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 investigate plasma induced surface ablation of soft tissue by infrared picosecond laser pulses with energies of about 1 mJ. The emission and propagation of shock waves in the irradiated tissue as well as in the surrounding air environment was studied. The pressure amplitudes of the shock transients 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 delays of 4-5 mu s referring to the laser pulse. Furthermore, generation and propagation of a surface deformation wave was observed. Thus, we present a detailed and consistent description of all phenomena occuring during plasma induced surface ablation of soft tissue.