<title>Time-resolved measurements of shock-wave emission and cavitation-bubble generation in intraocular laser surgery with ps- and ns-pulses and related tissue effects</title>

Abstract

Intraocular microsurgery relies on plasma generation with subsequent shock wave emission and cavitation bubble formation. To assess the potentials of photodisruption with picosecond pulses in comparison to the clinical techniques presently used, the shock wave characteristics and the bubble expension after optical breakdown with picosecond and nanosecond laser pulses were investigated by time resolved photography and acoustic measurements. Nd:YAG laser pulses with a wavelength of 1064 nm and a duration of 30 ps and 6 ns were focused into a water-filled glass cuvette. Their breakdown thresholds were 15 (mu) J and 200 (mu) J, respectively. Frequency doubled light from the same laser pulses was optically delayed between 2 ns and 136 ns and used as illumination source for photography. Since the individual events were well reproducible, the shock wave position and bubble wall position could be determined as a function of time. From the slope of these r(t) curves, the shock wave and bubble wall velocities were determined. The shock wave pressure p(r) was calculated from the shock velocity using the `jump conditions' of the shock front and the equation of state of water. The collateral effects of intraocular microsurgery can thus be considerably reduced by using ps-pulses, and with series of ps-pulses a `laser scalpel' may be realized which offers new applications of photodisruption.