Abstract: Ray-tracing was used to calculate the beam profiles and spatial intensity distributions of modified fiber tips used in laser angioplasty. The position of the highest irradiance and the increase in power density relative to the power density at the tip of a bare fiber were calculated for probes made of silica or sapphire, in air and water. The computations were compared to paraxial theory and measurements on ball-shaped fibers and hemispherical probes. The calculated beam profiles and the irradiance distributions of the probes were in agreement with the measurements. The position of the highest irradiance and the power density increase depended on the ratio between the radius of the sphere R$-s$/ and the fiber R$-f$/ and on the refractive index. Intermal reflections limited the power density increase for smaller ratios R$-s$//R$-f$/. In water, the description of beam propagation from silica probes using paraxial optics theory was not in agreement with the ray-tracing results. Ray-tracing is useful to analyze the optical characteristics and to optimize the design of optically modified fiber tips when paraxial optics theory cannot be applied.!
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