Cutting Transparent Tissue with Ultrafast Lasers

Photoionization of atoms by high intensity laser allows deposition of energy inside transparent tissues. Multiphoton interactions can photodissociate molecules and, at higher energies, produce visible plasma. Thermal plasma emission from the focal area of a Bessel beamrelaxation of plasma can lead to explosive vaporization in the focal spot, accompanied by shock wave emission and bubble formation, which enables tissue cutting.

Typically, transparent tissues are cut by sequential application of ultrashort (ps - fs) laser pulses, each of which produces a dielectric breakdown in a single focal spot. We explore approaches to enhancement of transparent tissue dissection with ultrafast lasers.

A technique called “optical scissors” is based on hydrodynamic interactions between simultaneous cavitation bubbles originating from multiple laser foci. Simultaneous expansion and collapse of the bubbles enhances the cutting efficiency by increasing the dynamic deformations in tissue between the bubbles.

Two cavitation bubbles in gelatin rupturing tissue between them. Water jets produced during collapse of two cavitation bubbles can rupture tissue in between.

Cavitation bubbles following dielectric breakdown in a highly elongated focal zone of a fs laser.In approach called “optical needle”, laser beam is focused in an axially-extended zone, producing dielectric breakdown with aspect ratio exceeding 100, making a millimeter-long cut of 10 micrometers in width with a single pulse. Adjusting the laser beam profile with an amplitude or phase mask allows for controlling the axial position and the length of the cut without the need for axial scanning.

We study various mechanisms of interaction of ultrafast lasers with transparent tissues in UV, visible and IR parts of the spectrum.