<title>Aspherically modified fiber tips have better focusing effect</title>

Spherically shaped laser probes, primarily used in laser angioplasty to unobstruct occluded arteries have weak focusing abilities in physiological media due to index mismatching. Three- D ray tracing was developed to calculate the light distributions of aspherically modified tips (parabolic, hyperbolic, etc.). It was found that the focusing effects of aspherical silica (n equals 1.457) tips are up to 3.0 times better than those of spherical tips. It is possible to increase the irradiance of tissue in water by about 6 to 9 times using normal silica fiber without total internal reflection. Experiments were performed in air and in water using normal silica fiber without total internal reflection. Experiments were performed in air and in water using registration of light distribution with a CCD-camera and confirmed the theoretical predictions. For aspherical sapphire (n equals 1.75) tips increasing of maximum irradiance is more than 16 times than for spherical probes. The spherically modified tips are more atraumatic due to rapid decrease in fluence rate distal from the position of highest irradiance. Three-D ray tracing is useful to optimize the design of different modified tips.