Investigation of the formation mechanism and morphology of the features created in the interior of cornea by femtosecond laser pulses

Laser assisted corneal surgeries often rely on the nonlinear absorption effect of ultrafast lasers to induce features in the interior of the cornea without affecting the surface. In particular, corneal flap formation in femtosecond assisted LaserAssisted in situ Keratomileusis (LASIK) is based on the bubble creation. This study focuses on the interaction between the tissue and the femtosecond laser. Interior of cornea is treated with tightly focused femtosecond laser pulses. Due to the nature of the process, heating of the tissue within and around the focal volume is practically instantaneous. The affected region is subject to thermoelastic stress that arises with the steep temperature elevation. To predict the size of the region subject to the morphological changes due to the laser treatment, the temperature field is calculated. Cavitation bubble initiation and expansion process, which acts as precursor to the stress induced tissue trauma, is studied as well. Theoretical findings are compared against experimental results. High-speed camera is utilized to assess the laser treatment process, showing the temporal development of the cavitation bubbles. The results obtained in this study facilitate a better understanding of the effects of femtosecond laser assisted corneal surgeries and help in choosing optimal laser parameters.