Erlangen 2022 – wissenschaftliches Programm
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K: Fachverband Kurzzeit- und angewandte Laserphysik
K 6: Laser-Beam Matter Interaction - Laser Applications I
K 6.5: Vortrag
Donnerstag, 17. März 2022, 11:45–12:00, K-H4
The Fluence-Dependent Transient Reflectance of Stainless Steel Investigated by Ultrafast Imaging Pump-Probe Reflectometry — •Theo Pflug1, Markus Olbrich1, Jan Winter2, Jörg Schille1, Udo Löschner1, Heinz Huber2, and Alexander Horn1 — 1Laserinstitut Hochschule Mittweida, Mittweida, Deutschland — 2Hochschule München, München, Deutschland
The ablation efficiency during laser processing strongly depends on the initial and transient reflectance of the irradiated material surface. This work reports on the transient relative change of the reflectance ΔR/R of stainless steel during and after ultrashort pulsed laser excitation (800 nm, 40 fs) by spatially resolved pump-probe reflectometry. The spatial resolution of the setup in combination with the spatial Gaussian intensity distribution of the pump radiation enables a fluence-resolved detection of ΔR/R. Within the first picosecond after irradiation with a peak fluence of 2 J/cm2, the spatially resolved ΔR/R of stainless steel evolves into an annular shape, in which the center almost remains at its initial reflectance, whereas the outer region features a decreased reflectance. The decreasing trend of ΔR/R is qualitatively supported by applying a two-temperature model, considering the transient optical properties of stainless steel from the literature. At larger fluences and thus higher electron temperatures, the experimental data deviates from the transient reflectance given in the literature. A decreased occupation of the states below the Fermi energy and the subsequent excitation of electrons into these new vacant states by the probe radiation is considered as the most probable origin for this behavior.