München 2019 – scientific programme

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K: Fachverband Kurzzeit- und angewandte Laserphysik

K 7: Laser Applications II

K 7.5: Talk

Wednesday, March 20, 2019, 15:20–15:40, HS 3

Aperture-Controlled Paraxial Filtering of Ultrafast Laser Radiation for Contact-Free Surface Patterning of Dielectrics with Nanoscale Axial Precision — •Joachim Koch¹, Christof Schneider², Thomas Lippert², and Detlef Günther¹ — ¹Swiss Federal Institute of Technology, Laboratory of Inorganic Chemistry, ETH Zürich, Wolfgang-Pauli-Strasse 10, CH-8093 Zürich, Switzerland — ²Laboratory for Multiscale Materials Experiments, Paul-Scherrer-Institute, CH-5232 Villigen-PSI, Switzerland

We report on the prospects of near ultraviolet (NUV) ultrafast laser radiation for the surface patterning of dielectric materials with sub-100 nm axial precisions. A low Fresnel (F)-number optical sequence capable of projecting radiation with uniform intensity profiles across an objective lens’ image plane was conceived: It made use of an array of apertures, which served as paraxial cut-off filter to flatten the radiation intensity profile and to cancel out noise arising from Fourier spatial frequencies higher than 10⁴ m⁻¹. In this way, pattering of surface features practically free of tilt and bulge became possible.

Confocal microscopy on SrTiO₃ targets exposed to bursts of NUV laser pulses using irradiances of less or equal 10¹⁰ W/cm² revealed mid- to long-range axial precisions well below 100 nm. However, scanning electron microscopy indicated the formation of surface periodic structures, which occasionally limited the short-range axial precision to approximately half of the radiation’s wavelength. Theory essentials underlying the reported low F-number optical sequence are outlined and technical aspects about its design and applicability are discussed.