Non-thermal ablation characteristics of sapphire under deep UV and near IR femtosecond laser processing

The high precision microfabrication of hard, brittle transparent dielectrics, such as sapphire, remains fundamentally limited by residual thermal damage, even within the ultrafast laser regime. While femtosecond pulses are traditionally associated with cold processing, high-repetition-rate applications inevitably induce complex thermodynamic transitions that mask the intrinsic mechanisms of material removal. To circumvent these masking effects, this study establishes a comprehensive theoretical and experimental framework to investigate the wavelength dependent ablation dynamics of sapphire using deep ultraviolet and near infrared femtosecond lasers. Under the specific modeling conditions employed in this study, a condition-specific crossover frequency of approximately 400 kHz was identified as the onset of pronounced inter-pulse heat accumulation, and we systematically evaluate the divergent topological and structural evolutions driven by varying photon energies. Through advanced topographical and forensic microcharacterization, we isolate the fundamental hydrodynamic and stress propagation differences between volumetric multiphoton absorption and surface-localized interactions. Ultimately, this work elucidates the critical role of spatial energy confinement in suppressing catastrophic thermomechanical failure, providing vital physical insights and a strategic paradigm for the next generation of transparent dielectric micromachining.