Abstract: CO$-2$/ lasers are among the most important lasers used for medical applications such as laser surgery. This laser is used mainly for tissue cutting and tissue removal, exploiting the high power of this laser systems and the high absorption of the biological tissue at this laser wavelength. Our research continues earlier studies conducted at the Tel Aviv University since 1987 that come out with a theoretical model used for simulating tissue irradiated with a CO$-2$/ laser beam. When examining the previous studies on laser ablation we have found that the important mechanism of steam pressure ablation was neglected. Therefore in our work we added steam pressure ablation into the model and studied the effects of this new mechanism on the tissue irradiated with a CO$-2$/ laser. The simulations results reveal that top-hat beam profile (uniformly distributed intensity) produces less thermal damage and its ablation efficiency is higher compared with standard Gaussian beam profile. We saw that the efficiency of the steam pressure ablation process is considerably higher than the purely thermal ablation process. We also noticed that the layers underneath the tissue surface are responsible for the pressure ablation. !18
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