Ray-Tracing Calculations of the Focusing Efficiency of Spherical Fiber Ends

Optical fibers with spherically shaped tips have been proposed and used in surgery for different applications such as laser angiosurgery /1/, photodynamic therapy /2/ and laser lithotripsy /3/. In the latter case there are two reasons for not using plane fiber ends: a) A plane fiber end emits divergent radiation. Therefore the laser-induced breakdown takes place exactly at the fiber end, thereby damaging the fiber tip. By shifting the point of highest intensity from the fiber end, there is less probability of damage. b) If the breakdown threshold energy can be reduced by focusing, stone destruction can be achieved with less laser energy, which means less danger of thermal tissue damage.