Laser technology has become an essential tool for material processing and offers significant advantages for overcoming limitations of different material processes. For example, the use of femtosecond lasers with ultrashort pulses and high maximum intensities enables the processing of transparent materials such as glass by non-linear process mechanism. This provides a more accurate and controlled energy delivery, which has the advantage of reducing heat-affected areas and thermal damage, as well as achieving accuracy up to the submicron range. It is ideal for processing sustainable materials such as glass for use in integrated sensors for lab-on-a-Chip or photonic devices. However, there are major differences in the fabrication and quality of waveguides based on different glass types and the laser parameters used. This work focuses on the study of volume processing in different glass materials, particularly comparing the direct writing of waveguides between BK7 borosilicate and fused silica glass. The inscribed micro-optical structures, including waveguides and beam splitters within the volume, were fabricated using a femtosecond NIR laser with 350 fs pulse duration in combination with a galvanometer scanner and a long focal length of 100 mm. We investigated the process stability and formation process for the inscription of waveguides in both glass types. By systematically changing laser parameters such as pulse energy, repetition rate and scan velocity the waveguide quality, continuity and properties of the refractive index change are shown comparing the processing regimes for borosilicate and fused silica glass in order to optimize the laser process parameters further.
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