Mechanical and thermal parameters in pulsed laser cutting of tissue

Abstract

We investigate the physical processes in tissue cutting resulting from absorption of pulsed 10.6 μm radiation impact in the flux density range <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.3 \cdot 10^{4} - 6 \cdot 10^{6}</tex> W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . A purely thermodynamical explanation of the cutting process is tested experimentally. It is shown that for pulse durations longer than a fraction of a μs, the temperature and pressure values describing the irradiated zone follow from the equilibrium properties of water and the radiation flux density. In the considered flux density range, they do not exceed the critical values of water. We demonstrate experimentally that material is removed from the area of radiation impact by evaporation and by ejection in the liquid state. The relative importance of these processes with respect to material removal turns out to depend on the laser parameters and dramatically on the viscosity of the target in its liquid state.