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

Abstract

Based on our measurements of the MVL thresholds, with and without GVD compensation, we conclude that the visible lesion thresholds produced by 44 fs pulses in rhesus eyes are increased in energy due to GVD. The MVL ED50 was reduced by one third when the pulse was pre-chirped to compensate for GVD in the eye. This reduction in amplitude also holds true in the artificial eye for the LIB ED50 bubble thresholds and the LDP ED50 plasma channels, when using pre-chirped pulses versus non-chirped pulses. We also conclude from the data presented that low-density plasmas, and not LIB cavitation bubbles, are the probable mediating factor at the visible lesion thresholds observed within live eyes, for pulse durations at and below 50 fs. Therefore, the plasma channel created by LDPs is the major damage mechanism, if not the only damage mechanism, at MVL threshold energies for these pulse durations.

Safety assessment in macaques of light exposures for functional two-photon ophthalmoscopy in humans

“…The shorter the pulse duration, the broader the spectral bandwidth, and thus the stronger the blur. In this study, second-order dispersion was precompensated for pulses delivered to the retina [61]. We are not yet able to measure the pulse duration at the retina.…”

“…However, based on ex vivo measurements on bovine eyes [60], the pulse duration can be expected to be shorter than 100 fs. In the sub-100 fs pulse regime, nonlinear optical effects such as self-focusing and plasma formation cannot be neglected [41,61]. In the ideal scenario of 55 fs, Gaussian-shaped pulses delivered to the retina with the maximum average power of 1 mW used in this study, the peak power is 214 W.…”

“…However, the ultrashort pulses could directly ionize the exposed medium and thus generate ~6·10 12 free electrons/cm 3 . Although this number is too low to cause laser induced breakdown (>10 20 electrons/cm 3 ) [61] or lowdensity plasma (>10 18 electrons/cm 3 ) [62,63], these free electrons could interact with tissue molecules and break chemical bonds in a photochemical manner.…”

Research of linear and nonlinear processes at femtosecond laser radiation propagation in the medium simulating the human eye vitreous

“…Нуж-но отметить, что процесс самофокусировки происходит лавинообразно, поэтому при более высоких мощностях происходит схлопывание пучка, не поддающееся численному моделированию. Данные рас-четных значений соответствуют данным более ранних экспериментальных исследований [7] и показыва-ют, что при превышении обозначенного порога вероятность необратимого повреждения сетчатки суще-ственно возрастает. …”

“…В настоящей работе рассмотрены процессы ли-нейного и нелинейного распространения фемтосекундного лазерного излучения в стекловидном теле человеческого глаза и, исходя из анализа предыдущих работ [5,6], предложена математическая модель, адекватно описывающая данные процессы. К тому же распространение рассмотрено для динамики элек-тромагнитного поля без использования приближения медленно меняющихся огибающих [7] и с учетом временного расплывания импульсов.…”