TY - JOUR A1 - Kraft, Sebastian A1 - Schille, J. A1 - Bonse, Jörn A1 - Löschner, U. A1 - Krüger, Jörg T1 - X‑ray emission during the ablative processing of biological materials by ultrashort laser pulses N2 - The ablative laser processing with ultrashort pulsed laser beams may cause secondary emission of hazardous X-rays. While the effect has recently been proven to be considered in working safety regulations when processing technical materials, such as metals, the X-ray emission rates during the ablative processing of biological tissue materials are widely unexplored yet. Therefore, biological materials like water, isotonic saline solution, pig eyes, and human teeth were ablated with ultrashort laser pulses of 1030 nm wavelength, 600 fs pulse duration and 5 kHz pulse repetition rate, aiming to mimic typical surgery situations. Simultaneously, in-situ X-ray dose rate measurements were performed at a short distance from the plasma to display potential X-ray emission. For all four studied biological materials, our measurements prove the secondary emission of laser-induced X-rays. KW - Ultrashort pulsed laser KW - Laser-induced X-ray emission KW - Ophthalmology KW - Dentistry KW - Secondary hazard PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-569960 DO - https://doi.org/10.1007/s00339-023-06440-4 SN - 0947-8396 VL - 129 IS - 3 SP - 1 EP - 8 PB - Springer AN - OPUS4-56996 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Legall, Herbert A1 - Schwanke, Christoph A1 - Bonse, Jörn A1 - Krüger, Jörg T1 - X-ray radiation protection aspects during ultrashort laser processing N2 - Ultrashort pulse laser processing of materials allows for precise machining with high accuracy. By increasing the repetition rate to several 100 kHz, laser machining becomes quick and cost-effective. Ultrafast laser processing at high repetition rates and peak intensities above 10^13 W/cm^2 can cause a potential hazard by generation of unwanted x-ray radiation. Therefore, radiation protection must be considered. For 925 fs pulse duration at a center wavelength of 1030 nm, the x-ray emission in air at a repetition rate of 400 kHz was investigated up to a peak intensity of 2.6 × 10^14 W/cm^2. Based on the presented measurements, the properties of potential shielding materials will be discussed. By extending our previous works, a scaling of the x-ray radiation emission to higher peak intensities up to 10^15 W/cm^2 is described, and emitted x-ray doses are predicted. KW - Laser ablation KW - Ultrashort pulse laser processing KW - Laser-induced x-ray emission KW - Radiation protection PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-505677 DO - https://doi.org/10.2351/1.5134778 VL - 32 IS - 2 SP - 022004 AN - OPUS4-50567 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stolzenberg, U. A1 - Schmitt Rahner, M. A1 - Pullner, B. A1 - Legall, Herbert A1 - Bonse, Jörn A1 - Kluge, M. A1 - Ortner, A. A1 - Hoppe, B. A1 - Krüger, Jörg T1 - X-ray emission hazards from ultrashort pulsed laser material processing in an industrial setting N2 - Interactions between ultrashort laser pulses with intensities larger than 10^13 W/cm^2 and solids during material processing can lead to the emission of X-rays with photon energies above 5 keV, causing radiation hazards to operators. A framework for inspecting X-ray emission hazards during laser material processing has yet to be developed. One requirement for conducting radiation protection inspections is using a reference scenario, i.e., laser settings and process parameters that will lead to an almost constant and high level of X-ray emissions. To study the feasibility of setting up a reference scenario in practice, ambient dose rates and photon energies were measured using traceable measurement equipment in an industrial setting at SCHOTT AG. Ultrashort pulsed (USP) lasers with a maximum average power of 220 W provided the opportunity to measure X-ray emissions at laser peak intensities of up to 3.3 × 10^15 W/cm^2 at pulse durations of ~1 ps. The results indicate that increasing the laser peak intensity is insufficient to generate high dose rates. The investigations were affected by various constraints which prevented measuring high ambient dose rates. In this work, a list of issues which may be encountered when performing measurements at USP-laser machines in industrial settings is identified. KW - X-ray emission hazards KW - Ultrashort pulsed laser KW - Radiation protection KW - Industrial applications KW - Protection housing PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-538632 DO - https://doi.org/10.3390/ma14237163 SN - 1996-1944 VL - 14 SP - 1 EP - 17 PB - MDPI CY - Basel AN - OPUS4-53863 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Böttcher, Katrin A1 - Kraft, Sebastian A1 - Weise, Matthias A1 - Bonse, Jörn A1 - Krüger, Jörg T1 - X-ray emission during ultrafast laser grooving N2 - Ultrashort pulse lasers offer the possibility to process materials with minimal heat input and high precision. However, the X-ray emission at high laser peak intensities represents an undesirable side effect. A laser system (1030 nm wavelength, 40 W maximum average laser power, 925 fs pulse duration, 100 μJ maximum pulse energy, 400 kHz pulse repetition frequency) was used to analyze the X-ray skin dose rates for applied peak intensities between 9.2 × 10^12 W/cm^2 and 1.3 × 10^14 W/cm^2 for mild steel, stainless steel and tungsten during groove processing. The lowest laser peak intensity at which X-ray emission could be measured was 9.2 × 10^12 W/cm^2 for processing of stainless steel. The X-ray emission showed a characteristic evolution in dependence on the number of overscans at the same line positions. For low peak intensities, a measurable X-ray emission only begins after a few passes. The number of scans to reach the maximum dose rate increases with lower laser peak intensity. Analysis of the evolving surface topography by white light interference microscopy in connection with ray-tracing simulations led to the interpretation that the increase in X-ray emission is due to the local intensity redistribution by multiple reflection within the laser-generated grooves which is promoted by a particular choice of the linear laser polarization. KW - Ultrashort pulsed laser KW - Laser-induced X-rays KW - X-ray hazard KW - X-ray emission PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-639483 DO - https://doi.org/10.1007/s00339-025-08728-z SN - 1432-0630 VL - 131 IS - 8 SP - 1 EP - 12 PB - Springer CY - Berlin AN - OPUS4-63948 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Böttcher, Katrin A1 - Schmitt Rahner, M. A1 - Stolzenberg, U. A1 - Kraft, Sebastian A1 - Bonse, Jörn A1 - Feist, C. A1 - Albrecht, D. A1 - Pullner, B. A1 - Krüger, Jörg T1 - Worst-case X-ray photon energies in ultrashort pulse laser processing N2 - Ultrashort pulse laser processing can result in the secondary generation of unwanted X-rays if a critical laser irradiance of about 10^13 W/cm^2 is exceeded. Spectral X-ray emissions were investigated during the processing of tungsten and steel using three complementary spectrometers (based on CdTe and silicon drift detectors) simultaneously for the identification of a worst-case spectral scenario. Therefore, maximum X-ray photon energies were determined, and corresponding dose equivalent rates were calculated. An ultrashort pulse laser workstation with a pulse duration of 274 fs, a center wavelength of 1030 nm, pulse repetition rates between 50 kHz and 200 kHz, and a Gaussian laser beam focused to a spot diameter of 33 µm was employed in a single pulse and burst laser operation mode. Different combinations of laser pulse energy and repetition rate were utilized, keeping the average laser power constant close to the maximum power of 20 W. Peak irradiances ranging from 7.3 × 10^13 W/cm^2 up to 3.0 × 10^14 W/cm^2 were used. The X-ray dose equivalent rate increases for lower repetition rates and higher pulse energy if a constant average power is used. Laser processing with burst mode significantly increases the dose rates and the X-ray photon energies. A maximum X-ray photon energy of about 40 keV was observed for burst mode processing of tungsten with a repetition rate of 50 kHz and a peak irradiance of 3 × 10^14 W/cm^2. KW - Ultrashort pulsed laser KW - X-ray emission KW - X-ray spectrum KW - X-ray energies KW - Radiation protection PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-566176 DO - https://doi.org/10.3390/ma15248996 VL - 15 IS - 24 SP - 1 EP - 17 PB - MDPI AN - OPUS4-56617 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Hülagü, Deniz A1 - Hirahara, Kenta A1 - Fischer, Daniel A1 - Florian, Camilo A1 - Schusterbauer, Robert A1 - Ermilova, Elena A1 - Krüger, Jörg A1 - Unterreiner, Andreas-Neil A1 - Bonse, Jörn A1 - Hertwig, Andreas T1 - Using imaging ellipsometry to understand femtosecond laser materials processing of group IV materials N2 - Laser materials processing is an important tool for creating and shaping new materials. Laser machining, especially with ultrashort pulses offers the modification of surfaces, thin coatings, and bulk materials with an unprecedented precision and control. The most desired feature of pulsed laser processing in the femtosecond range is that the heat-affected zone in the irradiated material will be extremely small. To better understand the mechanisms involved during laser irradiation, it is important to analyse the outcome of light-matter interaction with spectroscopic methods. Ellipsometry, especially spectroscopic imaging ellipsometry (SIE), has become an important tool for this in recent times, as it gives access to local layer thicknesses, materials dielectric functions, and features like changes in surface roughness. This work includes an overview over our recent studies examining near-infrared fs-laser surface processing of different group IV materials. The superficial phase change of silicon from crystalline to amorphous has been investigated in the past as the result of laser processing strongly depends on the crystal orientation. Moreover, SIE is capable of determining the properties of buried a-Si interfaces with micrometer lateral and sub-nanoneter vertical precision. Additionally, the growth of native and laser-induced oxides can be revealed. T2 - ICSE10 - 10th International Conference on Spectroscopic Ellipsometry CY - Boulder, CO, USA DA - 08.06.2025 KW - Laser surface ablation KW - Amorphous Carbon KW - Silicon KW - Correlative Imaging Ellipsometry PY - 2025 AN - OPUS4-63633 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kraft, S. A1 - Böttcher, Katrin A1 - Bonse, Jörn A1 - Schille, J. A1 - Löschner, U. A1 - Krüger, Jörg T1 - Unwanted X-ray emission in ultrashort pulse laser processing: From metallic to biological materials N2 - 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. T2 - Lasers in Manufacturing 2023 (LiM 2023) CY - Munich, Germany DA - 26.06.2023 KW - Ultrashort pulse laser processing KW - Laser-induced X-ray emission KW - Secondary hazard PY - 2023 SP - LiM 2023 - 1 EP - LiM 2023 - 6 PB - Wissenschaftliche Gesellschaft Lasertechnik und Photonik e.V. (WLT) AN - OPUS4-58358 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bonse, Jörn T1 - Ultrafast optical probing of laser-induced formation of periodic surface nanostructures N2 - Laser-induced Periodic Surface Structures (LIPSS, ripples) are a universal phenomenon and can be generated in a contactless, single-step process on almost any type of solid upon irradiation with intense laser pulses. They represent a (quasi-)periodic modulation of the surface topography in the form of a linear grating and are typically formed in a “self-ordered” way in the focus of a coherent laser beam. Thus, they are often accompanying laser material processing applications. The structural sizes of LIPSS typically range from several micrometers down to less than 100 nanometers – far beyond the optical diffraction limit – while their orientations exhibit a clear correlation with the local polarization direction of the laser radiation. From a theoretical point of view, a controversial debate has emerged during the last decades, whether LIPSS originate from electromagnetic effects (seeded already during the laser irradiation) – or whether they emerge from matter-reorganization processes (distinctly after the laser irradiation). From a practical point of view, however, LIPSS represent a simple and robust way for the nanostructuring of solids that allows creating a wide range of different surface functionalities featuring applications in optics, tribology, medicine, energy technologies, etc. The presentation provides an overview of current theories on LIPSS and the quest to achieve ever smaller surface nanostructures. The historical development of the fundamental ideas behind LIPSS is presented, together with experimental approaches that make it possible to distinguish between the various LIPSS formation scenarios. Time-resolved experimental methods are required to investigate the dynamics of their formation. The presentation focuses on ultrafast time-resolved optical (pump-probe) techniques that can be used for localized point measurements or microscopic imaging, utilizing the reflection, diffraction, or coherent scattering of the probe radiation at the emerging LIPSS, while simultaneously capturing information about rapid melting, ablation, and solidification phenomena. However, given the sub-micrometric spatial periods of LIPSS, their analysis using optical radiation employed in far-field techniques remained a challenge. Therefore, short wavelengths of the probe beam in the UV range or even below are required to overcome the diffraction limit imposed in the optical spectral range. Fourth-generation light sources, namely short-wavelength (XUV or X-ray) short-pulse free-electron lasers (FELs), offer new and fascinating possibilities for resolving laser-induced structure formation on surfaces in the sub-micrometer to nanometer range and in time domains from picoseconds to several nanoseconds with a resolution in the sub-picosecond regime. On laser-irradiated semiconductor surfaces, this unique spatio-temporal resolution enables the detection of early signs of coherent/plasmonic electromagnetic scattering effects, followed by the excitation of hydrodynamic capillary waves – providing new insights into the above-mentioned debate. Recent experiments at the European XFEL used fs-time-resolved small-angle X-ray scattering (fs-SAXS) and even fs-time-resolved grazing incidence small-angle X-ray scattering (fs-GISAXS), combined with grazing-incidence diffraction (fs-GID), to reveal the dynamics of the formation of nanometric LIPSS on metals. T2 - CINSaT Herbstkolloquium 2025 CY - Kassel, Germany DA - 05.11.2025 KW - Laser-induced periodic surface structures (LIPSS) KW - Ultrashort laser pulses KW - Pump-probe measurements KW - Free-electron laser KW - Small angle X-ray scattering (SAXS) PY - 2025 AN - OPUS4-64633 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - BOOK A1 - Stoian, R. A1 - Bonse, Jörn T1 - Ultrafast Laser Nanostructuring — The Pursuit of Extreme Scales N2 - 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 KW - Laser nanostructuring KW - Surface engineering KW - Nonlinear lithography KW - Self-organization KW - Laser-induced periodic surface structures, LIPSS PY - 2023 SN - 978-3-031-14752-4 SN - 978-3-031-14751-7 DO - https://doi.org/10.1007/978-3-031-14752-4 SN - 0342-4111 VL - 239 SP - 1 EP - 1245 PB - Springer Nature Switzerland AG CY - Cham ET - 1 AN - OPUS4-57294 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kunz, C. A1 - Bonse, Jörn A1 - Spaltmann, Dirk A1 - Neumann, C. A1 - Turchanin, A. A1 - Bartolomé, J. F. A1 - Müller, F. A. A1 - Gräf, S. T1 - Tribological performance of metal-reinforced ceramic composites selectively structured with femtosecond laser-induced periodic surface structures N2 - The impact of femtosecond (fs) laser-induced periodic surface structures (LIPSS) on tribological properties was investigated for metal-reinforced ceramic composites (Al2O3-ZrO2-Nb). For this purpose, the metallic niobium (Nb) phase was selectively structured with LIPSS in an air environment with different values of the fs-laser peak fluence by near-infrared fs-laser radiation (λ = 1025 nm, τ = 300 fs, frep = 1 kHz), taking advantage of the different light absorption behavior of ceramic and metal. The tribological performance was evaluated by reciprocating sliding tests in a ball-on-disc configuration using Ringer's solution as lubricant. The surfaces were characterized before and after laser irradiation by optical microscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy and by measuring the contact angle with Ringer's solution. The LIPSS formation resulted in an increased wetting of the surface with the lubricant. Moreover, the selectively structured composite surfaces revealed a coefficient of friction significantly reduced by a factor of ~3 when compared to the non-irradiated surface. Furthermore, the formation of a laser-induced oxidation layer was detected with NbO as the most prominent oxidation state. Selectively structured composites with outstanding mechanical properties and enhanced tribological performance are of particular interest for biomedical applications. KW - Laser-induced periodic surface structures (LIPSS) KW - Femtosecond laser ablation KW - Ceramic matrix composites KW - Tribology PY - 2020 DO - https://doi.org/10.1016/j.apsusc.2019.143917 SN - 0169-4332 SN - 1873-5584 VL - 499 IS - 1 SP - 143917 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-49255 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -