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 &mgr;m, pulse length of 300 &mgr;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-&mgr;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 &mgr;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.
Recent advances in Thulium fiber laser technology have resulted in the availability of a compact, inexpensive, tunable, mid-infrared laser for potential use in laser surgery. The objective of this study was to tune the Thulium fiber laser wavelength and corresponding optical penetration depth to match the tissue thickness, and thus produce full-thickness, watertight tissue closure during microsurgical laser welding of urinary tissues. 1-cm-length incisions were made, ex vivo, in porcine ureters. Thulium fiber laser radiation with a wavelength of 1873 nm, power of 550-650 mW, and 750-μm-diameter spot was delivered to the tissue in continuous-wave mode through a 600-μm silica optical fiber. The fiber was scanned over the weld site once at a rate of 0.1 mm/s using a motion controller and linear stage controlled by a PC. Optical coherence tomography, histology, flow rates, and temperature measurements were used to optimize and evaluate laser welding success. Histologic analysis demonstrated full-thickness welding of the ureteral wall. Weld success rates ranged from 67% (8/12) at an incident laser power of 550 mW to 91% (10/11) at 650 mW. Peak flow rates greater than 200 ml/min were measured, however, mean flow rates were only about 50 ml/min. Average tissue temperatures increased with incident laser power from 59-89<sup>o</sup>C. The tunable Thulium fiber laser may be useful for surgical applications requiring variable control of thermal coagulation depth, such as microsurgical laser tissue welding.
The Erbium:YAG laser is currently being tested experimentally for endoscopic applications in urology, including more efficient laser lithotripsy and more precise incision of urethral strictures than the Holmium:YAG laser. While side-firing silica fibers are available for use with the Ho:YAG laser in urology, no such fibers exist for use with the Er:YAG laser. These applications may benefit from the availability of a side-firing, mid-infrared optical fiber capable of delivering the laser radiation at a 90-degree angle to the tissue. The objective of this study is to describe the simple construction and characterization of a side-firing germanium oxide fiber for potential use in endoscopic laser surgery. Side-firing fibers were constructed from 450-micron-core germanium oxide fibers of 1.45-m-length by polishing the distal tip at a 45-degree angle and placing a 1-cm-long protective quartz cap over the fiber tip. Er:YAG laser radiation with a wavelength of 2.94 microns, pulse duration of 300 microseconds, pulse repetition rate of 3 Hz, and pulse energies of from 5 to 550 mJ was coupled into the fibers. The fiber transmission rate and damage threshold measured 48 +/- 4 % and 149 +/- 37 mJ, respectively (n = 6 fibers). By comparison, fiber transmission through normal germanium oxide trunk fibers measured 66 +/- 3 %, with no observed damage (n = 5 fibers). Sufficient pulse energies were transmitted through the side-firing fibers for contact tissue ablation. Although these initial tests are promising, further studies will need to be conducted, focusing on assembly of more flexible, smaller diameter fibers, fiber bending transmission tests, long-term fiber reliability tests, and improvement of the fiber output spatial beam profile.