Laser polishing and 2PP structuring of inside microfluidic channels in fused silica

Abstract

This study presents the development of post-processing steps for microfluidics fabricated with selective laser etching (SLE) in fused silica. In a first step, the SLE surface-even inner walls of microfluidic channels—can be smoothed by laser polishing. In addition, two-photon polymerization (2PP) can be used to manufacture polymer microstructures and microcomponents inside the microfluidic channels. The reduction in the surface roughness by laser polishing is a remelting process. While heating the glass surface above softening temperature, laser radiation relocates material thanks to the surface tension. With laser polishing, the RMS roughness of SLE surfaces can be reduced from 12 µm down to 3 nm for spatial wavelength λ < 400 µm. Thanks to the laser polishing, fluidic processes as well as particles in microchannels can be observed with microscopy. A manufactured microfluidic demonstrates that SLE and laser polishing can be combined successfully. By developing two-photon polymerization (2PP) processing in microchannels we aim to enable new applications with sophisticated 3D structures inside the microchannel. With 2PP, lenses with a diameter of 50 µm are processed with a form accuracy rms of 70 nm. In addition, this study demonstrates that 3D structures can be fabricated inside the microchannels manufactured with SLE. Thanks to the combination of SLE, laser polishing and 2PP, research is pioneering new applications for microfluidics made of fused silica

Selective Laser-Induced Etching of 3D Precision Quartz Glass Components for Microfluidic Applications—Up-Scaling of Complexity and Speed

“…Thus, for any post-treatment the structure must be aligned again. However, post-treatments are only necessary for optical polishing needs since the surface finish after SLE is like a fine-grinded surface (peak-to-valley roughness Rz < 1 µm) and the alignment needs for subsequent laser polishing are minor [ 9 ]. Furthermore, we have demonstrated above that the missing in-line capability can be a clear advantage, especially for microfluidic applications: since the channels are present only after the etching, various post-processing methods such as mechanical sawing, grinding or milling can also be used after laser treatment without clogging the microchannels with dust particles.…”

Optimization of selective laser-induced etching (SLE) for fabrication of 3D glass microfluidic device with multi-layer micro channels

“…In the notion of three-dimensional (3D) channel structures enabling diverse applications upon intentionally designed complex flow characteristics, numerous 3D fabrication techniques such as multilayer bonding and stereo lithography have been explored [17][18][19]. Recently, ultrafast laser based 2-photon polymerization (TPP) has been demonstrated [20][21][22]. However, TPP can only fabricate 3D microstructures in liquid phase polymer or glassy materials, thus the strength of final structures is not as stiff as made from solid phase materials.…”

Chemical analysis using 3D printed glass microfluidics

“…[25][26][27][28] This method is especially suited for quartz glass, and its precision is high ($10 mm). 26 However, production is generally limited to relatively short channels ($20 mm), 26,27,29 but it is possible to increase the channel length by using additional vertical entrances for the etching reagent. 30 Manufacturing of small devices is also possible with femtosecond laser ablation, oen with the glass partly in water.…”