Ablation rate and threshold flux of cartilage irradiated by a XeCl excimerlaser

Results are presented related to the ablation of animal cartilage by a XeCl laser beam (308 nm). In particular the minimum energy flux for ablation an d the ablation rate as a function of the energy flux were measured. The eff ect of the pulse repetition rate on the cartilage temperature and the influ ence of a flowing cooling gas were also investigated. A new method, based o n the observation of the acoustic wave produced during the ablation process and the delay of arrival of the wave to the back of the sample with respec t to the laser pulse, was introduced to measure the ablation threshold and the on line ablation rate. This method was compared with other methods that use either a profilometer or the perforation of the sample to measure the ablation rate. It is shown that the acoustic method can provide accurate, o n line information of the ablation rate and threshold. It is also shown tha t the ablation rate is reduced considerably along the depth of the sample. (C) 2000 American Institute of Physics. [S0021-8979(00)00303-0].