Low thermal damage cutting of tissue using high irradiance CW CO₂ laser radiation

Tissue cutting experiments were performed using freshly harvested guinea pig skin and bovine cornea and high-irradiance CW CO₂ laser radiation. The object is to minimize the damage by having the velocity of the ablation front exceed the velocity of the advancing thermal wave. The irradiance was varied from 0.2 to 800 kW/cm². Both isolated holes and linear incisions were made. Grossly, black char was seen only at irradiances of <6 kW/cm²; in skin a slight brown discoloration of the otherwise white tissue was noted at higher irradiances. Histologically, the zone of damage was typically 100 ± 15 μm in width at irradiances of >13 kW/cm². Mass-loss measurements indicate a heat of ablation of 4.8 kJ/cm³ and show a dependence of the heat ablation on spot size. The results indicate that the thermal damage produced by existing clinical CO₂ lasers can be reduced to ~100 μm by using high-irradiance radiation.