Side-firing fiber for underwater tissue ablation with erbium laser radiation

For erbium laser radiation a side-firing fiber delivery device was constructed for arthroscopic operations. The device basically consisted of a ZrF 4 -fiber with a side-firing tip made of low OH-quartz. The feasibility of the underwater application and the dynamics of bubble formation at the submerged side-firing fiber tip were investigated by transmission experiments and time resolved flash lamp videography and compared to the bubble formation at the bare fiber tip. The drilling depth in water and the associated laser induced pressure waves were measured for both the side-firing and the bare fiber tip. The collapse pressure of the vapor bubbles generated at the side-firing tip turned out to be higher than those generated at the bare fiber tip. At a laser pulse energy of 200 mJ the collapse pressure at the side-firing tip and the bare fiber tip amounted to 47 bar and 14 bar, respectively. The maximum laser pulse energy reached at the distal fiber tip amounted to 200 mJ within a 400 microsecond(s) long pulse. These laser parameters are sufficient for medical applications like cutting biological tissue e.g. meniscus.