Dynamic all-optical control in ultrashort double-pulse laser ablation

Abstract

Double-pulse femtosecond laser ablation of thin aluminum films and bulk aluminum counterintuitively demonstrated a strong (60–70%) raise of the thickness-dependent thresholds for inter-pulse delays of 20–200 ps, preventing material removal at above-threshold fluencies. Time-resolved optical pump-probe reflection and double-pump transmission studies were performed and confirmed the variation of the ablation threshold depending on the interpulse delay. To support the experimental measurements, the process of double-pulse laser ablation was modelled with the combined atomistic-continuum model. The applied model can describe the laser-induced non-equilibrium phase transition processes at atomic precision, whereas the effect of free carriers, playing a determinant role for the case of ultrashort laser pulses, is accounted for in the continuum. The simulations revealed the underlying pre-ablative laser-induced stress dynamics in the hot, acoustically relaxed Al melt, crucially sensitive to the second pump-pulse compressive pressurization. The results of theoretical and experimental study enable efficient dynamic all-optical control of ultrafast laser ablation.