Retinal damage and laser-induced breakdown produced by ultrashort-pulse lasers

Abstract

Based on our measurements for the MVL thresholds and LIB bubble generation thresholds in the monkey eye, we conclude that in the femtosecond pulsewidth regime for visible laser pulses, LIB and self-focusing are contributing factors in the lesion thresholds measured. Our results may also explain why it is so difficult to produce hemorrhagic lesions in either the rabbit or primate eye with visible 100-fs laser pulses even at 100 microJ of energy.

Sub-50-fs laser retinal damage thresholds in primate eyes with group velocity dispersion, self-focusing and low-density plasmas

“…Although the live eye and the artificial eye are not identical optical systems, either in focal properties or induced aberrations, they are close enough for comparison of our LIB, LDP, and MVL threshold data (Table 6) to provide a useful guide in determining the probable threshold-level retinal damage mechanism for pulses in this time regime. It is also interesting to compare these 44-fs thresholds to MVL thresholds measured for pulse durations of 90 fs and longer, where GVD effects were minimal and LIB was shown to be a contributing factor in retinal damage [1]. Finally, the calculated self-focusing critical power, 1.4€0.7 MW for 810-nm pulses in water, can be compared to the peak powers corresponding to threshold-level exposures, providing a guide to the probable contribution of nonlinear self-focusing to thresholdlevel ocular damage.…”

“…LIB was shown to be the probable threshold-level retinal damage mechanism for the 90-fs exposures, and a superthreshold damage mechanism for 600-fs exposures. GVD effects were, of course, minimal and LDPs had yet to be suggested as a possible damage mechanism [1]. The peak powers for the MVL threshold-level exposures at 44 fs indicate that self-focusing is probably a significant contributor to ocular focusing and ocular damage in this time regime.…”

“…Several researchers [1,4,13,21] have studied the potential ocular effects of self-focusing and LIB for pulse durations greater than 80 fs. For these longer pulses the effects of GVD are small.…”

Determination of scattering properties and damage thresholds in tissue using ultrafast laser ablation

“…The NA is chosen to reduce the effects of spherical aberration, which can decrease the Strehl ratio as ablation depth is increased, 21 and to avoid self-focusing, which can cause damage before the intended focus or create a tighter focus, and lead to an underestimation of the ablation fluence threshold. 22,23 We ablate a 40 × 40 μm 2 FoV by scanning 512 lines at 1/16 frames per second, causing ∼0.078 μm separation between lines and ∼1.28 μm separation between pulses on the same line, resulting in a ∼20 pulse overlap. An FoV is ablated rather than a single point to better sample the tissue and provide a more accurate representation of l s and F th .…”

A Comparative study of retinal effects from continuous wave and femtosecond mode‐locked lasers

“…Raising and lowering the energy per femtosecond pulse in the modelocked train of pulses would not be expected to change this basically thermal injury effect until the peak power per individual femtosecond pulse exceeded that required for laser induced breakdown. The level of energy required to reach laser induced breakdown in an eye from an 800 nm 100 femtosecond pulse is quite high, 0.56 mJ/100 femtosecond pulse [37]. If this energy was incorporated into a 0.25 second 76-MHz mode-locked pulse-train, the energy in the total pulse would be greater than 10 J or 1700 times the energy used to produce a retinal lesion in this study.…”