Liquid-core light guides for near-infrared applications.

The strong absorption of tissue water is responsible for the low ablation threshold for biological tissues at the Er:YAG and Er:YSGG laser wavelengths. These lasers are therefore considered to be promising tools for medical treatments. As the existing transmission systems are still unsatisfactory, three types of liquid-filled light guides are investigated here as alternatives to conventional near-IR fibers. In addition to mechanical advantages, the minimum attenuation is below 3 dB/m, and losses at bending radii down to 20 mm are negligible. The maximum output energy densities of 14.2 J/cm(2) (free-running Er:YAG) or power densities of 7 MW/cm(2) (Q-switched Er:YAG) are sufficient for soft-tissue ablation. When the liquid was circulated, much higher energy densities, exceeding the hard-tissue ablation threshold, were achieved. These properties make liquid-core light guides promising delivery systems for many near-IR applications, including medical ones.