Surface characteristics of alkaline earth boro-aluminosilicate glass following single picosecond laser pulse exposure at different focal positions

Abstract

We investigated the surface characteristics of alkaline earth boro-aluminosilicate glass (EAGLE XG, Coring), which is used in display applications, irradiated by a high power picosecond (ps, 10−12 s) pulsed laser beam while varying the position of focal position in and out of the top and bottom surfaces of the glass and the irradiation fluence of laser beam. Upon the single shot exposure of a 10 ps pulsed laser at the wavelength of 1064 nm, we found that laser processing of this type of glass is possible only near the surfaces above the certain threshold fluence high enough to cause enough multiphoton absorption. The processing threshold values were found to be 11 ± 2 and 7.1 ± 1.4 J/cm2 for 3.0 and 5.0 μJ excitation pulse energies corresponding to the intensities of 3.3 × 1012 and 5.5 × 1012 W/cm2, respectively. The morphological changes on the surfaces due to a single shot laser processing occurred until the focal position moved away from the surfaces about 10 μm outside of the glass at 3.0 μJ of pulse energy, which is longer than Rayleigh length. The distance that focal position moved inside of the glass to provide enough nonlinear absorption for laser processing on the surface increased several times compared to the cases of focal position moved outside. The distance also increased with increasing the pulse energy to 5.0 μJ. It was also found that the top surface was processed mainly by ablation with no significant melting at this fluence range and the bottom surfaces suffered considerable thermal damage such as melting and resolidification while no processing occurred deep inside of the glass further away from both the top and the bottom surfaces as the focal position moved from the top to the bottom surfaces. We expect that most of absorption occurs near the surface when the focal position is near the top surface while more absorption occurs inside of glass before the laser beam reaches the bottom surface when the focal position is near the bottom surface. Our single shot exposure results inspire some important insights on application of laser processing by ps pulses on glass type materials.