TIME-RESOLVED IMAGING OF THE SURFACE ABLATION OF SOFT-TISSUE WITH IR PICOSECOND LASER-PULSES

Time resolved video photographs have been taken in order to investigat e plasma induced surface ablation of soft tissue by infrared picosecon d laser pulses with energies of about 1 mJ. The emission and propagati on of shock waves in the irradiated tissue as well as in the surroundi ng air environment was studied. The pressure amplitudes of the shock t ransients were determined from the measured shock velocities. A decay of the pressure amplitude below 100 MPa was observed within a distance of about 200 mu m from the center of laser induced optical breakdown. The dynamics of the ablation crater and the ejection of the ablation fragments was studied on a larger timescale. The maximum expansion of the ablation crater was measured to be about 200 mu m at temporal dela ys of 4-5 mu s referring to the laser pulse. Furthermore, generation a nd propagation of a surface deformation wave was observed. Thus, we pr esent a detailed and consistent description of all phenomena occuring during plasma induced surface ablation of soft tissue.