Top view pump-probe images at different significant delay times (left upper corner of every image) of 100 nm (top two rows) and 300 nm (lower two rows) Ta2O5 on 200 nm Pt ablated with a 1053 nm/660 fs (FWHM) pulse at a pulse peak fluence of ? = 0.2 J/cm2.
Top view pump-probe images at different significant delay times (left upper corner of every image) of 100 nm (top two rows) and 300 nm (lower two rows) Ta2O5 on 200 nm Pt ablated with a 1053 nm/660 fs (FWHM) pulse at a pulse peak fluence of ? = 0.2 J/cm2.

Maskless patterning of biocompatible Ta2O5/Pt/glass sensor chips can be realized by ultra-short laser pulse ablation. At a fluence of 0.2 J/cm2, the thin Ta2O5 film is selectively lifted-off by indirectly-induced ablation at laser wavelenghts where the Ta2O5 is transparent and the Pt absorbing. This enables precise and very fast structuring. Here, 660 fs laser pulses at a center wavelength of 1053 nm are applied. The driving physical effects of this ablation mechanism are revealed by pump-probe microscopy. This technique allows the observation of the whole ablation process ranging temporally from femtoseconds to microseconds. An ultrafast heat-expansion in the absorbing Pt, initiating a shock-wave to the Ta2O5 within the first 10 ps, bulges the Ta2O5 film after some nanoseconds. Bulging velocities of 750 m/s are determined corresponding to an extreme acceleration of about 1010 g. Exceeding the stress limit in the Ta2O5 causes film disintegration after 50 ns. A model, describing essential reaction steps, is developed. This model is also applicable to other industrial important layer systems, where thin transparent films have to be removed.

This paper was originally published in Applied Surface Science 290 (2014) Pages 368-372.

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