Adjustable multifocus laser separation scheme for thick glass with flexibly controllable thermal stress distribution

As a high-quality thick glass separation method, multifocus technology has proven its superiority. For a certain thickness of glass, there must be an optimal multifocus distance. But, the positions of the foci cannot be adjusted flexibly in current multifocus schemes without changing the energy proportions; the influence of thermal stress distribution on the quality of thick glass separation has not been systematically studied. An adjustable multifocus laser scheme has been proposed in this paper and proved by optical design, ray tracing, and experiment. First, finite element simulations have been performed to analyze the thermal stress distribution inside 20 mm glass. The simulation results show that thermal tensile stress exceeds the fracture threshold only at the upper and lower sides of the glass but not in the middle; the maximum thermal tensile stress reduces inside the glass when the symmetrical focal distance increases. Then, a series of separation experiments of 20, 22, and 25 mm thick soda lime glass have been carried out, which have adjusted foci positions to control the thermal stress distribution. The experimental results show that the deviation length decreases with an increase of the foci distances, and the optimal symmetrical foci distances reduce as the glass thickness increases.