Abstract
We developed the new output geometries of laser fiber for the purpose of getting both small spot size and also beam enlargement. Small spot size of laser beam means high power density, which is used for the coagulation of stop bleeding of GI tract accurately and also used for the destraction of tumors or stones under the endoscopic manipulation. Requirements of the beam enlargement are brought about by photoradiation therapy and fluorescence examination studies, in vivo. We have many methods for focussing of laser beam out-put from fiber; microlens attached to fiber tip, use of graded index rod lens and waveguide grating lens, and so on. The microlens method has some problems such as lens size,power loss and heating by scattering or reflection of the laser beam on the lens surface. Fiber used in this study is commercially avairable single quartz fiber. We designed and analyzed ball-shaped, hemispheric and trapezoid tip fiber. Straight and tapered tip fiber were made just only for the purpose of comparison. Ball-shaped, hemispheric and trapezoid one showed a high power density at the focal point than straight one, however the power density is decreased rapidly due to the beam divergence. In trapezoid one, there showed something like hot spot even without lens. Tapered one is limited in low power density because light is spread out from the wide area of tip into large angles. Ball-shaped one shows the highest power density at the focal point. This means laser light can be focused into very small spot. Advantages of those rounded tip fiber-optics are summarized as follow; it is simple design and low cost. It can be reformed many times and also be applicable to any endoscopes.
