Theo Pflug

Hochschule Mittweida - University of Applied Sciences
Laserinstitut Hochschule Mittweida

Forschungsgruppe „Dynamik ultraschneller selektiver Laserprozesse“

email: pflug@hs-mittweida.de

Abstract:

Interferometry allows to measure microscopic displacements in the nanometer scale. This work introduces an imaging pump-probe interferometer that enables to detect the spatially resolved phase shift of the probe radiation being reflected on a sample surface after ultrashort pulsed laser excitation with a temporal resolution of 40 fs and a maximum temporal delay of 3 ns. The capability of the pump-probe interferometer is demonstrated on the spallation of a thin gold film upon femtosecond laser irradiation. The pump-probe interferometer enables to measure a minimum phase change of φ<π/10 which corresponds to a displacement of h< 12.5 nm for the applied probe wavelength of 500 nm. Upon irradiation, two distinct phase changes are observable: First, an abrupt minor phase shift has been measured in the femtosecond range, which is attributed to the changed optical properties of the sample surface after excitation. Second, a more pronounced continuing phase shift increase is detectable after a few tens of picoseconds resulting from the onset of spallation. Based on the measured spatially resolved phase shift, the transient surface topography during the spallation is reconstructed. The determined velocity of the ablated material reaches a maximum of a few 1000 m/s at ten picosecond after irradiation and decreases to 250 m/s afterwards. Consequently, the introduced imaging pump-probe interferometer provides important insights into the physical processes during laser excitation as well as the subsequent laser-induced ablation, and will enable to validate theoretical models quantitatively in following studies.

Short bio:

Theo Pflug is a System Engineer at the Carl Zeiss SMT GmbH. Previously, he has been investigating the ultrafast dynamics during the interaction of laser radiation with matter at the Laserinstitut Hochschule Mittweida by applying spatially resolved pump-probe ellipsometry and interferometry. He received his doctoral degree in Experimental Physics from Chemnitz University of Technology in 2022.