Effects of Laser-Induced Breakdown, Self-Focusing, and Plasma Shielding onUltrashort Pulse Propagation in the Eye

摘要

As part of a research program to understand and model eye damage produced byexposure to sub-nanosecond laser pulses, an effort is currently being made to model and analyze ultrashort pulse propagation from the comea to the retina. Both analytical models and numerical simulations are being used to analyze the effects of self-focusing, laser-induced breakdown (LIB), and plasma-pulse interaction. The modeling effort is coupled with experimental measurements of LIB thresholds and plasma shielding for visible, picosecond (psec) and femtosecond (fsec) pulses in water, which serves as a reasonable simulant for the vitreous humor of the eye. Comparison of LIB thresholds to the critical power for self-focusing indicates that self-focusing has little effect on LIB threshold for long psec pulses. For short psec and fsec pulses, however, numerical simulations show that self-focusing is critical to LIB in water. These results indicate that self-focusing may play a role in fsec pulse ocular damage, by influencing whether LIB and plasma-pulse interaction occur at the retina, in the vitreous, or both. Both the location of the LIB event and the amount of plasma shielding can significantly effect the degree of damage.