Focal spot shaping for femtosecond laser pulse photodisruption through turbid media

Femtosecond laser induced optical breakdown allows for high-precision cutting of transparent materials with low energy deposit and little peripheral damage for applications in micromachining and minimally invasive medical surgery. Little peripheral damage is especially important for laser incisions in the posterior eye due to the vicinity to the retina. When applying laser pulses through the anterior eye, aberrations are introduced to the wave front, which cause a distortion of the focal volume and an increase in required pulse energy for tissue manipulation through photodisruption. To decrease the pulse energy, aberrations need to be corrected to restore a diffraction limited focus. In this work, the influence of an aberration correction using adaptive optics on the required pulse energy for an optical breakdown was investigated. The aberrations were introduced in an eye model using HEMA as eye tissue substitute and corrected in an optical setup including a deformable mirror and a Hartmann-Shack-Sensor. The laser pulses were focused by a plano-convex lens and the induced impact was compared for the aberrated and the corrected case. The pulse energy required to obtain an effect was reduced when correcting for aberrations. Therefore, adaptive optics can reduce the risk for potential peripheral damage during ophthalmic surgery.