How far does thermal damage extend beneath the surface of CO2 laser incisions?

One of the principal advantages of the CO2 surgical laser over other types available is that there is little evidence of thermal injury extending very far beyond the surface of the laser wound. The degree of such damage is of interest because it affects tissue healing and the likelihood of post-operative infection. This paper presents a simple physical model of tissue irradiated by a CO2 laser beam. The depth of damage is predicted for the case where the ablation front and the damage wave ahead of it advance together at the same speed. The depth of damage is also calculated for the case of laser pulses of short duration where there has not been time to establish dynamic equilibrium. The results are plotted against local laser power density and show a trend of narrower damage depths with short laser pulses and high power densities. As a consequence, care should be taken not to ablate tissue at low power densities, as occurs when the laser beam is defocussed. The predicted damage depths are in broad agreement with histopathological experience.