Pump/probe transmission measurements of corneal tissue during excimer laser ablation.

Transient changes in the transmission of a 355 nm probe pulse through corneal tissue during 193 nm ArF laser ablation have been examined. A significant decrease in collimated transmission of the probe beam was observed for time delays between 10 ns and 1 ms after the 193 nm laser pulse. At 10 ns delay the collimated probe transmission was 70% of the preablation level. Minimum collimated transmission (40%) was observed at 30 microseconds delay. Transmitted probe examination by both diode array and integrating sphere measurements indicate the observed attenuation is due to scattering of the incident probe beam and not due to absorption. The significant scattering at nanosecond delay times suggests onset of the ablation process during the ArF pulse. Scattering therefore may affect the deposition of the 193 nm radiation in the ablation target.