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Proceedings Paper

Automated pump-probe microscope to observe laser ablation on a picosecond scale
Author(s): Fabian Meyer; Mario Böhler; Andreas A. Brand; Jan F. Nekarda
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Paper Abstract

Pump-probe microscopy is a well suited tool to follow the highly dynamic phenomena during laser material processing on a picosecond to microsecond scale. We present a pump-probe microscope, to monitor the phase and morphology of the silicon-dielectric interface during and after irradiation with focused high-intensity laser pulses. Laser ablation with ultrashort pulses is used to locally structure dielectric layers for contact formation on the surface of silicon solar cells. With the pump-probe microscope we can study the dynamics and the physical mechanisms of the local ablation process. A mode-locked 180 fs laser is used to illuminate the sample through a microscope objective at a wavelength of 515 nm. The same laser can be used to locally ablate the thin dielectric layer on the silicon substrate. The delay between ablation pulse (pump) and illumination pulse (probe) can be adjusted using an optical delay line with sub-picosecond precision. Alternatively other pump laser sources have been integrated using timing electronics and photodiodes, with a temporal resolution of around 1 ns. Because the system is fully automated, we can collect a large number of transient reflectance images at different points in time, which can then be combined to form a consistent video of the process. With a temporal resolution of 0.2 ps, we find a fast increase in reflectance due to melting of the surface at the beginning of the process. As the removal of the topmost layer begins, newton rings can be observed and evaluated to reconstruct the surface.

Paper Details

Date Published: 21 June 2019
PDF: 6 pages
Proc. SPIE 11056, Optical Measurement Systems for Industrial Inspection XI, 110561V (21 June 2019); doi: 10.1117/12.2525709
Show Author Affiliations
Fabian Meyer, Fraunhofer-Institut für Solare Energiesysteme (Germany)
Mario Böhler, Fraunhofer-Institut für Solare Energiesysteme (Germany)
Andreas A. Brand, Fraunhofer-Institut für Solare Energiesysteme (Germany)
Jan F. Nekarda, Fraunhofer-Institut für Solare Energiesysteme (Germany)

Published in SPIE Proceedings Vol. 11056:
Optical Measurement Systems for Industrial Inspection XI
Peter Lehmann; Wolfgang Osten; Armando Albertazzi Gonçalves Jr., Editor(s)

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