The role of plasma in ablation of materials by ultrashort laser pulses

The ablative formation of deep channels in steel by femtosecond and picosecond laser pulses is studied. A significant screening of the incident energy inside deep channels is found to occur due to the air breakdown at ablated microparticles. The breakdown thresholds and the microparticle precipitation times are estimated. This kind of plasma screening stabilises the linear ablation rate and causes a significant channel broadening.