Bavarian Laser Center GmbH

Erlangen, Germany

Bavarian Laser Center GmbH

Erlangen, Germany
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Miyamoto I.,Osaka University | Cvecek K.,Bavarian Laser Center GmbH | Schmidt M.,Bavarian Laser Center GmbH | Schmidt M.,Friedrich - Alexander - University, Erlangen - Nuremberg
Optics Express | Year: 2011

Thermal conduction model is presented, by which nonlinear absorptivity of ultrashort laser pulses in internal modification of bulk glass is simulated. The simulated nonlinear absorptivity agrees with experimental values with maximum uncertainty of ±3% in a wide range of laser parameters at 10ps pulse duration in borosilicate glass. The nonlinear absorptivity increases with increasing energy and repetition rate of the laser pulse, reaching as high as 90%. The increase in the average absorbed laser power is accompanied by the extension of the laser-absorption region toward the laser source. Transient thermal conduction model for three-dimensional heat source shows that laser energy is absorbed by avalanche ionization seeded by thermally excited free-electrons at locations apart from the focus at pulse repetition rates higher than 100kHz. © 2011 Optical Society of America.


Miyamoto I.,Osaka University | Cvecek K.,Bavarian Laser Center GmbH | Okamoto Y.,Okayama University | Schmidt M.,Bavarian Laser Center GmbH | And 2 more authors.
Optics Express | Year: 2011

The nonlinear absorptivity of FOTURAN glass to ultrashort laser pulses is evaluated by experimental measurement and thermal conduction model at different parameters including energy and repetition rate of the laser pulse, translation speed and thermal properties of the sample. The mechanical strength of an embedded laser-melted sample and an overlapped weld sample is determined by a three-point-bending test and a shear test, respectively. The results are related to the average absorbed laser power Wab. We found the mechanical strength of an overlapped weld joint to be as high as that of the base material for low W ab, if the sample pair is pre-bonded to provide optical contact. © 2011 Optical Society of America.


Miyamoto I.,Osaka University | Cvecek K.,Bavarian Laser Center GmbH | Schmidt M.,Bavarian Laser Center GmbH | Schmidt M.,Friedrich - Alexander - University, Erlangen - Nuremberg
Optics Express | Year: 2013

The spatial distribution of the laser energy absorbed by nonlinear absorption process in bulk glass w(z) is determined and thermal cycles due to the successive ultrashort laser pulse (USLP) is simulated using w(z) based on the transient thermal conduction model. The thermal stress produced in internal melting of bulk glass by USLP is qualitatively analyzed based on a simple thermal stress model, and crack-free conditions are studied in glass having large coefficient of thermal expansion. In heating process, cracks are prevented when the laser pulse impinges into glass with temperatures higher than the softening temperature of glass. In cooling process, shrinkage stress is suppressed to prevent cracks, because the embedded molten pool produced by nonlinear absorption process behaves like an elastic body under the compressive stress field unlike the case of CW-laser welding where the molten pool having a free surface produced by linear absorption process is plastically deformed under the compressive stress field. © 2013 Optical Society of America.


Miyamoto I.,Osaka University | Cvecek K.,Bavarian Laser Center GmbH | Schmidt M.,Friedrich - Alexander - University, Erlangen - Nuremberg
Physics Procedia | Year: 2011

Thermal conduction model is presented, by which nonlinear absorptivity of ultrashort laser pulses in internal modification of bulk glass is simulated. The simulated nonlinear absorptivity agrees with experimental values with maximum uncertainty of ±3% in a wide range of laser parameters at 10ps pulse duration in borosilicate glass. The nonlinear absorptivity increases with increasing energy and repetition rate of the laser pulse, reaching as high as 90%. The increase in the average absorbed laser power is accompanied by the extension of the laser-absorption region toward the laser source, suggesting the seed electrons for avalanche ionization are provided mainly by thermal excitation at locations apart from the focus. © 2011 Published by Elsevier Ltd.


Miyamoto I.,Osaka University | Cvecek K.,Bavarian Laser Center GmbH | Okamoto Y.,Okayama University | Schmidt M.,Bavarian Laser Center GmbH | Schmidt M.,Friedrich - Alexander - University, Erlangen - Nuremberg
Applied Physics A: Materials Science and Processing | Year: 2014

Internal modification process of glass by ultrashort laser pulse (USLP) and its applications to microwelding of glass are presented. A simulation model is developed, which can determine intensity distribution of absorbed laser energy, nonlinear absorptivity and temperature distribution at different pulse repetition rates and pulse energies in internal modification of bulk glass with fs- and ps-laser pulses from experimental modified structure. The formation process of the dual-structured internal modification is clarified, which consists of a teardrop-shaped inner structure and an elliptical outer structure, corresponding to the laser-absorbing region and heat-affected molten region, respectively. Nonlinear absorptivity at high pulse repetition rates increases due to the increase in the thermally excited free electron density for avalanche ionization. USLP enables crack-free welding of glass because the shrinkage stress is suppressed by producing embedded molten pool by nonlinear absorption process, in contrast to conventional continuous wave laser welding where cracks cannot be avoided due to shrinkage stress produced in cooling process. Microwelding techniques of glass by USLP have been developed to join glass/glass and Si/glass using optically contacted sample pairs. The strength of the weld joint as high as that of base material is obtained without pre- and post-heating in glass/glass welding. In Si/glass welding, excellent joint performances competitive with anodic bonding in terms of joint strength and process throughput have been attained. © 2013 Springer-Verlag Berlin Heidelberg.


Grant
Agency: European Commission | Branch: H2020 | Program: CSA | Phase: INFRADEV-1-2014 | Award Amount: 1.37M | Year: 2015

Challenges like climate change, economic, social and sustainable development as well as security are closely linked to the energy supply of European societies. In 2009, the European Union adopted a climate and energy package including that at least 20% of EU gross final energy consumption have to come from renewable energy sources until 2020. The challenge of RICAS2020 is given by intermittent renewable energy sources which require increased energy storage to time shift this energy to meet daily demand. As a consequence, the demand for technologies for providing and storing energy is consequently increasing. The RICAS2020 Design Study for the European Underground Research Infrastructure related to Advanced Adiabatic Compressed Air Energy Storage (AA-CAES) will provide concepts to set-up a research infrastructure dedicated to underground storage of very high amounts of green energy. The big advantage of the new concepts will be that the underground energy storage can be performed independently from the encountered geological conditions and also at all places where high energy demand exists. AA-CAES collects the heat produced by compression and returns it to the air when the air is expanded to generate power and thus delivers higher efficiencies via a zero-carbon process. The Design Study RICAS2020 will provide concepts on the key criteria and focus on technical, legal, institutional and financial requirements of such a research facility and will be open for the whole European Research Area, especially for all research fields close to Energy Providers and Suppliers. RICAS2020 will be located as an extension to the research infrastructure Research@ZaB in Eisenerz, Austria, which is financed by the Austrian government and designed as a European Underground Research-, Training- and Test-facility focussing on underground mobility including tunnels and subways. Synergies between RICAS2020 and Research@ZaB will be given in all underground technologies.


Weigl M.,Bavarian Laser Center GmbH | Schmidt M.,University of Erlangen Nueremberg
Physics Procedia | Year: 2010

The present article deals with the laser-welding of copper and stainless steel connections for applications in power electronics. Here, the particular demand for such dissimilar connections is caused by the increasing implementation of electronics in areas with contact to corrosive fluids, which copper cannot resist. In this context the influence of a lateral displacement of the laser beam and the feed rate on the metallurgical properties of the dissimilar materials' connection is highlighted. The effects of these parameters are discussed on the base of metallographic specimen, micro-hardness measurements and element analysis. © 2010 Published by Elsevier B.V.


Miyamoto I.,Osaka University | Cvecek K.,Bavarian Laser Center GmbH | Okamoto Y.,Okayama University | Schmidt M.,Bavarian Laser Center GmbH
Physics Procedia | Year: 2010

A novel fusion welding technology of glass using ultrashort laser pulses with high pulse repetition rates has been developed, where the laser energy is selectively absorbed at the interface by nonlinear process to provide crack-free welding without preand post-heating. A laser-matter interaction model is developed to evaluate the distribution of the ultrashort pulse laser energy absorbed in bulk glass. A thermal conduction equation is derived to calculate transient 3-dimensional temperature distribution and dimensions of molten zone in glass. The mechanical strength of weld joint is evaluated taking into consideration of the attracting force of the optical contact between the glass plates needed for keeping the high-temperature plasma in the bulk glass.


Weigl M.,Bavarian Laser Center GmbH | Albert F.,Bavarian Laser Center GmbH | Schmidt M.,Bavarian Laser Center GmbH | Schmidt M.,Friedrich - Alexander - University, Erlangen - Nuremberg
Physics Procedia | Year: 2011

Laser micro welding of direct copper-aluminum connections typically leads to the formation of intermetallic phases and an embrittlement of the metal joints. By means of adapted filler materials it is possible to reduce the brittle phases and thereby enhance the ductility of these dissimilar connections. As the element silicon features quite a well compatibility with copper and aluminum, filler materials based on Al-Si and Cu-Si alloys are used in the current research studies. In contrast to direct Cu-Al welds, the aluminum filler alloy AlSi12 effectuates a more uniform element mixture and a significantly enhanced ductility. © 2011 Published by Elsevier Ltd.


Kageler C.,Bavarian Laser Center GmbH | Schmidt M.,Bavarian Laser Center GmbH
Physics Procedia | Year: 2010

The movements of the keyhole and the weld pool at deep penetration solid-state laser welding can be analyzed by observing either the optical process emissions, or directly the work piece surface using camera systems in the visual range. In this paper, the welding process of zinc-coated steel sheets is monitored. The geometry and behaviour of weld pool and capillary are calculated from the acquired camera images, they are compared with the one-dimensional optical process emissions, and analyzed in the time- and frequency-domain. This helps to better understand the uncontrolled process behaviour, especially regarding the destructive influence of the evaporating zinc-layer. © 2010 Published by Elsevier B.V.

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