Nonlinear dynamics of femtosecond laser interaction with the central nervous system in zebrafish

We report on the photodamage mechanism underlying the highly nonlinear interaction of femtosecond pulses at 1030 nm with the central nervous system tissue in living zebrafish (Danio rerio). Our study identifies two different cavitation regimes. The damage is confined and well-controlled at low repetition rates due to plasma-based ablation and sudden local temperature rise. At high repetition rates, the damage becomes collateral due to plasma-mediated photochemistry and is not influenced by the thermal accumulation of consecutive laser pulses. Furthermore, we investigate and quantify the role of fluorescence labels with linear and nonlinear absorption pathways in optical breakdown. To verify our findings, we examined cell death and cellular responses to tissue damage, including the recruitment of fibroblasts and immune cells at different time points post-irradiation. These findings contribute to advancing the emerging nonlinear optical microscopy techniques and provide a strategy for inducing deep-tissue, precise, and localized injuries using near-infrared femtosecond laser pulses