Tomography of femtosecond laser structured objects inscribed in glass
Final Report Abstract
Processing of glass by ultra-short pulsed (USP) lasers found its way into many industrial applications such as glass welding for sealing applications in MEMS, cutting and drilling of displays or fabrication of microfluidic systems in medical devices. Moreover, laser micromachining using psor fs- lasers is already today considered to be a key enabling technologies for manufacturing of novel optical waveguides or next generation optical data storages. Unfortunately, the nature of laser-glass interaction is still barely understood and thus prediction of the characteristics of such structural modifications are hardly possible. The aim of the present research project was therefore to conduct basic research concerning the processes that take place during laser-matter interaction by linking spatially and temporally resolved analyses of laser-glass interaction with analyses of the thermodynamic state and chemical composition after the irradiation. In addition, lab-based X-ray microscopy (XRM) shall be used to provide quantitative three-dimensional data regarding the induced defect-structure and morphology. Different glass systems ranging from fused silica to soda-lime silicate and sodium germanate glass have been investigated to study the influence of ultra-short pulsed laser irradiation at 10 and 0.35 ps pulse duration on the glass network with or without additional network modifiers. The process dynamics and the resulting material modifications such as nanograting formation, gas bubble generation and glass network changes were observed by utilizing a broad range of specific imaging techniques. While high-speed optical imaging has been used to characterize the laserglass interaction dynamics by phase and amplitude observations, sophisticated 2D vibrational spectroscopy revealed a denser glass network under residual stress in the modified region of fused silica, when compared to the surrounding pristine glass. Similar results have been obtained for soda-lime silicates even though a higher adaption of the modified network compared the pure SiO2 network is indicated by the measurements. Cutting edge microstructure diagnostic using micro-XRF, cs-aberration-corrected transmission electron microscopy together with EDXS-analyses as well as time-of-flight secondary ion mass spectrometry (ToF-SIMS) could not detect any changes in composition particularly close to oxygen/gas bubbles generated via the laser-matter interaction. Since conventional workflows used for sample preparation for X-CT measurements showed some unexpected limitations, particularly in case of glasses, a novel workflow has been developed to select the specific site combined laser-micromachining using ps- or fs- lasers and mechanical polishing. Based on this, the shape and distribution of bubbles within laser modified zones was investigated quantitatively leading to new insights regarding the dynamics of bubble formation. This precise 3D analysis of the final microstructure of modified zones completed the dynamical 2D evolutions observed in situ by pump-probe interferometric method. Here, depending on the process geometry and known glass characteristics such as temperature dependence of the refractive index, a three-dimensional time dependent temperature distribution of the processing area has been estimated, from which cooling rates were determined and compared to results from the vibrational spectroscopy.
Publications
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Analysis of shockwave formation in glass welding by ultra-short pulses. Procedia CIRP 2018, 74, 339–343
Cvecek K.; Miyamoto I.; Heberle J.; Bergler M.; Ligny D. de; Schmidt M.
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On-line Interferometric Observation of Thermomechanically Induced Re-fractive Index Changes during Glass Welding by Ultra-short Laser Pulses. J. Laser Micro Nanoeng., 2018, 13, 301–308
Cvecek K.; Heberle J.; Miyamoto I.; Bergler M.; Ligny D. de; Schmidt M.
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Cooling rate calibration and mapping of ultra-short pulsed laser modifications in fused silica by Raman and Brillouin spectroscopy. Int. J. Extrem. Manuf., 2020, 2, 35001
Bergler M.; Cvecek K.; Werr F.; Brehl M.; Ligny D. de; Schmidt M.
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Coupling raman, brillouin and Nd3+ photo luminescence spectroscopy to distinguish the effect of uniaxial stress from cooling rate on soda-lime silicate glass. Mater., 2021, 14, 3584
Bergler M.; Cvecek K.; Werr F.; Veber A.; Schreiner J.; Eckstein U.R.; Webber K.G.; Schmidt M.; Ligny D. de
