Femtosecond laser-assisted etching of three-dimensional inverted-woodpile structures in fused silica

Three-dimensional inverted-woodpile (WP) structures were embedded in a microchannel by femtosecond laser direct-writing of fused silica followed by chemical etching with diluted hydrofluoric acid. We show the hole size is linearly dependent on laser-scanning depth for various pulse energies, permitting the control of laser exposures to facilitate close 5 µm periodic packing of uniform microcapillary arrays. Exposure compensation for depth-dependent etching rate and optical beam aberrations yielded stable and crack-free uniform inverted-WP structures. The direct formation of the inverted-WP structure together with microchannels in an all-fused silica substrate, offers chemical stability and inertness, and biocompatibility to be exploited as new microfluidic systems for chromatography and electro-osmotic pumps.