It is shown that the acoustic waves generated during laser ablation can be used to determine the ablation threshold and the ablation rate for different fluences and depths and also to characterize the different regions of the process. On-line measurement of the individual ablation rate is possible by observation of the delay of the arrival of the acoustic wave to a piezoelectric detector located behind the sample.

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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 and the ablation rate as a function of the energy flux were measured. The effect of the pulse repetition rate on the cartilage temperature and the influence of a flowing cooling gas were also investigated. A new method, based on 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 respect 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, on line information of the ablation rate and threshold. It is also shown that the ablation rate is reduced considerably along the depth of the sample.