Modeling laser texturing of silicate glass

A refined model of a glass laser texturing process used on computer disk substrates is presented. Field equations for fictive temperature and elasto-viscoplastic strain in the glass are numerically integrated over the thermal cycle created with a microsecond CO2 laser pulse. Calculating the fictive temperature change as part of the solution provides for a consistent treatment of glass properties that depend on fictive temperature. The short time scale of the thermal cycle causes the final altered state of fictive temperature in the heat affected zone to be relatively constant over the depth of change, and higher than the initial value by more than 300 K. Plastic strain resulting from thermomechanical stresses and the fictive temperature rise are considered in this description. The model illustrates the rise in the compressive stress caused by initial heating, the relaxation process that occurs in the molten region above the transition temperature, and the subsequent introduction of tensile stress during cooling. At the end of the thermal cycle, the region of glass with altered fictive temperature is left in a state of high tensile stress. The time evolution of surface topography is studied with the model, and shows good agreement with measured dimensions of the final bump geometry over a range of laser pulse energies. (C) 2001 American Institute of Physics.