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 th e preablation level. Minimum collimated transmission (40%) was observe d at 30 mus delay. Transmitted probe examination by both diode array a nd integrating sphere measurements indicate the observed attenuation i s due to scattering of the incident probe beam and not due to absorpti on. The significant scattering at nanosecond delay times suggests onse t of the ablation process during the ArF pulse. Scattering therefore m ay affect the deposition of the 193 nm radiation in the ablation targe t.