Universität Stuttgart
Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1
Browse
4 results
Search Results
Item Open Access Determination of the thermally induced focal shift of processing optics for ultrafast lasers with average powers of up to 525 W(2018) Faas, Sebastian; Förster, Daniel J.; Weber, Rudolf; Graf, ThomasThe continuous increase of the average laser power of ultrafast lasers is a challenge with respect to the thermal load of the processing optics. The power which is absorbed in an optical element leads to a temperature increase, temperature gradients, changing refractive index and shape, and finally causes distortions of the transmitted beam. In a first-order approximation this results in a change of the focal position, which may lead to an uncontrolled change of the laser machining process. The present study reports on investigations on the focal shift induced in thin plano-convex lenses by a high-power ultra-short pulsed laser with an average laser power of up to 525 W. The focal shift was determined for lenses made of different materials (N-BK7, fused silica) and with different coatings (un-coated, broadband coating, specific wavelength coating).Item Open Access Estimation of the depth limit for percussion drilling with picosecond laser pulses(2018) Förster, Daniel J.; Weber, Rudolf; Holder, Daniel; Graf, ThomasItem Open Access Influence of pulse duration on X-ray emission during industrial ultrafast laser processing(2022) Holland, Julian; Weber, Rudolf; Sailer, Marc; Graf, ThomasSoft X-ray emissions during the processing of industrial materials with ultrafast lasers are of major interest, especially against the background of legal regulations. Potentially hazardous soft X-rays, with photon energies of >5 keV, originate from the fraction of hot electrons in plasma, the temperature of which depends on laser irradiance. The interaction of a laser with the plasma intensifies with growing plasma expansion during the laser pulse, and the fraction of hot electrons is therefore enhanced with increasing pulse duration. Hence, pulse duration is one of the dominant laser parameters that determines the soft X-ray emission. An existing analytical model, in which the fraction of hot electrons was treated as a constant, was therefore extended to include the influence of the duration of laser pulses on the fraction of hot electrons in the generated plasma. This extended model was validated with measurements of H (0.07) dose rates as a function of the pulse duration for a constant irradiance of about 3.5 × 1014 W/cm2, a laser wavelength of 800 nm, and a pulse repetition rate of 1 kHz, as well as for varying irradiance at the laser wavelength of 1030 nm and pulse repetition rates of 50 kHz and 200 kHz. The experimental data clearly verified the predictions of the model and confirmed that significantly decreased dose rates are generated with a decreasing pulse duration when the irradiance is kept constant.Item Open Access Scaling the productivity of laser structuring processes using picosecond laser pulses at average powers of up to 420W to produce superhydrophobic surfaces on stainless steel AISI 316L(2019) Faas, Sebastian; Bielke, Uwe; Weber, Rudolf; Graf, Thomas