CC BY
13LMI-O-2
Time-resolved pump-probe microscopy of the complete ablation dynamics in ultrashort laser pulse irradiated aluminum and stainless steel
J. Winter1,2, S. Rapp1, M. Spellauge1, M. Schmidt2, H.P. Huber1
1Lasercenter Munich University of Applied Sciences, Department of Applied Sciences and Mechatronics, Munich, Germany
2Friedrich-Alexander University Erlangen-Nurnberg, Erlangen, Germany; Institute of Photonic Technologies, Erlangen, Germany
Metals irradiated with ultrashort laser pulses pass through a sequence of physical processes that occur over a wide range of timescales, from femtoseconds to microseconds. The complete laser ablation process for the industrially relevant metals, aluminium (Al) and stainless steel (AISI 304) is tracked from the initial pulse absorption to the material removal occurring on a microsecond time scale.
The time-resolved ellipsometry [1,2] reveals changes in the real and imaginary part of the refractive index for the first tens of picoseconds and complementary time-resolved microscopy [3] gives access to changes of the relative reflectivity from the initial femtosecond pulse impact to the final state at 10 p,s. The changes in optical indices imply an ultrafast decrease [2] in the density connected to the pressure unloading process in the first picoseconds and reveal spallation as the dominant mechanism for laser ablation in bulk Al and stainless steel at the applied fluences. The study demonstrates that the energy specific ablation volume is kept at an optimum when the ablation is initiated with ultrafast pulses within the pressure unloading process and is able to evolve over eight orders of magnitude without perturbation from subsequent pulses to the final state. These results advance our understanding of a key aspect of the laser-material interaction pathway and can lead to optimization of associated applications ranging from material processing to laser surgery.
References
[1] S. Rapp, M. Kaiser, M. Schmidt, H. P. Huber, Ultrafast pump-probe ellipsometry setup for the measurement of transient optical properties during laser ablation, Opt. Express 24 (2016) 17572.
[2] J. Winter, S. Rapp, M. Schmidt, H. Huber, Ultrafast laser processing of copper: A comparative study of experimental and simulated transient optical properties, Appl. Surf. Sci. 417 (2017) 2-15.
[3] M. Domke, S. Rapp, M. Schmidt, H. P. Huber, Ultrafast pump-probe microscopy with high temporal dynamic range, Opt. Express 20 (2012) 10330-10338.
