Tissue ablation by a free-electron laser tuned to the amide II band

EFFORTS to ablate soft tissue with conventional lasers have been limited by collateral damage and by concern over potential photochemical effects1–5. Motivated by the thermal-confinement model6, past infrared investigations targeted the OH-stretch mode of water with fast pulses from lasers emitting near 3,000 nm (refs 1, 7–9). What does a free-electron laser offer for the investigation of tissue ablation? Operating at non-photochemical single-photon energies, these infrared sources can produce trains of picosecond pulses tunable to the vibrational modes of proteins, lipids and/or water. We report here that targeting free-electron laser radiation to the amide II band of proteins leads to tissue ablation characterized by minimal collateral damage while maintaining a substantial ablation rate. To account for these observations we propose a novel ablation mechanism based on compromising tissue through resonant denaturation of structural proteins.