Investigations on laser induced plasma upon high-intensity double pulse laser material processing

• Applicant: Professor Dr. Alexander Horn
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas ; Experimental Condensed Matter Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 538140778

Material processing with ultrashort-pulsed laser radiation can generate an ablation plume consisting out of vapour and ionized particles, especially when using multipulses with high power densities. For simplification, this mixture is referred to as plasma in this project proposal, regardless of the degree of ionization. At high pulse repetition frequencies, this plasma interacts on the one hand with the subsequent pulses (plasma-laser radiation interaction), and on the other hand subsequently heats the material surface after the irradiation, and thus causes additional thermomechanical stresses and shock waves within the remaining material (plasma-material interaction). Decisive for the plasma-laser interaction are the transient optical properties (reflectance, transmittance and absorbance) as well as the geometry of the expanding plasma. The plasma-material interaction is mainly determined by the temperature of the plasma. This project characterizes the physical processes during the material excitation and the subsequent formation and expansion of a laser-induced plasma by means of imaging pump-probe reflectometry, plasma spectroscopy and interferometry after single- and double-pulse irradiation. The focus lies on the transient optical properties of the laser-induced plasma, its effect on subsequent pulses depending on the temporal delay and lateral distance of these pulses, and the thermomechanical effect of the plasma on the material surface left behind. These properties cannot be fully characterized with the existing pump-probe metrology of the Horn research group (imaging pump-probe reflectometry and ellipsometry), since it does not provide information about the spectral emission and absorption properties of the plasma and their geometric distribution. Therefore, in addition to the existing pump-probe reflectometry setup, a DFG-funded imaging spectrograph in combination with an emICCD camera is used in this project. The addition of the funded spectrograph to the existing measurement equipment will allow a comprehensive investigation of the above processes, which are both technically and scientifically relevant. The measured experimental data will be used to directly derive insights for determining suitable parameter windows for more efficient material processing (technical objective). Through the comprehensively detected transient optical properties of the plasma, existing theoretical models (two-temperature hydrodynamics) for the description of the laser radiation-matter interaction shall be further developed, extended and validated in order to increase the understanding of the plasma-laser radiation interaction and plasma-matter interaction (scientific objective).

• DFG Programme: Research Grants