Femtosecond versus picosecond laser machining of nano-gratings and micro-channels in silica glass

Corbari, Costantino, Champion, Audrey, Gecevičius, Mindaugas, Beresna, Martynas, Bellouard, Yves and Kazansky, Peter G. (2013) Femtosecond versus picosecond laser machining of nano-gratings and micro-channels in silica glass. Optics Express, 21 (4), 3946-3958. (doi:10.1364/OE.21.003946).

Abstract

The ability of 8 picosecond pulse lasers for three dimensional direct-writing in the bulk of transparent dielectrics is assessed through a comparative study with a femtosecond laser delivering 600 fs pulses. The comparison addresses two main applications: the fabrication of birefringent optical elements and two-step machining by laser exposure and post-processing by chemical etching. Formation of self-organized nano-gratings in glass by ps-pulses is demonstrated. Differential etching between ps-laser exposed regions and unexposed silica is observed. Despite attaining values of retardance (>100 nm) and etching rate (2 µm/min) similar to fs pulses, ps pulses are found unsuitable for bulk machining in silica glass primarily due to the build-up of a stress field causing scattering, cracks and non-homogeneous etching. Additionally, we show that the so-called “quill-effect”, that is the dependence of the laser damage from the direction of writing, occurs also for ps-pulse laser machining. Finally, an opposite dependence of the retardance from the intra-pulse distance is observed for fs- and ps-laser direct writing.

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