Sub-50-femtosecond gain-managed amplified pulses enhance nonlinear ablation efficiency.

Nonlinear femtosecond (fs) laser ablation enables highly localized energy deposition for cell microsurgery. Conventional systems operate at either low (∼1 kHz, amplified µJ pulse energy) or high (∼80 MHz, unamplified low nJ) repetition rates, but intermediate rates with amplified pulse energy offer a promising balance of ablation speed and thermal control. We custom-built a low-cost, 32 MHz femtosecond fiber laser system with gain-managed nonlinear amplification, boosting pulse energy from 5 to 90 nJ while compressing pulse duration to 46 fs. In this intermediate-repetition-rate regime, the use of sub-50-fs pulses enhances ablation efficiency by strengthening multiphoton absorption and lowering the effective ablation threshold, while also leveraging multi-pulse incubation effects that promote cumulative energy deposition at reduced per-pulse energies. Compared to 200-500 fs pulses typically used for ablation, shorter durations double ablation efficiency in silicon and yield a ∼10× increase in cell membrane damage. In 3D tumor models, this approach enables targeted subsurface ablation up to 400 µm depth with 6 nJ pulse energy. These results inform the design of next-generation femtosecond laser systems for microsurgery.