Effect of the pulse width on internal modification of diamond using an ultrashort-pulse laser

Diamond is considered a key material for next-generation electronics, yet controlling its internal modification for laser slicing remains challenging due to the material's extreme hardness and varying crystal quality. While previous studies have focused on process optimization, the fundamental interaction between laser parameters and material properties, specifically crystal quality and impurities, remains insufficiently understood. This study systematically investigates the influence of pulse width and impurity concentration on the formation mechanism of internal modified regions. We irradiated high-pressure high-temperature (HPHT) and chemical vapor deposition (CVD) single-crystal diamonds with varying nitrogen impurity levels, adjusting the pulse duration from the femtosecond to the picosecond regime. The investigation revealed a critical dependency of the modification morphology on the pulse regime. In the femtosecond domain, modifications manifested as discontinuous clusters, and their formation was not determined by the total impurity concentration. In contrast, the picosecond regime consistently produced continuous modified regions across all samples, independent of the synthesis method or defect density. We attribute this stability to thermal diffusion; the longer pulse duration facilitates energy transfer from the electron system to the lattice, inducing a uniform phase change that overrides localized defect effects. These findings demonstrate that picosecond pulses are useful for fabricating homogeneous and stable modified regions.