Laser pulse shape influence on optically induced dynamic processes

In this paper, the influence of laser pulse shape on laser drilling process and on optoacoustic effect is studied. Results for two laser applications: laser drilling in aluminium and laser drilling in hard dental tissue are presented. Observed changes in the interaction processes are compared to the optoacoustic OA.signals. Results confirm that laser pulse shape might have a significant influence on the interaction processes and can be used to increase machining efficiencies. With laser pulse shape, one can effectively induce desired dynamics of the melted material. However, if the process is cumulative in its nature like in the case of drilling in dentin, then the laser pulse shape is less important. Optoacoustic signals are found to depend on the laser pulse shape. However, usually used signal parameters for on line monitoring are not linearly correlated with the drilling efficiency. At least more complex signal analysis is needed. Presented method of signal analysis enables determination of the onset time of changes in the interaction mechanism and determination of energy threshold in the case of hard dental tissue drilling. q1998 Elsevier Science B.V.