Abstract
High-repetition-rate burst-mode ultrafast-laser ablation and disruption of biological tissues depends on interaction of each pulse with the sample, but under those particular conditions which persist from previous pulses. This work characterizes and compares the dynamics of absorption and scattering of a 133-MHz repetition-rate, burst-mode ultrafast-pulse laser, in agar hydrogel targets and distilled water. The differences in energy partition are quantified, pulse-by-pulse, using a time-resolving integrating-sphere-based device. These measurements reveal that high-repetition-rate burst-mode ultrafast-laser ablation is a highly dynamical process affected by the persistence of ionization, dissipation of plasma plume, neutral material flow, tissue tensile strength, and the hydrodynamic oscillation of cavitation bubbles.
Highlights
Ultrashort-pulse lasers have proven themselves indispensable as tools of today’s industrial materials-processing, and have already come to dominate niche applications in ophthalmology and other clinical applications in medicine, including corneal dissection in IntraLASIK refractive-correction surgery, and femtosecond laser-assisted cataract surgery [1]
Dynamic measurements of absorption and scattering of 10-μs bursts of 1.5-ps laser pulses at 133 MHz repetition rate, in in hydrogel targets, have found absorption to rapidly increase at the beginning of each pulsetrain burst
In over 80% of the shots in this series, greatest absorption was found within the first 20 pulses. This strong initial absorption was followed by few-microsecond oscillations in the absorption fraction, with no correlation to intensity changes in the pulsetrain envelope; this oscillation and its timescale point to hydrodynamics driven in the hydrogel
Summary
Ultrashort-pulse lasers have proven themselves indispensable as tools of today’s industrial materials-processing, and have already come to dominate niche applications in ophthalmology and other clinical applications in medicine, including corneal dissection in IntraLASIK refractive-correction surgery, and femtosecond laser-assisted cataract surgery [1]. The several-hundred-nanometers thick layer of heated material created during the very brief irradiation rapidly decouples from the bulk material and is driven away by the high pressure-gradient across the thin heated layer, allowing the substrate material to remain relatively cool. It is this decoupling mechanism that halts thermal diffusion into the tissue, leading to the low collateral damage characteristic of ultrafast laser ablation as compared to ablation performed by longer-pulse counterparts [3,5,6]
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