Single- and multi-scan femtosecond laser writing for selective chemical etching of cross section patternable glass micro-channels

We report on the fabrication of three dimensional micro-fluidic channels in fused silica glass using a combination of femtosecond laser writing and hydrofluoric acid wet etching to flexibly create various cross-sectional profiles of highly uniform shape and smooth vertical walls. The laser power, polarization, focusing depth, scanning angle and scanning speed were systematically studied with single- and multi-scan configurations to assess optimum micro-channel formation including etch rate, surface roughness, and stress-induced crack formation. We introduce the formation of vertical access-ports that extend the buried channel formation to unlimited length without tapering or distortion of the channel cross-sectional shape.