Pulsed CO₂ laser tissue ablation: Effect of tissue type and pulse duration on thermal damage

Tissue removal by infrared lasers is accompanied by thermal damage to nonablated tissue. The extent of thermal damage can be controlled by a choice of laser wavelength, irradiance, and exposure duration. The effect of exposure duration has been studied in vivo by using CO₂ lasers with pulse widths that vary from 2 μsec to 50 msec. Pulse widths of 50 msec, typical of a shuttered, continuous‐wave CO₂ laser, produce damage regions 750 μm wide in normal guinea pig skin; the use of a 2‐μseclong pulse reduced this damage zone to as little as 50 μm. Using 2‐μseclong pulses, in vitro studies showed that the minimum zone of thermal damage varied significantly with tissue type. The thermal denaturation of these tissues has been studied and correlated with damage. The effect of denaturation temperature and pulse duration on the width of the damage zone is explained by a simple model.