2016 年 82 巻 843 号 p. 16-00196
Holmium: YAG laser is effectively used for transurethral ureterolithotripsy (TUL). A single bubble is formed at a fiber tip when a laser with high absorption rate irradiates into water through an optical fiber. The bubble shows characteristic behavior when it grows and collapses. In the present study, the behavior of a bubble induced by the fiber type laser is observed with a high speed video camera. In addition, the impulse force is measured with a hand-made sensor. As the results, the instantaneous appearance and the strength of impulse force at bubble collapse are shown for various laser irradiation conditions. A bubble inception appears just after the laser irradiation at the fiber tip. The bubble grows to a characteristic form and collapses with a microjet near the fiber tip. In the case of a bubble generated near a solid wall, the bubble growth is suppressed with the adjacent wall, so that the impulsive force becomes weaker. The impulsive force on wall surface reaches to the maximum value at a distance from the wall to the fiber tip, where the bubble does not collapse at fiber tip but on the wall. It is pointed out that there is an optimum laser irradiation condition on the wall impact for TUL.
