9 March 2016 Studying ultrafast laser parameters to deter self-focusing for deep tissue ablation
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Abstract
Ultrafast pulsed lasers are a promising tool for precise and noninvasive tissue surgery. The high peak intensity of the pulses allows nonlinear interaction with tissue, causing three-dimensional confined ablation without thermal damage. However, deep tissue ablation has been limited to a few scattering lengths due to laser beam extinction. As pulse energies are increased to overcome attenuation, unwanted side effects can occur such as self-focusing, where the highly intense pulse alters the refractive index of the material, causing a lensing effect and long filaments of damage or complete beam collapse before the focus. Here, we examine laser parameters to overcome self-focusing for deep tissue ablation. Through imaging ablation voids with third harmonic generation, we show that increasing the pulse width from 200-fs to 2-ps reduces self-focusing induced focal plane shifting and avoids multiple filamentation altogether, resulting in deeper ablation without extended axial damage. Additionally, we simulate beam propagation for pulses of different central wavelengths, and show that longer wavelengths can ablate deeper because of decreased scattering in tissue and a subsequent reduction in self-focusing.
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Chris Martin, Chris Martin, Adela Ben-Yakar, Adela Ben-Yakar, "Studying ultrafast laser parameters to deter self-focusing for deep tissue ablation", Proc. SPIE 9740, Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XVI, 97401I (9 March 2016); doi: 10.1117/12.2213665; https://doi.org/10.1117/12.2213665
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