In-depth comparison of conventional glass cutting technologies with laser-based methods by volumetric scribing using Bessel beam and rear-side machining

Thick Glass High-Quality Cutting by Ultrafast Laser Bessel Beam Perforation-Assisted Separation

The cutting of thick glass is extensively employed in aerospace, optical, and other fields. Although ultrafast laser Bessel beams are heavily used for glass cutting, the cutting thickness and cutting quality need to be further improved. In this research, the high-quality cutting of thick glass was realized for the first time using ultrafast laser perforation assisted by CO2 laser separation. Initially, an infrared picosecond laser Bessel beam was employed to ablate the soda-lime glass and generate a perforated structure. Subsequently, a CO2 laser was employed to induce crack propagation along the path of the perforated structure, resulting in the separation of the glass. This study investigates the influence of hole spacing, pulse energy, and the defocusing distance of the picosecond laser Bessel beam on the average surface roughness of the glass sample cutting surface. The optimal combination of cutting parameters for 6 mm thick glass results in a minimum surface roughness of 343 nm in the cross-section.

Preparation of convex edges in fused silica by single pass perforation with a 2D Airy-Gaussian beam

Following ultrafast laser machining of fused silica, post-processing such as polishing and honing are typically required for edges. In this study, we employed a spatial light modulator (SLM) to generate the 2D Airy-Gaussian beam to prepare the convex edges in fused silica by using a single pass of a picosecond laser. It is found that, if the speed exceeds 5 mm/s, there would be plasma interference which is unfavorable for the separation process. A filament effect was observed when the internal laser peak power exceeds the damage threshold of fused silica. The shape of the convex edges was consistent with the propagation path of the 2D Airy-Gaussian beam inside the fused silica before separation. The inclination angle was 17° and 13°, respectively, on the upper and lower end of the edges. The results of this study provide a new, to our knowledge, method for the preparation of curved structures with different curvatures in transparent materials.

Femtosecond Laser Cutting of 110-550 µm Thickness Borosilicate Glass in Ambient Air and Water

The cutting quality and strength of strips cut with femtosecond-duration pulses were investigated for different thicknesses of borosilicate glass plates. The laser pulse duration was 350 fs, and cutting was performed in two environments: ambient air and water. When cutting in water, a thin flowing layer of water was formed at the front surface of the glass plate by spraying water mist next to a laser ablation zone. The energy of pulses greatly exceeded the critical self-focusing threshold in water, creating conditions favorable for laser beam filament formation. Laser cutting parameters were individually optimized for different glass thicknesses (110-550 µm). The results revealed that laser cutting of borosilicate glass in water is favorable for thicker glass (300-550 µm) thanks to higher cutting quality, higher effective cutting speed, and characteristic strength. On the other hand, cutting ultrathin glass plates (110 µm thickness) demonstrated almost identical performance and cutting quality results in both environments. In this paper, we studied cut-edge defect widths, cut-sidewall roughness, cutting throughput, characteristic strength, and band-like damage formed at the back surface of laser-cut glass strips.

Quality and flexural strength of laser-cut glass: classical top-down ablation versus water-assisted and bottom-up machining

The growing applicability of glass materials drives the development of novel processing methods, which usually lack comprehensive comparison to conventional or state-of-art ones. That is especially delicate for assessing the flexural strength of glass, which is highly dependent on many factors. This paper compares the traditional top-down laser ablation methods in the air to those assisted with a flowing water film using picosecond pulses. Furthermore, the bottom-up cutting method using picosecond and nanosecond pulses is investigated as well. The cutting quality, sidewall roughness, subsurface damage and the four-point bending strength of 1 mm-thick soda-lime glass are evaluated. The flexural strength of top-down cut samples is highly reduced due to heat accumulation-induced cracks, strictly orientated along the sidewall. The subsurface crack propagation can be reduced using water-assisted processing, leading to the highest flexural strength among investigated techniques. Although bottom-up cut samples have lower flexural strength than water-assisted, bottom-up technology allows us to achieve higher cutting speed, taper-less sidewalls, and better quality on the rear side surface and is preferable for thick glass processing.

Transversal and axial modulation of axicon-generated Bessel beams using amplitude and phase masks for glass processing applications

The control of laser-induced microcracks in the volume of transparent materials is essential for scribing processes. In this paper, we investigate the effect of various amplitude and single-level phase masks on both transverse and axial intensity distribution of the conventional axicon-generated Bessel beams. Furthermore, we demonstrate the volumetric crack control induced by an asymmetrical central core with an appropriately selected intensity level to avoid the influence of peripheral intensity maxima. Proper alignment of cracks and intra-distance between the modifications results in the reduced separation stress of the scribed samples. Furthermore, the additional amplitude modulation of the incident Gaussian beam is introduced to flatten the axial intensity distribution of the axicon-generated Bessel beam.

High Aspect Ratio Structuring of Glass with Ultrafast Bessel Beams

Controlling the formation of high aspect ratio void channels inside glass is important for applications like the high-speed dicing of glass. Here, we investigate void formation using ultrafast Bessel beams in the single shot illumination regime. We characterize the morphology of the damages as a function of pulse energy, pulse duration, and position of the beam inside fused silica, Corning Eagle XG, and Corning Gorilla glass. While a large set of parameters allow for void formation inside fused silica, the operating window is much more restricted for Eagle XG and Gorilla glass. The transient formation of a molten layer around voids enables us interpreting the evolution of the morphology with pulse energy and duration.