Evanescent wave delivery into a precise tissue area using fiber-optic probes

We demonstrate a novel all-optical-fiber system for infrared (IR) laser radiation delivery into a precise tissue area. The operating principal of the laser delivery system is based on the use of a direct laser-to-taper coupling and an IR delivery fiber with angle-shaped tip. In our experiment, instead of a conventional lens-based laser-to-fiber coupling we use an uncoated glass hollow taper for a laser-to-fiber coupling. It is a funnel-shaped grazing-incidence-based hollow taper. The laser emission is launched directly, without any focusing elements, into the taper and next into the delivery fiber by a direct taper-to-fiber coupling. The IR fiber delivers the forward emission from a Er:YAG laser (λ=2.94 μm) to the tissue to be treated. Moreover, in order to realize a regime of evanescent wave delivery, we use a specially shaped fiber tip with an angled (porro-prism) profile. When the fiber tip is out of the tissue area, the laser emission is backreflected at the angled tip due to total-internal-reflection. However, when the fiber tip is placed on absorbing tissue, it becomes "transparent" for laser emission because of the frustrated-total-internal-reflectance and the energy then is coupled into the absorber. When sufficient energy is transferred, dermatology or other precise surgical processes can be controlled or stopped.