Internal silicon laser processing with picosecond double pulses

Nonlinear propagation effects present major challenges for inscription inside silicon using ultrashort laser pulses. To overcome these limitations, we employ single-digit picosecond double pulses with picosecond pulse-to-pulse delays, enabling repeatable in-volume modifications. The double-pulse benefits are most pronounced for temporally separated pulses with perpendicular polarization. In contrast, interference caused by temporally overlapping pulses with parallel polarization has a catastrophic impact on in-volume modification. Both energy deposition efficiency and modification size are controlled by adjusting the energy balance between the two pulses and the total energy. Double-pulse irradiation offers a promising approach for precise internal functionalization of silicon.