A Ti:Sapphire laser operating at 800 mn and 1 kHz repetition rate, was used to investigate
the damage induced to fresh cadaveric porcine tissues. The laser was held constant
at a focal spot diameter of 100 mum for pulse widths varying from 120-femtoseconds
to 7-nanoseconds yielding a maximum fluence of 12.7 J/cm(2) irradiation. Polarization
optics were used to reduce the energy per pulse to well below tissue ablation threshold
fluences. Hollow silica waveguides with a silver inner coating and bore diameters
of 300, 500, 750 and 1000 pin were also used for the Ti:Sapphire laser with output
pulses <150 fs duration and energy up to 700 mujoules. A high resolution motorized
X-Y-Z stage translated the tissue through the beam at 1 mm/sec. A Luxar Novapulse
CO2 surgical laser was used as a standard for comparison. Tissues were processed for
light, scanning and transmission electron microscopy by standard protocols. Tissue
samples were examined for tissue removal rates, thermal damage to adjacent tissue,
and cellular disruption for equivalent fluence levels. The Ti:Sapphire laser demonstrated
an increase in removal rate along with a decrease in thermal damage as the pulse widths
approached the femtosecond regime for a constant fluence. With femtosecond pulses,
ablation still occurred below fluences of 2 j/cm(2.) However, for nanosecond pulses,
ablation no longer occurred, showing a decrease in ablation threshold as the pulse
width decreases. Because of the reduced thermal effects compared to nanosecond pulses,
ultrafast lasers may offer a solution to more precise tissue removal with less damage
to surrounding cells as compared to more conventional surgical laser systems.
