19 February 2018 Nano- and micro-structuring of fused silica using time-delay adjustable double flash ns-laser radiation
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Large area, high speed, nanopatterning of surfaces by laser ablation is challenging due to the required high accuracy of the optical and mechanical systems fulfilling the precision of nanopatterning process. Utilization of self-organization approaches can provide an alternative decoupling spot precision and field of machining. The laser-induced front side etching (LIFE) and laser-induced back side dry etching (LIBDE) of fused silica were studied using single and double flash nanosecond laser pulses with a wavelength of 532 nm where the time delay ∆τ of the double flash laser pulses was adjusted from ∼50 ns to ∼10 μs. The fused silica can be etched at both processes assisted by a 10 nm chromium layer where the etching depth ∆z at single flash laser pulses is linear to the laser fluence and independent on the number of laser pulses, from 2 to 12 J/cm2, it is ∆z = δLIFE/LIBDE ⋅ Φ with δLIFE ∼ 16 nm/(J/cm2) and δLIBDE ∼ 5.2 nm/(J/cm2) ∼ 3 ⋅ δLIFE. At double flash laser pulses, the ∆z is dependent on the time delay ∆τ of the laser pulses and the ∆z slightly increased at decreasing ∆τ. Furthermore, the surface nanostructuring of fused silica using IPSM-LIFE (LIFE using in-situ pre-structured metal layer) method with a single double flash laser pulse was tested. The first pulse of the double flash results in a melting of the metal layer. The surface tension of the liquid metal layer tends in a droplet formation process and dewetting process, respectively. If the liquid phase life time ∆tLF is smaller than the droplet formation time the metal can be "frozen" in an intermediated state like metal bare structures. The second laser treatment results in a evaporation of the metal and in a partial evaporation and melting of the fused silica surface, where the resultant structures in the fused silica surface are dependent on the lateral geometry of the pre-structured metal layer. A successful IPSM-LIFE structuring could be achieved assisted by a 20 nm molybdenum layer at ∆τ ≥ 174 ns. That path the way for the high speed ultra-fast nanostructuring of dielectric surfaces by self-organizing processes. The different surface structures were analyzed by scanning electron microscopy (SEM) and white light interferometry (WLI).
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Pierre Lorenz, Pierre Lorenz, Xiongtao Zhao, Xiongtao Zhao, Martin Ehrhardt, Martin Ehrhardt, Igor Zagoranskiy, Igor Zagoranskiy, Klaus Zimmer, Klaus Zimmer, Bing Han, Bing Han, "Nano- and micro-structuring of fused silica using time-delay adjustable double flash ns-laser radiation", Proc. SPIE 10520, Laser-based Micro- and Nanoprocessing XII, 105201K (19 February 2018); doi: 10.1117/12.2288294; https://doi.org/10.1117/12.2288294

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