Abstract
We demonstrate a highly elongated (aspect ratio over 500:1) optical breakdown in water produced by a single pulse of a picosecond laser focused with a combination of an axicon and a lens. Locations of the proximal and distal ends of the breakdown region can be adjusted by modifying radial intensity distribution of the incident beam with an amplitude mask. Using Fresnel diffraction theory we derive a transmission profile of the amplitude mask to create a uniform axial intensity distribution in the breakdown zone. Experimentally observed dynamics of the bubbles obtained with the designed mask is in agreement with the theoretical model. A system producing an adjustable cylindrical breakdown can be applied to fast linear or planar dissection of transparent materials. It might be useful for ophthalmic surgical applications including cataract surgery and crystalline lens softening.
Highlights
Ultrafast lasers are becoming increasingly popular for precise dissection of transparent materials and biological tissues
Laser intensity distribution in the focal area has been visualized using 2-photon fluorescence of the fluorescein added to the cuvette, which produced signal proportional to the laser intensity squared (Fig. 2)
With increasing pulse energy the initial bubble length increases primarily towards the beam origin, while the position of the distal end remains practically the same, which suggests that axial intensity steadily increases with distance from the axicon and drops abruptly behind a certain point
Summary
Ultrafast lasers are becoming increasingly popular for precise dissection of transparent materials and biological tissues. To form a continuous cut with a series of pulses, the rupture zones produced by each pulse should overlap. While this sequential approach allows for cuts of arbitrary three dimensional shapes, extensive dissection is time-consuming. Tissue segmentation along multiple surfaces in cataract surgery requires tens of seconds [5] During this time movements of an eye, even when attached to a suction ring, result in discontinuities of the cutting planes, and require additional pulses, or increased energy to compensate for the skipped segments. Applications that involve deep planar cutting, such as cataract surgery or lens softening, could benefit from a regime that produces dielectric breakdown along a line of 1-2mm in length with a single pulse
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