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Probing timescales during back side ablation of Molybdenum thin films with optical and electrical measurement techniques

: Bartl, Dominik; Ametowobla, M.; Schmid, F.; Letsch, Andreas; Hafner, Margit; Nolte, Stefan; Tünnermann, Andreas

Postprint (PDF; )

Optics Express 21 (2013), No.14, pp.16431-16443
ISSN: 1094-4087
Journal Article, Electronic Publication
Fraunhofer IOF ()
application examples; electrical measurement techniques; laser fluences; maximum velocity; measurement technique; test structure; time-dependent currents; transparent substrate

In this study we present a new measurement technique to investigate the timescales of back side ablation of conductive films, using Molybdenum as an application example from photovoltaics. With ultrashort laser pulses at fluences below 0.6 J/cm2, we ablate the Mo film in the shape of a fully intact Mo 'disc' from a transparent substrate. By monitoring the time-dependent current flow across a specifically developed test structure, we determine the time required for the lift-off of the disc. This value decreases with increasing laser fluence down to a minimum of 21±2 ns. Furthermore, we record trajectories of the discs using a shadowgraphic setup. Ablated discs escape with a maximum velocity of 150 ± 5 m/s whereas droplets of Mo forming at the center of the disc can reach velocities up to 710±11 m/s.