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Ultrafast-Laser Manufacture of Radially Emitting Optical Fiber Diffusers for Medical Applications

Photodynamic Therapy (PDT) is a gentle method to treat cancer through irradiation by light. To guarantee a positive result from the treatment, a complete illumination of the treated malignant volume has to be reached. The technical challenge is to specifically decouple light from a wave guide, inserted into malignant regions. The aim of this study was to measure and simulate the radiation profile of radially emitting diffusers. An ultrafast laser system combined with a rotational axis was used to machine the distal end of optical fibers. Cylindrical and tapered shaped diffusers were produced. A low power diode laser (λ = 670 nm) was coupled into the fiber to determine the emission profile, which was measured via a camera setup. The measured emission profiles were simulated using a 2D-Matlab model and a 3D-LightTools model. The simulated and measured intensity profile along the cylindrical and the tapered fiber tip is characterized by an intensity maximum at the beginning, constant intensity in the middle, and exponentially decreasing intensity at the end. The studies indicate that fiber diffusers with tailored 3D radiation profile can be manufactured using ultrafast lasers. Further investigations have to be performed to adapt the simulations to the measured data.