Article
Optics
Zbynek Hubka, Roman Antipenkov, Robert Boge, Emily Erdman, Michael Greco, Jonathan T. Green, Martin Horacek, Karel Majer, Tomas Mazanec, Petr Mazurek, Jack A. Naylon, Jakub Novak, Vaclav Sobr, Petr Strkula, Murat Torun, Boguslaw Tykalewicz, Pavel Bakule, Bedrich Rus
Summary: This research presents a 1 kHz, 515 nm laser system based on commercially available equipment, developed for pumping the OPCPA stage of the Allegra laser system, with a series of techniques employed to ensure stability and high efficiency.
Article
Materials Science, Multidisciplinary
Jiaming Wu, Yuying Zhang, LingQi Li, Yingying Ren, Qingming Lu, Lei Wang, Feng Chen
Summary: Direct femtosecond laser writing is an efficient technique for microstructuring transparent materials, inducing refractive index modifications to construct waveguide structures. Different wavelength laser pulses were used to form single-line tracks in glass, with high-resolution confocal Raman spectra obtained in the track regions to investigate the physical mechanisms of the modification.
RESULTS IN PHYSICS
(2021)
Article
Engineering, Manufacturing
Marc Hummel, Mike Kuelkens, Christoph Schoeler, Wolfgang Schulz, Arnold Gillner
Summary: The paramount challenge in laser micro welding is to design welding processes that are highly energy efficient and precise in controlling weld depth and surface roughness. Copper's high thermal conductivity and low energy absorption under infrared radiation present difficulties in the process, leading to a higher interest in visible wavelength lasers as an alternative to near infrared lasers. Investigation into in situ X-ray tomography experiments during laser beam welding of copper with 515 nm and 1030 nm laser sources revealed significant differences in the depth of the keyhole and sensitivity to variations in feed rate and laser power between the two wavelengths.
JOURNAL OF MANUFACTURING PROCESSES
(2021)
Article
Materials Science, Multidisciplinary
Wendwesen Gebremichael, Christophe Dorrer, Jie Qiao
Summary: We conducted a comparative investigation on the fabrication of type-II waveguide lasers in Nd:YAG using femtosecond laser pulses at 515 and 1030 nm. We focused on comparing track morphologies, modification thresholds, and overall efficiency of the ultrafast laser inscription process. Low propagation losses of 0.2 dB/cm were achieved at both wavelengths. The lowest reported lasing threshold of 9 mW was achieved in a Nd:YAG waveguide laser. Superior performance was obtained with the 1030-nm ULI source, with a slope efficiency over 40% and a lasing threshold half of that observed for the 515-nm source.
JOURNAL OF LASER APPLICATIONS
(2023)
Article
Materials Science, Multidisciplinary
Florian Kaufmann, Carola Forster, Marc Hummel, Alexander Olowinsky, Felix Beckmann, Julian Moosmann, Stephan Roth, Michael Schmidt
Summary: Laser welding of copper is increasingly used in electric components applications. However, the combination of energy efficiency and precise process guidance is a challenge due to copper's high electrical and thermal conductivity. High-power lasers in the near infrared wavelength range provide a solution, but novel beam sources at visible wavelengths are needed for improved efficiency. In this study, 515 nm and 1030 nm laser sources were compared to understand their influence on the vapor capillary geometry during welding.
Proceedings Paper
Engineering, Electrical & Electronic
R. E. Scott, Z. Guo, P. E. Sahoo, C. Dorrer, J. Qiao
Summary: A dynamic pulse propagation model was developed to compare the interaction of femtosecond pulses at 1030 nm and 515 nm with transparent materials, predicting that the shorter wavelength will lead to more effective welding.
2021 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO)
(2021)
Proceedings Paper
Engineering, Multidisciplinary
Marc Hummel, Christian Meier, Alexander Olowinsky, Arnold Gillner, Felix Beckmann, Julian Moosmann, Constantin Haefner
Summary: Laser welding is becoming increasingly important for manufacturing precise parts for electronic and electro mobility components. The challenge lies in welding highly reflective materials like copper with high thermal conductivity. This study used synchrotron radiation to observe laser welding processes on copper alloys using laser beam sources with wavelengths of 1030 nm and 515 nm. The results showed that the two welding processes had different vapor capillary geometry and sensitivity to feed rate changes. The 1030 nm welding process had better overall weld seam quality and was more sensitive to feed rate changes, while comparatively higher feed rates led to better welding results with 515 nm.
HIGH-POWER LASER MATERIALS PROCESSING: APPLICATIONS, DIAGNOSTICS, AND SYSTEMS XII
(2023)
Article
Engineering, Manufacturing
Jannik Lind, Niklas Weckenmann, Christian Hagenlocher, Rudolf Weber, Thomas Graf
Summary: The study shows that increasing the repetition rate of laser pulses can reduce the piercing duration, but when the frequency exceeds a specific limit, the growth of piercing depth stagnates and the laser cannot penetrate the sheet completely.
JOURNAL OF MANUFACTURING PROCESSES
(2021)
Article
Optics
Florian Bienert, Thomas Graf, Marwan Abdou Ahmed
Summary: This paper presents a theoretical investigation on the application of laser interference lithography for the exposure of linear gratings. The focus is on the geometry of the interference lines on the substrate, specifically their period and orientation, depending on the illumination geometry determined by the setup.
Article
Materials Science, Multidisciplinary
David Brinkmeier, Daniel Holder, Andre Loescher, Christoph Roecker, Daniel J. Foerster, Volkher Onuseit, Rudolf Weber, Marwan Abdou Ahmed, Thomas Graf
Summary: Commercial ultrafast lasers with kW power levels show potential for high-volume manufacturing, but limitations such as particle shielding, atmosphere breakdown, and heat accumulation need to be addressed. Experimental validation of a thermal model for AISI 304 steel drilling highlights the importance of a critical heat accumulation threshold. A processing map summarizes these limits and provides guidance for parameter selection and laser suitability, stressing the importance of process parallelization.
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING
(2022)
Article
Materials Science, Multidisciplinary
Gerd Reichardt, Manuel Henn, Paul Reichle, Georg Umlauf, Kim Riedmueller, Rudolf Weber, Jakob Barz, Mathias Liewald, Thomas Graf, Guenter E. M. Tovar
Summary: In the deep drawing process, lubricants are essential to prevent wear and surface damage, but traditional options pose environmental and health risks, leading to research on a new system using liquid carbon dioxide and nitrogen gas introduced through micro-holes. Further investigations are focused on the lubrication medium's impact on tool wear.
Article
Optics
Christoph Roecker, Pascal Weinert, Philippe Villeval, Dominique Lupinski, Martin Delaigue, Clemens Hoenninger, Rudolf Weber, Thomas Graf, Marwan Abdou Ahmed
Summary: This study reports on the analysis of nonlinear absorption in lithium triborate (LBO) for second and third harmonic generation. The absorption coefficients were estimated using thermographic imaging and numerical modeling, and high power harmonic generation results were obtained.
Article
Nanoscience & Nanotechnology
Marwan Abdou Ahmed, Frieder Beirow, Andre Loescher, Tom Dietrich, Danish Bashir, Denys Didychenko, Anton Savchenko, Christof Pruss, Marina Fetisova, Fangfang Li, Petri Karvinen, Markku Kuittinen, Thomas Graf
Summary: This study demonstrates the intracavity generation of beams with radial polarization using circular grating waveguide output couplers and the conversion of femtosecond laser pulses from linear to azimuthal polarization using a nanograting-based polarization converter. The optimization of the duty cycle and geometrical profile of the gratings can enhance the stability and performance of the polarization function.
Article
Optics
Uwe Brauch, Christoph Roecker, Thomas Graf, Marwan Abdou Ahmed
Summary: The development of high-power diode lasers has enabled the realization of solid-state lasers based on trivalent ytterbium, resulting in improved efficiency and beam quality of continuous wave lasers, as well as the achievement of high average power ultrafast lasers. These lasers offer advantages in terms of thermo-optical properties and the ability to obtain specific laser properties.
APPLIED PHYSICS B-LASERS AND OPTICS
(2022)
Article
Optics
Pascal J. Weinert, Marius Grossmann, Uwe Brauch, Michael Jetter, Peter Michler, Thomas Graf, Marwan Abdou Ahmed
Summary: A high-power output was achieved in a VECSEL using an AlGaAs material and diode pumping. The study highlights the importance of balancing low heat generation and strong absorption by choosing the appropriate barrier material, and emphasizes the significance of effective heat removal for power scaling of VECSELs.
Article
Chemistry, Physical
Julian Holland, Rudolf Weber, Marc Sailer, Thomas Graf
Summary: This study investigates and simulates soft X-ray emissions during the processing of industrial materials with ultrafast lasers. Experimental data verifies a model that extends an existing analytical model to consider the influence of laser pulse duration on the fraction of hot electrons in the generated plasma.
Proceedings Paper
Engineering, Manufacturing
Michael Sawannia, Peter Berger, Rudolf Weber, Thomas Graf
Summary: In this study, the melt flow velocity and local surface angles of the cutting front during laser fusion cutting of 10 mm AISI 304 were determined using a polarization goniometer. Different structures moving along the cutting front were identified, with small structures having an approximate velocity of 9.1 m/s and big structures around 2.5 m/s. This information was compared with data obtained from a usual high-speed video.
18TH NORDIC LASER MATERIALS PROCESSING CONFERENCE (18TH NOLAMP)
(2021)
Proceedings Paper
Engineering, Manufacturing
Jonas Wagner, Peter Berger, Philipp He, Florian Fetzer, Rudolf Weber, Thomas Graf
Summary: A reduced two-dimensional finite-volume model was proposed in this paper for fast calculation of melt flow during laser beam welding of aluminium. The model revealed the different effects of welding speed and viscosity on the resulting weld-pool geometry, with viscosity playing a more significant role at lower welding speeds and friction at keyhole walls being more pronounced at higher welding speeds. The weld-pool geometry was found to be mainly dependent on the welding speed.
18TH NORDIC LASER MATERIALS PROCESSING CONFERENCE (18TH NOLAMP)
(2021)
Proceedings Paper
Engineering, Manufacturing
Daniel Holder, Matthias Buser, Artur Leis, Rudolf Weber, Thomas Graf
Summary: The study explored post-processing of LPBF-generated Ti6Al4V parts using ultrashort pulse laser ablation, which successfully removed support structures, reduced surface roughness by 81%, and fabricated complex geometries with high shape accuracy. Additionally, laser surface structuring of the parts changed the wetting behavior from hydrophilic to hydrophobic, increasing the contact angle from 73 degrees to 130 degrees.
18TH NORDIC LASER MATERIALS PROCESSING CONFERENCE (18TH NOLAMP)
(2021)
Proceedings Paper
Engineering, Manufacturing
Jannik Lind, Christian Hagenlocher, David Blazquez-Sanchez, Marc Hummel, A. Olowinsky, Rudolf Weber, Thomas Graf
Summary: In laser fusion cutting of aluminum sheets, the occurrence of interrupted striations on the cut edge leads to higher surface roughness compared to regular striations. This is due to fluctuations in the local angle of incidence and the increase in average absorbed irradiance, resulting in a thicker melt film at the cutting front which is responsible for the formation of interrupted striations.
18TH NORDIC LASER MATERIALS PROCESSING CONFERENCE (18TH NOLAMP)
(2021)
Article
Optics
Frieder Beirow, Johannes Wahl, Rico Hohmuth, Andreas Richter, Christof Pruss, Cherry May Mateo, Thomas Graf, Marwan Abdou Ahmed
Summary: This paper investigates two different approaches based on grating waveguide structures to generate radially polarized ultra-short pulses in thin-disk laser resonators. By using a highly reflective GWS instead of a partly reflective GWS, significant improvement in optical efficiency can be achieved.
Article
Engineering, Manufacturing
Dina Becker, Steffen Boley, Rocco Eisseler, Thomas Stehle, Hans-Christian Moehring, Volkher Onuseit, Max Hossfeld, Thomas Graf
Summary: This paper discusses the interdependence between additive and subtractive manufacturing processes, using closed loop control to achieve optimal part accuracy and minimal wall thickness during additive manufacturing. Final part shapes are achieved through subsequent machining processes with minimized material removal, dependent on the initial state determined by the additive process. Understanding the relationship between generative parameters and component properties, as well as the interdependency between additive and subtractive processes, is crucial for tuning the former to the latter.
PRODUCTION ENGINEERING-RESEARCH AND DEVELOPMENT
(2021)
