Temperature and thermal stress analysis of ultrashort laser processed glass

When glass absorbs high energy from ultrashort-pulsed lasers, a very rapid melting-cooling event occurs. Images taken by a Scanning Electron Microscope (SEM) reveal a surface feature which elucidates the glass is heated to above 2000 degrees C. A series of voids along the laser path is also observed and analyzed by SEM and High-angle Annular Dark-filed Scanning Transmission Electron Microscopy (HAADF-STEM). Molecular Dynamic simulation predicting observable voids in fused silica glass requires the temperature to be above 10,000 Kelvin. This suggests that the thermal effect from nonlinear absorption along cannot explain the void generation. Thermal stress analysis based on three different types of glasses revealed that stress generated by laser heating is highly correlated to thermal expansion coefficient. Such thermal stress may be a key factor for laser cutting.