Dynamic 193-nm optical properties of water

Previous assumptions that water is not a 193-nm chromophore during ArF excimer laser tissue ablation are based on room-temperature data and ignore spectroscopic literature that suggests a strong temperature dependence of far-ultraviolet water absorption. By the use of a Q-switched Er:YAG laser as a pump source and an ArF excimer laser as a probe source, thermal generation and relaxation of 193-nm water absorption were characterized under nonequilibrium high-temperature and highpressure conditions. At volumetric energy densities as small as 2 kJ/cm³ relative to room temperature, the 193-nm absorption coefficient of water was measured to increase by more than 5 orders of magnitude. These results are consistent with the hypothesis that the absorption of 193-nm radiation by water may play a role in ArF excimer laser ablation of tissue.