Material Modification of Borofloat 33 During Scanning‐Based Microforming Using Femtosecond Laser Pulses

Processing transparent materials with ultrashort laser pulses (USP) provides significant advantages over conventional methods in various industrial applications, enabling precise energy deposition and controlled modification of the laser irradiated material. The present study investigates ablation‐free surface structuring (microforming) of borosilicate glass (Borofloat 33, SCHOTT) using USP‐laser (350 fs at a wavelength of 515 nm) in a scanning‐based laser process. Irradiated areas ranged from 1 to 12 mm, with microformed structures produced on both top and bottom sample surfaces, reaching profile heights (peak‐to‐valley) of up to 20 µm. The analysis focuses on the relationship between temporal and spatial energy distribution and the ultra‐fast cooling rate during USP laser treatment. It was found that ablation‐free microforming is determined by the scanning strategy, the amount of energy absorbed, and the interaction volume, with the critical energy threshold for glass softening identified as crucial for controlled structuring. Characterization by white light interferometry, polarimetry, wavefront analysis, Raman spectroscopy, and thermography revealed structural changes in the glass network, including inhomogeneous density changes, measurable volume expansion within the irradiated areas and non‐homogeneous residual stress distributions. These effects are found to be responsible for the formation of the modified surface topography.