Material ejection in free-running Er:YAG laser ablation of water, liver, and skin

We investigated the mechanisms of material ejection in IR laser tissue ablation using free-running Er:YAG laser pulses. We found that for water and soft tissues such as liver the primary mechanism for material ejection is a phase explosion within the target material. The recoil induced by the primary material ejection causes a secondary material expulsion that largely increases the ablation efficiency. For mechanically stronger tissues such as skin, the material ejection is driven by confined boiling, and recoil-induced expulsion plays no role. The high efficiency of recoil-induced material expulsion is associated with a loss in ablation precision and an increase of mechanical side effects that needs to be considered for an appropriate choice of laser parameters.