Mechanisms of femtosecond laser nanomachining of dielectric surfaces

Optical damage produced by femtosecond pulsed lasers on dielectric surfaces is extremely precise, allowing the damage mechanisms to be inferred from reproducible damage characteristics. Here nanoscale femtosecond laser ablation is applied to probe the ultrafast dynamics of laser energy deposition including the generation and transport of surface electron-hole or electron-ion plasmas. For shallow surface nano-craters fabricated on quartz and glass surfaces by single 0.53 mu m or 1.05 mu m laser shots, their corresponding well-defined laser intensity thresholds demonstrate pronounced effects of laser wavelength, crystalline state of the dielectric and laser waist radius, indicating equal importance of laser energy deposition and transport phenomena during ablation. Simultaneously, unusually deep surface nanoholes emerge drilled by self-focusing laser beam or forward-scattered highly penetrating short-wavelength radiation from the warm, dense surface plasma.