Thermal-feedback-controlled coagulation of egg white by the CO2 laser

Temperature feedback control during laser-assisted tissue coagulation was i nvestigated and demonstrated with the egg-white model. We observed the dyna mics of photothermal denaturation during CO, laser irradiation by simultane ously controlling surface temperature and monitoring He-Ne laser transmissi on of egg-white samples. Once a quasi-constant surface temperature was esta blished, transmission of egg white tended to decrease linearly with time. A nalysis of experimental data strongly suggested a first-order rate process. Since transmission was primarily affected by heat-induced increase in the scattering coefficient and depth of coagulation, we speculated that changes in transmission were reliable indicators of accumulating photothermal dama ge. Our experiments demonstrated that thermal feedback can effectively cont rol or limit photothermal damage. (C) 2001 Optical Society of America.