Transmission of high Erbium:YAG laser pulse energies through germanium oxide trunk fibers with sapphire tips

Endoscopic applications of the Erbium:YAG laser have been limited due to the lack of a suitable optical fiber delivery system. This study compares the transmission of Er:YAG laser radiation through germanium oxide trunk fibers with silica or sapphire fiber tips for potential use in endoscopic tissue ablation. Er:YAG laser radiation with a wavelength of 2.94 mu m, pulse length of 300 mu s, pulse energies of 5-1360 mJ, and pulse rates of 3-10 Hz, was delivered through 1-m-long germanium oxide fibers with either 1-cm-long, 550-mu m-diameter silica or sapphire tips. Transmission through the germanium oxide/sapphire fibers measured 65 +/- 5% compared with 55 +/- 4% for the germanium oxide/silica fibers (P < 0.05). The damage threshold for the hybrid fibers averaged 309 +/- 44 mJ and 126 +/- 43 mJ, respectively (n = 7 fibers each) (P < 0.05). Maximum pulse energies transmitted through the fibers were 700 mJ and 220 mJ, respectively. Improved index-matching of the trunk fiber and fiber tip at 2.94 mu m resulted in higher transmission and damage thresholds for the germanium oxide/sapphire fibers. The germanium oxide/sapphire fiber may represent a promising mid-IR optical fiber delivery system for use in endoscopic applications of the Er:YAG laser requiring a flexible, biocompatible, and robust fiber delivery system for contact tissue ablation.