Focusing femtosecond (fs) laser pulses into transparent media, such as corneal tissue, leads to optical breakdown, generation of a micro-plasma and, thus, a cutting effect inside the tissue-provided the intensity at the focus exceeds a threshold which depends on the pulse duration. For fs pulses, the corresponding threshold pulse energy is reduced by some orders of magnitude compared with ns or ps pulses. At a low pulse energy, thermal and mechanical damage to surrounding tissue is minimized, enabling a highly precise cutting effect inside the tissue while leaving anterior layers unaltered. In the following, investigations concerning aspects of the interaction of ultrashort laser pulses with aqueous media are presented: in particular, detection of pressure transients and bubble formation. For the first time-to our knowledge-the content of the resulting gas bubbles was analysed by gas chromatography, giving evidence of molecular hydrogen. Secondly, the potential of three-dimensional cutting effects within the corneal stroma for refractive surgery applications was evaluated in vitro on freshly enucleated porcine eyeglobes. Laser pulses with a duration of 200-300 fs and energies of 1.5-600 mu J were provided by a mode-locked Ti:sapphire laser with subsequent chirped pulse amplification.
