抄録
In irradiation of the medical laser through a optical fiber, a beam diverges with some conical angle, which results in irradiation and degeneration of the surrounding normal tissue is addition to the aimed area. Especially this happened frequently in endoscopical use of the laser because of the difficulty of maintaining the distance between fiber end and tissue.
In order to restrict the area of irradiation and gain high power density by focusing the laser beam, a optical fiber with lens tip was developed. A diameter of the optical fiber core was 0.6mm, lens diameter was 1.7mm and focusing distance was 2mm.
In early experiments there were many thermal damages at the fiber tip. In irradiation in water, bubbles emerged at the tip of the fiber which scatter laser beam and heat up to cause thermal damage of the lens and lowering of the irradiation power.
In order to solve these problems a nozzle was adapted to water jet or gas jet, which prevented adhesion of the bubble or heat damage of the lens and the laser power was maintained.
This lens tipped fiber was applied to destroy gall stones experimentally with successful results
