Nowadays, conventional glass processing techniques, such as “score and brake” method, are being replaced by laser-based techniques. Precision, speed and quality makes laser glass processing a very attractive technique for industry. However, new laser-based techniques have to be validated in respect to conventional processing. For this we introduce comparative investigation of free glass processing techniques – rear side laser cutting, laser-based and mechanical dicing. Local weakening of the material and mechanical separation is a highly efficient two-step glass cutting approach. Material modification can be introduced by laser or mechanically. However, when complex shape cutting is required rear side laser cutting can offer much more flexibility. Glass is a brittle material, therefore generation of micro-cracks during processing is inevitable. Such side-effects can influence processed surface quality and material flexural strength.
Rear side glass cutting experiments were carried out by tightly focusing the laser beam on the sample back-surface. Nanosecond laser pulses with wavelength of 532nm were used. In the case of laser glass dicing process, Bessel beam was introduced to form elongated modifications in glass. High pulse energy sub-nanosecond laser at 1064 nm wavelength was introduced. For mechanical processing, the conventional “score and break” method was used without any additional post processing. In all cases surface chipping was introduced. There was no significant difference in terms of micro-crack size for rear side cutting and mechanical dicing techniques. However, sample resistance to mechanical load was higher for mechanical processing. In this work, in-depth investigation of these effects will be introduced.
The generation of intra-volume modifications and mechanical separation is a highly efficient two-step glass cutting approach. The high aspect ratio modifications, required for thick glass cutting, can be obtained by utilizing Bessel-like beams, which have a long non-diffractive length with a small quasi-propagation-invariant central core. Usually, laser-induced modification channels have to be tightly spaced to achieve a predictable glass separation. However, we demonstrated that cutting speed and glass cleavability may be significantly enhanced by introducing aberrations to the generated beam.
Glass cutting experiments were carried out using the fundamental frequency of the DPSS laser Atlantic HE (from Ekspla), which delivered 300 ps pulses of 2 mJ energy at 1 kHz repetition rate. The incident Gaussian beam was reshaped to the Bessel-Gaussian beam using a conical lens and a 4F optical demagnifying system. A 4-point bending setup was used to separate glass sheets and to evaluate the processing regimes. We have found that the used conical lens deviated from an ideal cone shape and had two often occurring manufacturing defects - the oblate-tip and elliptical cross-section. As a result, the generated beam had the on-axis intensity modulations and asymmetrical intensity distribution in the XY plane, which induced transverse cracks in the bulk of glass, which were extended along the major axis of an ellipse-shaped central core of the beam. Laser-induced transverse cracks in combination with high aspect ratio modifications were applied for fast cutting of the 1 mm-thick glass. Results were compared to glass cutting using the symmetrical Bessel-Gaussian beam.
Conventional processing tools of glass cannot fulfil the forever increasing industrial requirements for processing speed and quality. In the future these methods can be replaced by emerging laser-based techniques. While nowadays most of the research is dedicated for thin, especially chemically strengthened glass, used in electronic devices, there is still a need for a suitable processing technique for thick glasses. One of the most material-efficient and energy-efficient glass cutting techniques is to locally weaken the material along the cutting path by generating cracks or material modifications and then separate sheets by applying thermal or mechanical load. Such approach provides a clean cut with an infinitely thin kerf width without a need for post-processing. Bessel-Gaussian beams, commonly generated using a conical lens, have very appealing properties for processing of transparent materials, such as the long non-diffractive propagation length and self-reconstruction. However, due to manufacturing tolerances, the shape of an optical element deviates from an ideal cone and the intensity pattern is non-symmetrical and modulated along the beam propagation axis. We have found that such asymmetry leads to the significant elongation of laser-induced glass cracks along one dominant direction, which can be beneficial for fast glass cutting.