Cutting of biological tissue underwater by CO₂ lasers. Using the 'cavitation effect

Another method for reducing the thermal damage is to find a way to cool the tissue. We were able to show that the thermal damage surroundign a crater made by a pulsed CO₂ laser may be reduced by irradiating the tissue under water. However, we first had to overcome the high absorption of the water layer. We used a pulsed laser beam of high energy and high repetition rate to create a stationary cavity in the liquid. Through this cavity the beam is transmitted to the material to be treated. Using a simplifid model, we found that the height of the cavity depends on the repetition rate and pulse energy of the beam but not on the pulse width. We also found that the temperature rise in the liquid surrounding the cavity increases with pulse width. In a series of experiments performed in bovine cornea, we found that the thermal damage surrounding the incision caused by a CO₂ laser beam was significantly reduced when the tissue was irradiated under water, applying the cavity mode of beam transfer.