Time-resolved measurements of shock-wave emission and cavitation-bubble generation in Intraocular laser surgery with ps- And ns-pulses and related tissue effects

Alfred Vogel, Stefan Busch, Mary Asiyo-Vogel


Intraocular microsurgery relies on plasma generation with subsequent shock wave emission and cavitation bubble formation. To asses 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 μJ and 200 μJ, 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 initial shock pressures were 17 kbar after ps-pulses with an energy of 50 μJ, and 21 kbar after 1 mJ ns-pulses. The pressure amplitude decayed much faster after the ps-pulses. The maximum expansion velocity of the cavitation bubble was 350 m/s after a 50 μJ ps-pulse, but 1600 m/s after a 1 mJ nspulse. 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. For assessing the possibilities of corneal intrastromal refractive surgery, the cavitation bubble dynamics in corneal tissue were analyzed by flash photography and compared to the bubble dynamics in water. The maximal bubble diameter reached in corneal tissue is less than one third of that reached in water. The bubble is, however, much larger than the evaporated tissue volume.

Original languageEnglish
JournalProceedings of SPIE - The International Society for Optical Engineering
Pages (from-to)312-322
Number of pages11
Publication statusPublished - 24.06.1993
EventOphthalmic Technologies III 1993 - Los Angeles, United States
Duration: 17.01.199322.01.1993
Conference number: 154035

Research Areas and Centers

  • Academic Focus: Biomedical Engineering


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