We have developed the fiber-optic probe method to monitor the ablation bubble which is generated at the fiber tip during Ho: YAG laser (λ=2.1μm) ablation. We performed comparative measurements by means of time-resolved photography and this probe method. The backscattered probe light, that was the probe method signal, which was simultaneously delivered together with Ho: YAG laser was measured at the incident end of the fiber. The ablation bubble volume at the end of laser output was about 10mm3 at 240J/cm2 in water by the time-resolved photography, but it didn't obey a liner relation to the backscatterd light intensity. The results from the water irradiation experiments explained that the probe method signal indicated the ablation bubble behavior because the observed signal was consisits of boundary reflection between bubble and water and debris scattering in the bubble. In the case of the agar experiments at 240J/cm2 in fluence, photographies and measured waveform corresponded to a ablation bubble behavior.. At 500J/cm2 in fluence, the cavitation which induced tissue dissection could be observed by photographies after ablation bubble collapse. The decay of meaured waveform was longer, which was influenced by the cavitation.We confirmed the possibility of monitoring tissue dissection from mesured waveform by the fiber-optic probe method.
