The dynamics of shock waves and cavitation bubbles
generated by short laser pulses in water and elastic-plastic media were
investigated theoretically in order to get a better understanding of their
role in short-pulsed laser surgery. Numerical simulations were performed
using a spherical model of bubble dynamics which include the elastic-plastic
behaviour of the medium surrounding the bubble, compressibility, viscosity,
density and surface tension. Breakdown in water produces a monopolar
acoustic signal characterized by a compressive wave. Breakdown in an
elastic-plastic medium produces a bipolar acoustic signal, with a leading
positive compression wave and a trailing negative tensile wave. The
calculations revealed that consideration of the tissue elasticity is
essential to describe the bipolar shape of the shock wave emitted during
optical breakdown. The elastic-plastic response of the medium surrounding
the bubble leads to a significant decrease of the maximum size of the
cavitation bubble and pressure amplitude of the shock wave emitted during
bubble collapse, and shortening of the oscillation period of the bubble. The
results are discussed with respect to collateral damage in short-pulsed
laser surgery.