| Abstract [eng] |
This dissertation focuses on the investigation of the etching selectivity in bulk fused silica modified with ultrashort laser pulses and fabrication of the complex 3D microfluidic devices. Here, the combination of a few topics is presented. The femtosecond laser-induced chemical etching technique (FLICE) was used for microchannels inscription in bulk fused silica. The broad range of the highly focused femtosecond pulses parameters was investigated for optimizing the microchannels etching rate. It was demonstrated that the optimal etching conditions were achieved for the channels fabricated with the multipulse irradiation and pulse duration exceeding ~ 700 fs. Microchannels inscribed with the tightly focused pulses of the 1030 nm wavelength showed ~ 20% better etching performance comparing to the 515 nm wavelength pulses. The etching selectivity was induced due to the volume nanostructures that were oriented perpendicularly to the laser beam polarisation. The nature of the nanogratings is not completely understood thus this phenomenon is under debate. By investigating the morphology of such nanogratings with the SEM microscope, it has been observed that the orientation of the nanogratings was slightly tilted with respect to the scan direction. This remark followed the discovery of the new phenomenon that demonstrated the nanogratings tilt dependence on the different scanning directions when laser polarisation was kept constant. The phenomenon was investigated under the different laser radiation parameters, and a theoretical model was proposed. It was demonstrated enhanced etching of the structures fabricated with the contour scanning method in combination with the linear or circular polarisation which also followed the minimized surface roughness (Ra~ 75 nm) of the microchannels fabricated with the optimal 200 nJ pulse energy and ~ 1 mm/s scanning speed. The practical applications of the FLICE technique were demonstrated by fabricating three different 3D microfluidic devices for fluid pumping, microchannels for ellipsometric application and challenging double-sided aspheric microfluidic lens for light focusing from the Y-shaped waveguide. |
