Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (143)
- Vortrag (51)
- Beitrag zu einem Tagungsband (30)
- Beitrag zu einem Sammelband (28)
- Posterpräsentation (13)
- Buchkapitel (10)
Schlagworte
- Femtosecond laser (28)
- Laser-induced periodic surface structures (LIPSS) (26)
- Femtosecond laser ablation (24)
- Laser ablation (23)
- Laser processing (14)
- Radiation protection (12)
- Silicon (11)
- Laser cleaning (10)
- Ablation (9)
- Materialbearbeitung (9)
- Surface functionalization (9)
- Laser-induced X-ray emission (8)
- Nanosecond laser (8)
- Nanostructures (8)
- Ultrashort laser pulses (7)
- Laser (6)
- Röntgenstrahlung (6)
- Titanium (6)
- Ultrakurze Laserpulse (6)
- Femtosecond pulse laser (5)
- Femtosekundenlaser (5)
- High-speed optical techniques (5)
- Laser beam effects (5)
- Laser safety (5)
- Laser-induced periodic surface structures (5)
- Paper (5)
- Steel (5)
- Strahlenschutz (5)
- CIGSe (4)
- Chalcopyrite (4)
- DDT (4)
- Double-pulse experiments (4)
- Femtosecond laser processing (4)
- Friction (4)
- Laser-induced periodic surface structures, LIPSS (4)
- Laserreinigung (4)
- Micro solar cell (4)
- Microstructures (4)
- Polymer (4)
- Semiconductors (4)
- Tribology (4)
- Ultrafast optical techniques (4)
- Ultrakurzpulslaser (4)
- Ultrashort laser material interaction (4)
- X-ray emission (4)
- Abschirmung (3)
- Aluminium (3)
- Applications (3)
- Biofilms (3)
- Bone implant (3)
- Cleaning (3)
- Copper-indium-gallium-diselenide (3)
- Damage (3)
- Damage threshold (3)
- Dielectrics (3)
- Femtosecond (3)
- Femtosecond laser patterning (3)
- Fused silica (3)
- Incubation (3)
- Laser-induced damage threshold (3)
- Laser-induced forward transfer (3)
- Laser-induced forward transfer (LIFT) (3)
- Laser-induzierte Röntgenstrahlung (3)
- Laserschutz (3)
- Light concentration (3)
- Mach-Zehnder interferometer (3)
- Micromachining (3)
- Microphone (3)
- Oxidation (3)
- Photovoltaics (3)
- Secondary hazard (3)
- Silicon compounds (3)
- Silk (3)
- Surface morphology (3)
- Surface structure (3)
- Threshold (3)
- Titanium alloy (3)
- Titanium nitride (3)
- Ultrakurze Laserimpulse (3)
- Ultrashort pulse laser processing (3)
- Ultrashort pulsed laser (3)
- Wear (3)
- Acoustic measurement (2)
- Aluminium oxide (2)
- Auge (2)
- Auger electron spectroscopy (2)
- Bioceramic coating (2)
- Calcium phosphate (2)
- Cell adhesion (2)
- Decontamination (2)
- Doping (2)
- Elemental semiconductors (2)
- Femtosecond-Pulse Laser (2)
- Fluid transport (2)
- Glass (2)
- Glasses (2)
- Image enhancement (2)
- Image restoration (2)
- Indium phosphide (2)
- Laser damage (2)
- Laser impact on surfaces (2)
- Laser micromachining (2)
- Laser-beam impact phenomena (79.20.Ds) (2)
- Laser-induced x-ray emission (2)
- Lasersicherheit (2)
- Material processing (2)
- Medizinische Anwendung (2)
- Micro solar cells (2)
- Micro-concentrator solar cell (2)
- Multimode fiber (2)
- Multispectral imaging (2)
- Nanosekundenlaser (2)
- Niobium (2)
- Optical fiber (2)
- Optical multimode fiber (2)
- Optical properties (2)
- Pacemaker (2)
- Physical radiation damage (2)
- Physical radiation damage (61.80.-x) (2)
- Polaritons (2)
- Pulslaser (2)
- Radiation treatment (2)
- Röntgenemission (2)
- Scanning electron microscopy (2)
- Schutzbrille (2)
- Second harmonic generation (SHG) (2)
- Selective emitter (2)
- Silica (2)
- Silica glass (2)
- Silicon oxide (2)
- Solar cell (2)
- Subpicosecond laser ablation (2)
- Surface plasmon polaritons (2)
- Surface plasmons (2)
- Surface texture (2)
- Surface wetting (2)
- Textiles (2)
- Ultra-short pulse laser processing (2)
- Ultrafast phenomena (2)
- Wooden artworks (2)
- X-ray photoelectron spectroscopy (2)
- Zahn (2)
- (LIPSS) (1)
- Ab initio calculations (1)
- Absorber optimization (1)
- Acoustical measurement (1)
- Ageing (1)
- Aluminium alloys (1)
- Amorphization (1)
- Amorphous (1)
- Ancient manuscripts (1)
- Anodic oxidation (1)
- Anodization (1)
- Antibacterial surfaces (1)
- Application (1)
- Arbeitsschutz (1)
- Artificial soiling (1)
- Atomic force microscopy (1)
- Bacterial adhesion (1)
- Barium aluminium borosilicate glass (1)
- Bariumalumoborosilicate glass (1)
- Bariumalumoborosilicate glass surfaces (1)
- Bending strength (1)
- Bioaktives Material (1)
- Bioceramics (1)
- Biochemical reaction mechanisms and kinetics (1)
- Biofilm (1)
- Bioinspiration (1)
- Biologische Anwendungen (1)
- Biomedizin (1)
- Biomimetic surfaces (1)
- Biomometics (1)
- Bionic materials (1)
- Biosensor (1)
- Bone (1)
- Bor (1)
- Bug (1)
- CHOCLAB (1)
- CIGSe micro solar cells (1)
- Calcium compounds (1)
- Calcium phosphate coating (1)
- Carbon (81.05.Uw) (1)
- Carrier excitation (1)
- Central Asia (1)
- Cleaning threshold (1)
- Coatings (1)
- Cold atmospheric pressure plasma (1)
- Colorimetry (1)
- Conduction bands (1)
- Conservation (1)
- Copper indium gallium diselenide (CIGSe) (1)
- Copper-indium-gallium-diselenide (CIGSe) (1)
- Crystallization (1)
- Cu(In,Ga)Se2 (1)
- CuInSe2 (1)
- Cultural heritage (1)
- Defect model (1)
- Degree of polymerization (1)
- Dentistry (1)
- Diamond-like carbon (1)
- Diffusion (1)
- Doping thin films (1)
- Double-pulse (1)
- Dry Etching (1)
- Dünnfilm, diamantartig (1)
- Dünnfilmtechnologie (1)
- Dünnschicht, halbleitend (1)
- Dünnschicht, metallisch (1)
- EN 12254 (1)
- EN 207 (1)
- EN 208 (1)
- Editorial (1)
- Electrochemistry (1)
- Electromagnetic scattering (1)
- Ellipsometrie (1)
- Etch Process (1)
- European Materials Research Society (E-MRS) (1)
- European standard (1)
- Eye protection (1)
- FS-laser ablation (1)
- Farbmessung (1)
- Fatigue (1)
- Fatigue testing (1)
- Femtosecond pulses (1)
- Femtosekunden (1)
- Femtosekundenpulslaser (1)
- Fermi-Level Pinning (1)
- Fiber waveguides (1)
- Fiber waveguides (42.81.Qb) (1)
- Fictive temperature (1)
- Filter (1)
- Filterpapier (1)
- Fourier transforms (1)
- Fs-laser patterning (1)
- Glasfilter (1)
- Glass transitions (1)
- Glasses (81.05.Kf) (1)
- Glucose (1)
- Gold films (1)
- Hadernpapier (1)
- Hard X-ray photoelectron spectroscopy (HAXPES) (1)
- Heat affected zone (1)
- Hierarchical micro-nanostructures (1)
- Holz (1)
- Holzhaltiges Papier (1)
- Hydrocarbons (1)
- ISO 11254-2 (1)
- Implantat (1)
- Indium (1)
- Indium islands (1)
- Indium preferential nucleation (1)
- Industrial applications (1)
- Interfacial Electronic States (1)
- Interferometer (1)
- Justierbrille (1)
- Knochenersatz (1)
- Kohlenstoffschichten (1)
- Kunststoffschicht (1)
- Kurzpulslaser (1)
- LIDT (1)
- LIFT (1)
- Laser Machining (1)
- Laser Processing (1)
- Laser beam machining (1)
- Laser induced damage (1)
- Laser irradiation surface effects (1)
- Laser materials (1)
- Laser materials processing (1)
- Laser pulses (1)
- Laser spallation (1)
- Laser treatment (1)
- Laser-Ablation (1)
- Laser-Material-Bearbeitung (1)
- Laser-Materialbearbeitung (1)
- Laser-beam impact phenomena (1)
- Laser-induced damage (1)
- Laser-induced fixation (1)
- Laser-induced nanostructures (1)
- Laser-induced oxide layer (1)
- Laser-induced periodic surface strctures (LIPSS) (1)
- Laser-induced periodic surface strcutures (LIPSS) (1)
- Laser-material interactions (1)
- Laser-modified surface (1)
- Laserinduzierte Zerstörschwelle (1)
- Lasermaterialbearbeitung (1)
- Lasermikrobearbeitung (1)
- Lasersintern (1)
- Lasertechnik (1)
- Lichtwellenleiter (1)
- Lizard (1)
- MOS Diode (1)
- Materials processing (1)
- Mechanical stress (1)
- Melting (1)
- Membrane perforation (1)
- Metallprothese (1)
- Metals (1)
- Michelson interferometer (1)
- Micro-concentrator (1)
- Microbial adhesion tests (1)
- Microbial adhesions (1)
- Microconcentrator solar cell (1)
- Microscopy (1)
- Microsecond laser (1)
- Microstructuring (1)
- Mikrobearbeitung (1)
- Mikroskopie (1)
- Molybdenum substrate (1)
- Multi-Photon Absorption (1)
- Multicrystalline silicon (1)
- Multiple-pulse damage (1)
- Nanosecond Pulses (1)
- Nanosecond laser cleaning (1)
- Nanostrcutures (1)
- Nd:YAG laser (1)
- Nd:YAG-Laser (1)
- Nonlinear Electroreflectance (1)
- Oberflächenstrukturierung (1)
- Ophthalmology (1)
- Optical breakdown (1)
- Optical coatings (1)
- Optical constants (78.20.Ci) (1)
- Optical fibers (1)
- Optical microscopy (1)
- Optical proper (1)
- Optics at surfaces (1)
- Optische Konstanten (1)
- Optische Multimodefaser (1)
- Orthopaedics (1)
- Oxide (1)
- Oxide growth (1)
- Papery (1)
- Parchment (1)
- Personal protective equipment (1)
- Photochemical reactions of biomolecules (1)
- Photoelektron spectroscopy (1)
- Photovoltaik (1)
- Physical vapor deposition (1)
- Picture Post Card (1)
- Pigments (1)
- Polarisation (1)
- Poly(methylmetacrylate) (1)
- Polycarbonate (1)
- Polyethylene (1)
- Polymer ablation (1)
- Polymerfilter (1)
- Polymers (1)
- Polymers-radiation effects (1)
- Polymethylmethacrylate (1)
- Probekörper (1)
- Prosthetics (1)
- Protection housing (1)
- Pulse Laser (1)
- Pulse duration (1)
- Radiation treatment (81.40.Wx) (1)
- Refractive index (1)
- Reproducibility (1)
- Ripples (1)
- Rods (structures) (1)
- Round-robin experiment (1)
- S on 1-LIDT (1)
- SHG (1)
- SIMS (1)
- Scanning Auger electron microscopy (1)
- Second-Harmonic Generation (1)
- Sekundärstrahlung (1)
- Semiconductor (1)
- Semiconductor electrode (1)
- Silicon nitride (1)
- Silicon solar cell (1)
- Silk Road (1)
- Simulation (1)
- Single- and multi-shot ablation (1)
- Solid electrolyte interface (1)
- Solid-state plasma (1)
- Spectroscopic imaging ellipsometry (1)
- Spectroscopy (1)
- Spot size (1)
- Spring Meeting 2016 (1)
- Structuring (1)
- Sub-Picosecond-Pulse Laser (1)
- Subpicosecond-Pulse Laser (1)
- Superconductivity (1)
- Surface and interface chemistry of polymers (1)
- Surface plasmon polariton (1)
- Surface processing (1)
- Surface superconductivity (1)
- Surface treatment (1)
- Technische Materialien (1)
- Textile (1)
- Thin films (1)
- Threshold fluence (1)
- Threshold of silicon (1)
- Ti-6Al-4V alloy (1)
- Ti6Al4V alloys (1)
- Ti:sapphire laser (1)
- Time-of-flight secondary ion mass spectrometry (ToF-SIMS) (1)
- Time-resolved measurements (1)
- Time-resolved reflectivity measurements (1)
- Titanium alloys (1)
- Titanium nitride films (1)
- Treshold (1)
- Tungsten (1)
- Ultrashort lasers (1)
- Ultrashort pulse laser (1)
- Vanadium alloys (1)
- Verrußung (1)
- Viscometry (1)
- Wall paintings (1)
- Wandmalerei (1)
- Water (1)
- Wetting (1)
- Wood (1)
- X-ray (1)
- X-ray diffraction (1)
- X-ray emission hazards (1)
- X-ray energies (1)
- X-ray spectrum (1)
- fused silica (1)
- laser damage (1)
- lossy materials (1)
- nanosecond laser (1)
- optical fiber (1)
- plasmon lifetime (1)
- surface plasmon polaritons (1)
Organisationseinheit der BAM
- 6 Materialchemie (56)
- 6.2 Material- und Oberflächentechnologien (56)
- 9 Komponentensicherheit (4)
- 9.5 Tribologie und Verschleißschutz (4)
- 6.7 Materialsynthese und Design (3)
- 4 Material und Umwelt (2)
- 4.1 Biologische Materialschädigung und Referenzorganismen (2)
- 6.1 Oberflächen- und Dünnschichtanalyse (2)
- 5 Werkstofftechnik (1)
- 5.1 Mikrostruktur Design und Degradation (1)
Paper des Monats
- ja (3)
The use of ultrashort laser pulses for material processing in air has many advantages. Due to the progressive development in the laser sector, average powers in the kW range with pulse repetition rates exceeding the MHz-level are available. The machining with high-intensity laser pulses can be accompanied by the generation of a near-surface electron plasma due to absorption and ionization of the material, a subsequent plasma heating by the laser pulse, and finally an interaction of “hot” plasma electrons with the workpiece leading to continuous and characteristic X-ray radiation. The amount of this unwanted X-ray radiation is determined by the laser parameters (pulse duration, intensity, wavelength, polarization), the workpiece (atomic number, surface preparation), and the laser process management (scanning or stationary regime, laser turning). The use of laser intensities above 10^13 W/cm^2 in combination with laser pulse repetition rates in the few 100 kHz-range can lead to X-ray dose rates exceeding the permitted X-ray limits for members of the public. Especially the materials tungsten and steel show significant X-ray emission. Recently, the current state of the art in the field of undesired generation of X-ray radiation during ultrashort pulse laser processing in air was reviewed. In this presentation, important aspects of the measured X-ray doses, X-ray spectra, and practical issues of radiation protection are discussed.
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 wavelengths, pulse durations and repetition rate laser sources, customized micro- and nanometric spatial resolutions, and 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.
Ultrashort pulse laser microstructuring (pulse duration 130 fs, wavelength 800 nm, repetition rate 2 Hz) of titanium nitride (TiN) films on silicon substrates was performed in air using the direct focusing technique. The lateral and vertical precision of laser ablation was evaluated. The TiN ablation threshold changed with the number of pulses applied to the surface due to an incubation effect. An ablation depth per pulse below the penetration depth of light was observed. Columnar structures were formed in the silicon substrate after drilling through the TiN layer.
The chemical characteristics of two different types of laser-induced periodic surface structures (LIPSS), so-called high and low spatial frequency LIPSS (HSFL and LSFL), formed upon irradiation of titanium surfaces by multiple femtosecond laser pulses in air (30 fs, 790 nm, 1 kHz), are analyzed by various optical and electron beam based surface analytical techniques, including micro-Raman spectroscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, and Auger electron spectroscopy. The latter method was employed in a high-resolution mode being capable of spatially resolving even the smallest HSFL structures featuring spatial periods below 100 nm. In combination with an ion sputtering technique, depths-resolved chemical information of superficial oxidation processes was obtained, revealing characteristic differences between the two different types of LIPSS. Our results indicate that a few tens of nanometer shallow HSFL are formed on top of a ∼150 nm thick graded superficial oxide layer without sharp interfaces, consisting of amorphous TiO2 and partially crystallized Ti2O3. The larger LSFL structures with periods close to the irradiation wavelength originate from the laser-interaction with metallic titanium. They are covered by a ∼200 nm thick amorphous oxide layer, which consists mainly of TiO2 (at the surface) and other titanium oxide species of lower oxidation states underneath.
Ultrashort pulse laser materials processing can be accompanied by the production of X-rays. Small doses per laser pulse can accumulate to significant dose rates at high laser pulse repetition rates which may exceed the permitted X-ray limits for human exposure. Consequently, a proper radiation shielding must be considered in laser machining. A brief overview of the current state of the art in the field of undesired generation of X-ray radiation during ultrashort pulse laser material processing in air is presented.
The industrial use of ultrashort laser pulses has made considerable progress in recent years. The reasons for this lie in the availability of high average powers at pulse repetition rates in the several 100 kHz range. The advantages of using ultrashort laser pulses in terms of processing precision can thus be fully exploited. However, high laser intensities on the workpiece can also lead to the generation of unwanted X-rays. Even if the emitted X-ray dose per pulse is low, the accumulated X-ray dose can become significant for high-repetition-rate laser systems so that X-ray exposure safety limits must be considered. The X-ray emission during ultrashort pulse laser processing was investigated for a pulse duration of 925 fs at 1030 nm wavelength and 400 kHz repetition rate. Industrially relevant materials such as steel,aluminum and glass were treated. Tungsten served as reference. X-ray spectra were recorded, and X-ray dose measurements were performed for laser treatment in air. For laser intensities > 2 × 10^13 W/cm2, X-ray doses exceeding the regulatory exposure limits for members of the public were found. Suitable X-ray protection strategies are proposed.
The current state in the field of laser-induced periodic surface structures (LIPSS, ripples) is reviewed. Their formation mechanisms are analyzed in ultrafast experiments (time-resolved diffraction and polarization controlled double-pulse experiments) and technological applications are demonstrated.
The formation of laser-induced periodic surface structures (LIPSS) in different materials (metals, semiconductors, and dielectrics) upon irradiation with linearly polarized fs-laser pulses (τ~30–150 fs, λ~800 nm) in air environment is studied experimentally and theoretically. In metals, predominantly low-spatial-frequency-LIPSS with periods close to the laser wavelength λ are observed perpendicular to the polarization. Under specific irradiation conditions, high-spatial-frequency-LIPSS with sub-100-nm spatial periods (~λ/10) can be generated. For semiconductors, the impact of transient changes of the optical properties to the LIPSS periods is analyzed theoretically and experimentally. In dielectrics, the importance of transient excitation stages in the LIPSS formation is demonstrated experimentally using (multiple) double-fs-laser-pulse irradiation sequences. A characteristic decrease of the LIPSS periods is observed for double-pulse delays of less than 2 ps.
Laser texturing is an emerging technology for generating surface functionalities on basis of optical, mechanical, or chemical properties. Taking benefit of laser sources with ultrashort (fs) pulse durations features outstanding precision of machining and negligible rims or burrs surrounding the laser-irradiation zone. Consequently, additional mechanical or chemical post-processing steps are usually not required for fs-laser surface texturing (fs-LST). This work aimed to provide a bridge between research in the field of tribology and laser materials processing. The paper reviews the current state-of-the-art in fs-LST, with a focus on the tribological performance (friction and wear) of specific self-organized surface structures (so-called ripples, grooves, and spikes) on steel and titanium alloys. On the titanium alloy, specific sickle-shaped hybrid micro-nanostructures were also observed and tribologically tested. Care is taken to identify accompanying effects affecting the materials hardness, superficial oxidation, nano- and microscale topographies, and the role of additives contained in lubricants, such as commercial engine oil.
The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica with multiple irradiation sequences consisting of laser pulse pairs (50 fs single-pulse duration) of two different wavelengths (400 and 800 nm) is studied experimentally. Parallel polarized double-pulse sequences with a variable delay Δt between -10 and +10 ps and between the individual fs-laser pulses were used to investigate the LIPSS periods versus Δt. These two-color experiments reveal the importance of the ultrafast energy deposition to the silica surface by the first laser pulse for LIPSS formation. The second laser pulse subsequently reinforces the previously seeded spatial LIPSS frequencies.
Two-color double-fs-pulse experiments were performed on silicon wafers to study the temporally distributed energy deposition in the formation of laser-induced periodic surface structures (LIPSS). A Mach-Zehnder interferometer generated parallel or cross-polarized double-pulse sequences at 400 and 800 nm wavelength, with inter-pulse delays up to a few picoseconds between the sub-ablation 50-fs-pulses. Multiple two-color double-pulse sequences were collinearly focused by a spherical mirror to the sample. The resulting LIPSS characteristics (periods, areas) were analyzed by scanning electron microscopy. A wavelength-dependent plasmonic mechanism is proposed to explain the delay-dependence of the LIPSS. These two-color experiments extend previous single-color studies and prove the importance of the ultrafast energy deposition for LIPSS formation.
The formation of laser-induced periodic surface structures (LIPSS) on different materials (silicon, fused silica, quartz) with linearly polarized fs-laser irradiation is studied experimentally. In dielectrics, the importance of transient excitation stages in the LIPSS formation is demonstrated by using (multiple) cross-polarized double-fs-laser-pulse irradiation sequences. A characteristic decrease of the spatial LIPSS periods is observed for double-pulse delays of less than 2 ps along with a characteristic 90°-rotation of the LIPSS orientation.
The formation of laser-induced periodic surface structures (LIPSS, ripples) upon irradiation of silicon with multiple irradiation sequences consisting of femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied numerically using a rate equation system along with a two-temperature model accounting for one- and two-photon absorption and subsequent carrier diffusion and Auger recombination processes. The temporal delay between the individual equal-energy fs-laser pulses was varied between 0 and ~4 ps for quantification of the transient carrier densities in the conduction band of the laser-excited silicon. The results of the numerical analysis reveal the importance of carrier generation and relaxation processes in fs-LIPSS formation on silicon and quantitatively explain the two time constants of the delay-dependent decrease of the low spatial frequency LIPSS (LSFL) area observed experimentally. The role of carrier generation, diffusion and recombination is quantified individually.
The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of silicon by multiple (N = 100) linearly polarized Ti:sapphire femtosecond laser pulses (duration τ = 30 fs, center wavelength λ0 ~ 790 nm) is studied experimentally in air and water environment. The LIPSS surface morphologies are characterized by scanning electron microscopy and their spatial periods are quantified by two-dimensional Fourier analyses. It is demonstrated that the irradiation environment significantly influences the periodicity of the LIPSS. In air, so-called low-spatial frequency LIPSS (LSFL) were found with periods somewhat smaller than the laser wavelength (ΛLSFL ~ 0.7 × λ0) and an orientation perpendicular to the laser polarization. In contrast, for laser processing in water a reduced ablation threshold and LIPSS with approximately five times smaller periods ΛLIPSS ~ 0.15 × λ0 were observed in the same direction as in air. The results are discussed within the frame of recent LIPSS theories and complemented by a thin film based surface plasmon polariton model, which successfully describes the tremendously reduced LIPSS periods in water.
The dynamics of the formation of laser-induced periodic surface structures (LIPSS) on fused silica upon irradiation with linearly polarized fs-laser pulses (50 fs pulse duration) is studied by cross-polarized two-color double-fs-pulse experiments. In order to analyze the relevance of temporally distributed energy deposition in the early stage of LIPSS formation, a Mach-Zehnder interferometer was used for generating multiple double-pulse sequences at two different wavelengths (400 and 800 nm). The inter-pulse delay between the individual cross-polarized pulses of each sequence was systematically varied in the sub-ps range and the resulting LIPSS morphologies were characterized by scanning electron microscopy. It is found that the polarization of the first laser pulse arriving to the surface determines the orientation and the periodicity of the LIPSS. These two-color experiments further confirm the importance of the ultrafast energy deposition to the silica surface for LIPSS formation, particularly by the first laser pulse of each sequence. The second laser pulse subsequently reinforces the previously seeded spatial LIPSS characteristics (period, orientation).
A promising technology in photovoltaics is based on micro-concentrator solar cells, where the photovoltaic active area is realized as an array of sub-millimeter sized cells onto which the incident light is focused via microlenses. This approach allows to increase the cell efficiency and to realize much more compact modules compared to macroscopic concentrator devices. At the same time, expensive raw materials can be saved, which is of interest, for example, with respect to indium in the case of copper-indium-gallium-diselenide (CIGSe) thin film solar cells. Two methods to produce micro-sized precursors of CIGSe absorbers on molybdenum are presented using 30-fs laser pulses at 790 nm wavelength. On the one hand, a multi pulse surface structuring of the molybdenum film or the underlying glass substrate and a subsequent physical vapor deposition were used for a site-selective aggregation of indium droplets. On the other hand, a single pulse laser-induced forward transfer was utilized to selectively deposit combined copper-indium precursor pixels on the molybdenum back contact of the solar cell. Post-processing (selenization, isolation, contacting) of the laser-generated micro-sized precursors results in functional CIGSe solar cells.
We investigate the periodic structure formation upon intense femtosecond pulsed irradiation of chrome steel (100Cr6) for linearly polarised laser beams. The underlying physical mechanism of the laser-induced periodic structures is explored, their spatial frequency is calculated and theoretical results are compared with experimental observations. The proposed theoretical model comprises estimations of electron excitation, heat transfer, relaxation processes, and hydrodynamics-related mass transport. Simulations describe the sequential formation of sub-wavelength ripples and supra-wavelength grooves. In addition, the influence of the laser wavelength on the periodicity of the structures is discussed. The proposed theoretical investigation offers a systematic methodology towards laser processing of steel surfaces with important applications.
A laser-based bottom-up technique for the fabrication of Cu(In,Ga)Se2 (CIGSe) micro solar cells is presented.
We use femtosecond laser-induced forward transfer (LIFT) to transport a metallic precursor composed of copper, indium, and gallium onto a molybdenum back contact layer on a glass substrate. A CIGSe absorber forms by subsequent selenization. An array of micro absorbers with defined spacing is fabricated to solar cells and characterized under concentrated light illumination. The solar cell array exhibited a conversion efficiency of 1.4‰ at 1 sun as well as a significant efficiency enhancement of 68% rel. under 20-fold concentration. This work demonstrates the possibility of directly grown micrometer-sized solar cells based on chalcogenide absorber layers, enabling effective material usage.
Laser-induced periodic surface structures (LIPSS) are a universal phenomenon and can be generated on almost any material by irradiation with linearly polarized radiation. This chapter reviews the current state in the field of LIPSS, which are formed in a “self-ordered” way and are often accompanying materials processing applications. LIPSS can be produced in a single-stage process and enable surface nanostructuring and, in turn, adaption of optical, mechanical, and chemical surface properties. Typically, they feature a structural size ranging from several micrometers down to less than 100 nm and show a clear correlation with the polarization direction of the light used for their generation. Various types of LIPSS are classified, relevant control parameters are identified, and their material-specific formation mechanisms are analyzed for different types of inorganic solids, i.e., metals, semiconductors, and dielectrics. Finally, technological applications featuring surface functionalization in the fields of optics, fluidics, medicine, and tribology are discussed.
The exciting properties of micro- and nano-patterned surfaces found in natural species hide a virtually endless potential of technological ideas, opening new opportunities for innovation and exploitation in materials science and engineering. Due to the diversity of biomimetic surface functionalities, inspirations from natural surfaces are interesting for a broad range of applications in engineering, including phenomena of adhesion, friction, wear, lubrication, wetting phenomena, self-cleaning, antifouling, antibacterial phenomena, thermoregulation and optics. Lasers are increasingly proving to be promising tools for the precise and controlled structuring of materials at micro- and nano-scales. When ultrashort-pulsed lasers are used, the optimal interplay between laser and material parameters enables structuring down to the nanometer scale. Besides this, a unique aspect of laser processing technology is the possibility for material modifications at multiple (hierarchical) length scales, leading to the complex biomimetic micro- and nano-scale patterns, while adding a new dimension to structure optimization. This article reviews the current state of the art of laser processing methodologies, which are being used for the fabrication of bioinspired artificial surfaces to realize extraordinary wetting, optical, mechanical, and biological-active properties for numerous applications. The innovative aspect of laser functionalized biomimetic surfaces for a wide variety of current and future applications is particularly demonstrated and discussed. The article concludes with illustrating the wealth of arising possibilities and the number of new laser micro/nano fabrication approaches for obtaining complex high-resolution features, which prescribe a future where control of structures and subsequent functionalities are beyond our current imagination.
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.
A procedure to fabricate CuInSe2 (CISe) micro-absorbers and solar cells for concentrator applications is presented. The micro-absorbers are developed from indium precursor islands, which are deposited on a molybdenum coated glass substrate (back contact), followed by deposition of copper on top and subsequent selenization as well as selective etching of copper selenides. In order to compare the properties of the locally grown absorbers to those of conventional large area CISe films, we systematically examine the compositional and morphological homogeneity of the micro absorbers and carry out photoluminescence measurements. Preliminary devices for micro-concentrator solar cell applications are fabricated by optimizing the copper to indium ratio and the size of the indium precursor islands. The resulting micro solar cells provide a characteristic I–V curve under standard illumination conditions (1 sun).
Surface nanostructures provide the possibility to create and tailor surface functionalities mainly via controlling their topography along with other chemical and physical material properties. One of the most appealing technologies for surface functionalization via micro- and nanostructuring is based on laser processing. This can be done either via direct contour-shaping of the irradiated material using a tightly focused laser beam or in a self-ordered way that allows employing larger laser beam diameters along with areal scanning to create a variety of laser-induced periodic surface structures (LIPSS). For the latter approach, particularly ultrashort pulsed lasers have recently pushed the borders across long-lasting limitations regarding the minimum achievable feature sizes and additionally boosted up the production times. This chapter reviews the plethora of recently investigated applications of LIPSS—for example, via imposing diffractive or plasmonic structural colors, the management of liquids and surface wetting properties, biomedical and bioinspired functionalities, beneficial effects in tribology for reducing friction and wear, the manipulation of optical scattering and absorption in photovoltaics, or the modification of magnetic or superconducting surface properties in other energy applications. The footprint of the LIPSS-based technology is explored in detail regarding the current state of industrialization, including an analysis of the market and associated LIPSS production costs.