extreme spatial scales, with a description of the most advanced modeling efforts in understanding energy deposition in matter, a plethora of material-relaxation pathways, as well as advanced concepts for probing and observing matter in motion. Roadmaps for energy localization will be developed, and the atomistic perspective of laser ablation visualized. Theoretical modelling enables in-depth insights on ultrafast quantum processes at the nanoscale. Laser-driven self-organization at surfaces will be dissected regarding the question of how light drives material periodic patterns down to the nanoscale, explored and transmitted to its ultimate limits of an atomic printer, and immediately complemented by the unprecedented capabilities of ultrafast in-situ observation approaches for tracking the laser-induced material response with extreme spatial and temporal resolution.
In the second part of the book (Part II: Concepts of Extreme Nanostructuring), distinct concepts will be developed and explored that allow confinement of light and harnessing of a material response restricted to nano- or mesoscopic scales at surfaces or in the volume of irradiated materials. A special focus will be on optical near-field related approaches for localizing light on scales even below the optical diffraction limit and plasmonic printing. Spatial and temporal beam-shaping and tailored interference techniques are discussed in the context of ultrashort laser pulses, and insights into some extreme states of matter realized by the tight confinement of laser energy are presented. The ultimate limits of writing waveguides in the bulk of dielectrics and for manifesting 3D-nanolithography are elucidated. Plasma-based surface treatments can significantly enhance the vertical precision of surface processing through etching processes.
Finally, the third part of the book (Part III: Applications) leads us to a number of resuming applications, unveiling the tremendous capabilities of surface functionalization through laser micro- and nanostructuring, assessing the 3D-writing of waveguides in the bulk of dielectrics or semiconductors for enabling new branches of integrated photonics, and summarizing related applications ranging from nanophotonics to nanofluidics and from optical sensing to biomedical applications, including the latest capabilities of refractive eye surgery. This part will analyze the applications’ compatibility in yield and reproducibility with current industrial requirements, costs, and intellectual property aspects. It expands the involved spatial scales by more than eight orders of magnitude, when extending extremely small structures featuring sizes of few tens of nanometers to larger dimensions in the meter range.
Thus, from surfaces to the bulk, from subtractive to additive manufacturing approaches, from advanced theoretical frames to practical technological processes – we invite the readers here to an exciting journey into the varicolored landscape of extreme laser nanostructuring.
The idea of this book project was seeded in early 2020. We were delighted about the numerous and extremely positive responses from the laser-processing community, quickly receiving commitments for more than 30 individual book chapters. About 2500 communications later, the book is published. We would like to thank all authors of this book project for their insightful and detailed chapters, reviewing and reporting on this fascinating topic of the pursuit of extreme scales in ultrafast laser nanostructuring. Moreover, we would like to acknowledge the professional help and guidance of the staff of Springer Nature. Finally, we hope you will enjoy reading this book as much as we have enjoyed putting it together.
Saint Etienne, France Razvan Stoian
Berlin, Germany Jörn Bonse
December 2022
Lasermaterialbearbeitung ist eine sich schnell entwickelnde Technologie, um eine Vielzahl von Oberflächenfunktionalitäten auf Basis optischer, mechanischer oder chemischer Eigenschaften zu realisieren. Die Verwendung ultrakurzer Laserimpulse mit Dauern im Femtosekundenbereich ermöglicht dabei neben einer herausragenden Bearbeitungs-präzision auch die selbstorganisierte Erzeugung verschiedener charakteristischer Ober-flächenstrukturen mit Größenskalen im Mikrometer- bis hinunter in den sub-100-nm-Bereich, z.B. sogenannte Ripples („Laser-Induced Periodic Surface Structures“, LIPSS), Grooves, oder Spikes.
In dem Vortrag wird ein Überblick über die in den vergangenen Jahren in Zusammenarbeit mit dem BAM Fachbereich 6.3 durchgeführten tribologischen Experimente gegeben. Besonderes Augenmerk liegt dabei auf den tribologischen Eigenschaften (Reibung und Verschleiß) der unterschiedlichen Femtosekunden-Laser-generierten Oberflächen-morphologien auf gängigen Metallen (z.B. Stahl, Titan). Einflüsse durch die Veränderungen der Härte des Werkstoffs infolge Laser-induzierter Oxidation, der Dicke und Struktur der Oxidschicht, und die Wirksamkeit unterschiedlicher Schmiermittel (z.B. additiviertes Motoröl) werden diskutiert.
Laser-induced periodic surface structures (LIPSS, ripples) were generated on steel and titanium surfaces upon irradiation with multiple linear polarized femtosecond laser pulses (pulse duration 30 fs, central wavelength 790 nm). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning geometry for the processing of large surface areas covered homogeneously by the nanostructures. The irradiated surface regions were subjected to optical microscopy (OM), white light interference microscopy (WLIM) and scanning electron microscopy (SEM) revealing sub-wavelength spatial periods. The nanostructured surfaces were tribologically tested under reciprocal sliding conditions against a sphere of hardened 100Cr6 steel at 1 Hz using paraffin oil and engine oil as lubricants. After 1000 sliding cycles at a load of 1.0 N, the corresponding wear tracks were characterized by OM and SEM. For specific conditions the laser-generated nanostructures endured the tribological treatment. Simultaneously, a significant reduction of the friction coefficient was observed in the laser-irradiated (LIPSS-covered) areas when compared to the non-irradiated surface, indicating the potential benefit of laser surface structuring for tribological applications.
Commercial grade-1 titanium samples (Ti, 99.5% purity) were treated using three alternative methods, i.e., fs-laser processing in air, thermal heat treatment in an oven, or anodization in an electrochemical bath, all resulting in the formation of differently conditioned superficial oxide layers. The laser processing was carried out by a Ti:sapphire laser (pulse duration 30 fs, central wavelength 790 nm, pulse repetition rate 1 kHz) in a regime of generating laser-induced periodic surface structures (LIPSS). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning geometry for the processing of several square-millimetres large surface areas covered homogeneously by these nanostructures. The thermal processing in the oven was done at two different temperatures, while the electrochemical anodization was performed at room temperature, aiming to generate different polymorphs of titanium oxide at similar oxide layer thickness. The irradiated surface regions were characterized by optical and scanning electron microscopy, and micro Raman spectroscopy. The tribological performance of the differently treated titanium surfaces was characterized in the regime of mixed friction by reciprocating sliding tests against a sphere of hardened steel in un-additivated paraffin oil and fully formulated engine oil as lubricants. The specific tribological performance of the differently treated surfaces is discussed on the basis of possible physical and chemical mechanisms.
Tribological performance of femtosecond laser-induced periodic surface structures on titanium
(2015)
Towards an industrial laser doping process for the selective emitter using phosphoric acid as dopant
(2011)
Different laser supported approaches have already been realized, proving the great potential of laserdoped selective emitters (LDSE). However, it is challenging to establish a low-cost process by using pulsed laser tools. So far a single-step process only leads to satisfying results utilizing cw-lasers. In this paper we have examined a two-step process to produce laser-doped selective emitters on multicrystalline textured standard silicon photovoltaic wafers (90-Ω/sq-Emitter, SiN-antireflection coating (ARC)). The precise ARC removal by near-infrared fs-laser pulses (30 fs, 800 nm), and the doping of uncoated silicon wafers by ns-laser pulses (8 ns, 532 nm) were systematically investigated. In the fs-experiment, optimum conditions for ARC removal were identified. In the nsexperiments under suitable conditions (melting regime), the phosphorous concentration underneath the wafer surface was significantly increased and the sheet resistance was reduced by nearly a factor of two. Moreover, electrical measurements on fired metallization fingers deposited on the laser processed wafers showed low contact resistances. Hence, wafer conditioning with combined fs-laser- and ns-laser-processes are expected to be a promising technology for producing selective emitters.
Ultrashort pulses lasers are tools of choice for functionalizing the bulk of transparent materials. In particular, direct photoinscription of simple photonic functions have been demonstrated. Those elementary functions rely on the local refractive index change induced when focusing an ultrashort pulse in the volume of a transparent material. The range of possibilities offered by direct photoinscription is still under investigation. To help understanding, optimizing and assessing the full potential of this method, we developed a time-resolved phase contrast microscopy setup. The imaginary part (absorption) and the real part of the laser-induced complex refractive index can be visualized in the irradiated region. The setup is based on a commercially available phase contrast microscope extended into a pump-probe scheme. The originality of our approach is that the illumination is performed by using a pulsed laser source (i.e. a probe beam). Speckle-related issues are solved by employing adequate sets of diffusers. This laser-microscopy technique has a spatial resolution of 650 nm, and the impulse response is about 300 fs. The laser-induced refractive index changes can be tracked up to milliseconds after the energy deposition. The excitation beam (the pump) is focused with a microscope objective (numerical aperture of 0.45) into the bulk of an a-SiO2 sample. The pump beam can be temporally shaped with a SLM-based pulse shaping unit. This additional degree of flexibility allows for observing different interaction regimes. For instance, bulk material processing with femtosecond and picosecond duration pulses will be studied.
Laser-induced periodic surface structures (LIPSS) are a universal phenomenon that is accompanying laser materials processing. These surface nanostructures pave a simple way for surface functionalization with numerous applications in optics, fluidics, tribology, medicine, etc. This contribution reviews the current view on the role of electromagnetic scattering in the formation of LIPSS.
The role of electromagnetic scattering in the formation of laser-induced periodic surface structures
(2021)
Laser-induced periodic surface structures (LIPSS) are a universal phenomenon that is accompanying laser materials processing. These surface nanostructures pave a simple way for surface functionalization with numerous applications in optics, fluidics, tribology, medicine, etc. During the last decade remarkable experimental and theoretical improvements in understanding of their formation mechanisms were obtained - all pointing toward polarization-dependent energy deposition by absorption of optical radiation that is scattered at the surface roughness and interfering with the laser beam. This contribution reviews the current state-of-the-art on the role of electromagnetic scattering in the formation of LIPSS by ultrashort laser pulses. Special attention is drawn to recent finite-difference time-domain (FDTD) calculations that allow to visualize the radiation patterns formed in the vicinity of the sample surface and to the impact of a thin superficial laser-induced oxidation layer.
Different types of laser-generated surface structures, i.e., Laser-induced Periodic Surface Structures (LIPSS, ripples), Grooves, and Spikes are generated on titanium and Ti6Al4V surfaces by means of femtosecond (fs) laser scan processing (790 nm, 30 fs, 1 kHz) in ambient air. Morphological, chemical and structural properties of the different surface structures are characterized by various surface analytical techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), Glow discharge optical emission spectroscopy (GD-OES), and depth-profiling Auger electron spectroscopy (AES). It is revealed that the formation of near-wavelength sized LIPSS is accompanied by the formation of a graded oxide extending several tens to a few hundreds of nanometers into depth. GD-OES performed on other superficial fs-laser generated structures produced at higher fluences and effective number of pulses per spot area such as periodic Grooves and irregular Spikes indicate even thicker graded oxide layers. These graded layers may be suitable for applications in prosthetics or tribology.
The presentation reviews the BAM activities in the field of surface processing by ultrashort laser pulses. A focus is laid on the generation of laser-induced periodic surface structures (LIPSS) which allow various surface functionalizations for applications in optics, tribology, liquid management, and medicine.
In this contribution the mechanisms of formation and current applications of LIPSS are reviewed, including the colorization of technical surfaces, the control of surface wetting properties, the mimicry of the natural texture of animal integuments, the tailoring of surface colonization by bacterial biofilms, and the improvement of the tribological performance of nanostructured metal surfaces.
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 femtosecond to picosecond 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, biological, or chemical surface properties. In this contribution the mechanisms of formation and current applications of LIPSS are reviewed, including the colorization of technical surfaces, the control of surface wetting properties, the mimicry of the natural texture of animal integuments, the tailoring of surface colonization by bacterial biofilms, the advancement of medical pacemakers, and the improvement of the tribological performance of nanostructured metal surfaces.
In recent years, the improved understanding of the formation of laser-induced periodic surface structures (LIPSS) has led to an emerging variety of applications that modify the optical, mechanical and chemical properties of many materials. Such structures strongly depend on the laser beam polarization and are formed usually after irradiation with ultrashort linearly polarized laser pulses. The most accepted explanation for the origin of the structures is based on the interference of the incident laser radiation with electromagnetic surface waves that propagate or scatter at the surface of the irradiated materials. This leads to an intensity modulation that is finally responsible for the selective ablation in the form of parallel structures with periods ranging from hundreds of nanometers up to some micrometers. The versatility when forming such structures is based on the high reproducibility with different wavelength, pulse duration and repetition rate laser sources, customized micro- and nanometric spatial resolutions, and the compatibility with industrially relevant processing speeds when combined with fast scanning devices. In this contribution, we review the latest applications in the rapidly emerging field of surface functionalization through LIPSS, including biomimetic functionalities on fluid transport, control of the wetting properties, specific optical responses in technical materials, improvement of tribological performance on metallic surfaces and bacterial and cell growth for medical devices, among many others.
Structural phenomena in multicomponent silicate glasses after femtosecond laser pulse irradiation
(2014)
Structural and morphological modifikation of crystalline silicon induced femtosecond laser pulses
(2010)
XUV- and X-ray free-electron-lasers (FEL) combine short wavelength, ultrashort pulse duration, spatial coherence and high intensity. This unique combination of properties opens up new possibilities to study the dynamics of non-reversible phenomena with ultrafast temporal and nano- to atomic-scale spatial resolution. In this contribution we wish to present results of time-resolved experiments performed at the XUV-FEL FLASH (HASYLAB/Hamburg) aimed to investigate the nano-scale structural dynamics of laser-irradiated materials. Thin films and fabricated nano-structures, deposited on Si3N4-membranes, have been excited with ultrashort optical laser pulses. The dynamics of the non-reversible structural evolution of the irradiated samples during laser-induced melting and ablation has been studied in an optical pump - XUV-probe configuration by means of single-shot coherent scattering techniques (i.e. diffraction imaging [1]). In a first set of experiments we investigated the formation of laser induced periodic surface structures (LIPSS) on the surface of thin Si-films (thickness 100 nm). In a simplified view LIPPS are generated as a result of interference between the incident laser pulse and surface scattered waves which leads to a periodically modulated energy deposition. Time-resolved scattering using femtosecond XUV-pulses (with a wavelength of 13.5 nm and 7 nm) allowed us to directly follow LIPSS evolution on an ultrafast time-scale and with better than 40 nm spatial resolution. The observed scattering patterns show almost quantitative agreement with theoretical predictions [2] and reveal that the LIPSS start to form already during the 12 ps pump pulse. In the second set of measurements we studied picosecond and femtosecond laser induced ablation and disintegration of fabricated nano-structures. Correlations of coherent diffraction patterns measured at various time delays to the pattern of the undisturbed object show that order in the structure is progressively lost starting from short length scales. This structural rearrangement progresses at close to the speed of sound in the material. Under certain circumstances (e.g. adequate sampling) it became also possible to reconstruct real-space images of the object as it evolves over time [3]. The possibility of femtosecond single-shot imaging of ultrafast dynamic processes with nanoscale resolution provides yet more details of the physical processes involved. [1] H. N. Chapman et al. Nature Phys. 2, 839 (2006). [2] J. F. Young et al., Phys. Rev. B 27, 1155 (1983). [3] A. Barty et al. Nature Phot. 2, 415 (2008).
Short-pulse laser induced melting and ablation studied with time-resolved coherent XUV scattering
(2010)
Laser ablation of single-crystalline indium phosphide (InP) was performed in air by means of linearly polarized Ti:sapphire femtosecond-pulses (800 nm, 130 fs, 10 Hz). As a result of the first laser pulses, several morphological changes (crater formation, rim formation, ripple structures and cones) were observed. These effects were explored using force modulation microscopy (FMM), a technique based on scanning force microscopy (SFM), allowing the simultaneous imaging of both topography and local stiffness at a high lateral resolution. The first laser pulse induces the formation of a protruding rim (height <20 nm, width ~300 nm) bordering the ablated crater. A Fourier-analysis of the multi-pulse generated topographies reveals the formation of wavelength-sized periodic ripples (modulation depth <100 nm) with an orientation perpendicular to that of the electric field vector of the laser radiation. Besides these morphological alterations, also material modifications were observed in the irradiated regions by means of the FFM technique. Within the ablated craters, local stiffness variations were found revealing an inhomogeneous material composition/structure as a consequence of the femtosecond pulse laser treatment.
In this work, glasses with systematically varied compositions were manufactured and irradiated by single Ti:sapphire fs-laserpulses (800 nm, 120 fs), focused at the surface and into the bulk of the glass materials. The samples were tested for their ablation threshold fluence as well as for structural changes using µ-Raman-spectroscopy. Correlations between the glass composition, the material-ablation on the glass surface and the permanent changes of the refractive index inside the glass volume after the irradiation by fs-laser pulses were obtained. The results show, that the structural modifications found at the surface of the glasses and inside its volume are closely related. However, while the ablation threshold fluence of the glass surface primarily depends on the glass dissociation energy, the permanent refractive index change inside the volume is rather determined by its ability for absorbing the fs-laser pulses and the subsequent relaxation processes. The results of this work provide some guidance on how the glass composition can be varied in order to optimize the fs-laser induced modification of dielectrics.
The invention of new miniaturized and smart medical implants continues in all medical fields, including miniaturized heart pacemakers. These implants often come with a titanium (Ti) casing, which may have to be removed after several months or years and shall therefore not be completely overgrown by cells or scar tissue after implantation. Scar tissue is mainly formed by fibroblast cells and extracellular matrix proteins like collagen produced by them. Suppression of fibroblast growth at Ti surfaces could be achieved by 800 nm femtosecond laser-ablation creating self-organized sharp spikes with dimensions in the 10 μm-range which are superposed by fine sub-μm parallel ripples. On flat Ti control samples, the best results regarding suppression of cell growth were obtained on spike-structures which were additionally electrochemically anodized under acidic conditions. When Ti cylinders with a diameter of 8 mm (similar as the pacemakers) were placed upright in a culture of murine fibroblasts, a multi-layer cell growth up to a height of at least 1.5 mm occurred within 19–22 days. We have demonstrated that a laser-structured and anodized ring around the Ti cylinder surface is an effective way to create a barrier that murine fibroblasts were not able to overgrow within this time.
This presentation reviews current and expected developments in the field of laser-induced periodic surface structures (LIPSS, ripples). These surface nanostructures are a universal phenomenon and can be generated on almost any material by irradiation with intense linearly polarized radiation. LIPSS are formed in a “self-ordered” way and are often accompanying laser material processing applications. The structures can be produced in a single-step process and enable surface functionalization through the adaption of optical, mechanical and chemical surface properties. Their spatial periods typically range from several micrometers down to less than 100 nanometers, exhibiting a clear correlation with the polarization direction of the laser radiation used. Various types of LIPSS have been classified, relevant control parameters were identified, and material specific formation mechanisms are analyzed for different types of inorganic solids, i.e., metals, semiconductors, and dielectrics, through time-resolved optical experiments and theoretical simulations. Special attention will be paid to a comparison of the currently available formation theories for LIPSS with a discussion of their respective strengths and weaknesses. Currrently explored applications featuring surface functionalization in the fields of optics, surface wetting, medicine, and tribology will be discussed.
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 femtosecond to picosecond range. During the past years significantly increasing industrial and 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 surface properties. In this contribution the mechanisms of formation and current trends and applications of LIPSS are reviewed, including the colorization of technical surfaces, the control of surface wetting properties, the mimicry of the natural texture of animals, the tailoring of surface colonization by bacterial biofilms, the advancement of leadless medical pacemakers, and the improvement of the tribological performance of nanostructured metal surfaces.
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 femtosecond to picosecond range. During the past years significantly increasing industrial and 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, biological, or chemical surface properties. In this contribution the mechanisms of formation and current trends and applications of LIPSS are reviewed, including the colorization of technical surfaces, the control of surface wetting properties, the mimicry of the natural texture of animals, the tailoring of surface colonization by bacterial biofilms, the advancement of leadless medical pacemakers, and the improvement of the tribological performance of nanostructured metal surfaces.
Over the past years, many applications based on laser-induced refractive index changes in the volume of transparent materials have been demonstrated. Ultrashort pulse lasers offer the possibility to process bulky transparent materials in three dimensions, suggesting that direct laser writing will play a decisive role in the development of integrated micro-optics. At the present time, applications such as 3D long term data storage or embedded laser marking are already into the phase of industrial development. However, a quantitative estimate of the laser-induced refractive index change is still very challenging to obtain. On another hand, several microscopy techniques have been recently developed to characterize bulk refractive index changes in-situ. They have been mostly applied to biological purposes. Among those, spatial light interference microscopy (SLIM), offers a very good robustness with minimal post acquisition data processing. In this paper, we report on using SLIM to measure fs-laser induced refractive index changes in different common glassy materials, such as fused silica and borofloat glass (B33). The advantages of SLIM over classical phase-contrast microscopy are discussed.
Antibiotic resistance is a growing global problem which poses a massive threat to human health. Although human activity contributes to the acceleration of the process, bacteria have a self-driven stabilisation mechanism to protect themselves from such and other external threats: biofilm formation. Nonetheless, it is the adhesion of a single bacterial cell to a surface that triggers the formation of such network of biomolecules and microorganisms, as well as its hazardous consequences. The main objective of this work was to quantify the adhesion force of a single E. coli cell on a Ti substrate via the AFM-related single-cell force spectroscopy, with both the cell and the substrate material being of high clinical relevance. A set of 25 x 25 force displacement curves was acquired with a maximum force of 3.2 nN without dwell time, yielding a topography map and an adhesion force map that showed to be correlated. A mean adhesion force of 0.85 ± 0.175 nN was measured and the presence of cell appendages on the bacterial cell wall was verified through individual force-displacement curves. Bacterial viability was assessed after the measurements via live/dead staining.
Irradiation of solid surfaces with intense ultrashort laser pulses represents a unique way of depositing energy into materials. It allows to realize states of extreme electronic excitation and/or very high temperature and pressure and to drive materials close to and beyond fundamental stability limits. As a consequence, structural changes and phase transitions often occur along unusual pathways and under strongly nonequilibrium conditions. Due to the inherent multiscale nature — both temporally and spatially—of these irreversible processes, their direct experimental observation requires techniques that combine high temporal resolution with the appropriate spatial resolution and the capability to obtain good quality data on a single pulse/event basis. In this respect, fourth-generation light sources, namely, short wavelength and short pulse free electron lasers (FELs), are offering new and fascinating possibilities. As an example, this talk will discuss the results of scattering experiments carried out at the FLASH free electron laser at DESY (Hamburg, Germany), which allowed us to resolve laser-induced structure formation at surfaces on the nanometer to submicron length scale and in temporal regimes ranging from picoseconds to several nanoseconds with sub-picosecond resolution. The current status and future perspectives in this field via exploiting the unique possibilities of these 4th-generation light sources will be discussed.
Manufacturing of CIGSe thin film solar modules involves typically one laser structuring step (P1) and two mechanical structuring steps (P2 and P3) for serial interconnection. In our approach, complete laser structuring is successfully demonstrated by application of short nanosecond laser pulses (<10 ns) with a single, visible wavelength of 532 nm. The P1 and the P3 trenches are scribed by induced and direct ablation, respectively. For the P2 scribe, the thermal input of the ns laser pulses is used to transform the CIGSe absorber layer locally into a highly conductive compound to provide proper electrical interconnection. These findings promise further simplification and flexibility to thin film solar cell production.
One wavelength fits all
(2011)
Structuring of Thin-film Solar Cells with a Single Laser Wavelength Structuring of a PV module into a number of cells is necessary to lower the current and to increase the voltage, and is typically accomplished with nanosecond laser pulses of different wavelengths. Duetothe many available laser sources, complex and expensive scribing Setups are necessary. To overcome this a concept for laser structuring of thin-film PV modules using a single wavelength allows prediction ofthe ablation behaviourfor a given laser pulse energy.
Laser-induced periodic surface structures (LIPSS, ripples) with ~500–700 nm period were produced on titanium alloy (Ti6Al4V) surfaces upon scan processing in air by a Ti:sapphire femtosecond laser. The tribological performance of the surfaces were qualified in linear reciprocating sliding tribological tests against balls made of different materials using different oilbased lubricants. Extending our previous work, we studied the admixture of the additive 2-ethylhexyl-zinc-dithiophosphate to a base oil containing only anti-oxidants and temperature stabilizers. The presence of this additive along with the variation of the chemical composition of the counterbodies allows us to explore the synergy of the additive with the laseroxidized nanostructures.
Ein wesentlicher Vorteil der Dünnschichtphotovoltaik gegenüber der waferbasierten Photovoltaik liegt in der monolithischen Serienverschaltung. Bei der Herstellung von Chalkopyrit(CIGSe) -Dünnschicht-Solarmodulen erfolgen dafür typischerweise ein Laser-Strukturierungsschritt (P1) und zwei mechanische Strukturierungsschritte (P2, P3). In diesem Beitrag wird gezeigt, dass die Strukturierung von CIGSe-Solarmodulen vollständig mit kurzen Laserpulsen (<10 ns Pulsdauer) und einer einzigen Wellenlänge (532 nm) möglich ist. Der P1- und P3-Schnitt erfolgen durch direkte induzierte Ablation. Für den P2-Schnitt wird gezielt der hohe Wärmeeintrag der ns-Laserpulse genutzt, um die CIGSe-
Absorberschicht lokal aufzuschmelzen und strukturell so zu verändern, dass eine elektrisch gut leitende Verbindung zwischen Front- und Rückkontakt entsteht.